the ecology, distribution, conservation, and …

The Pennsylvania State University

The Graduate School

Intercollege Graduate Degree Program in Ecology

THE ECOLOGY, DISTRIBUTION, CONSERVATION,

AND MANAGEMENT OF PENNSYLVANIA’S SURFACE-DWELLING

CRAYFISH FAUNA WITH AN EMPHASIS ON THE EASTERN PART OF

THE STATE

A Dissertation in

Ecology

by

David Andrew Lieb

© 2011 David Andrew Lieb

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Doctor of Philosophy

December 2011

ii

The dissertation of David Andrew Lieb was reviewed and approved* by the following:

Robert F. Carline

Retired Adjunct Professor of Wildlife and Fisheries Science

Dissertation Advisor

Co-Chair of Committee

Eric Post

Professor of Biology

Co-Chair of Committee

Hunter J. Carrick

Professor of Aquatic Biology

James L. Rosenberger

Professor of Statistics

Katriona Shea

Professor of Ecology

David Eissenstat

Professor of Woody Plant Physiology

Chair of the Intercollege Graduate Degree Program in Ecology

*Signatures are on file in the Graduate School.

iii

Abstract

Although crayfish have long been the object of scientific inquiry and where studied

appear to be functionally (ecologically) important, much remains to be learned about their

ecology, distribution, and conservation. Even the most basic information (presence/absence data)

is lacking for the majority of species. The absence of adequate crayfish data is a major problem,

because many species are thought to be imperiled across all or parts of their range and even

species that were once widely distributed are rapidly disappearing. Anthropogenic disturbances,

especially crayfish introductions, appear to be responsible for many of these losses. The

replacement of native crayfish by introduced (exotic) crayfish represents a significant threat to

aquatic communities because introduced crayfish often become extremely abundant and can

destroy aquatic macrophyte beds, suppress benthic invertebrate communities, reduce fish

abundance and biomass, and negatively affect amphibian populations.

At the turn of the 20th century, Arnold E. Ortmann published a monograph describing the

crayfish fauna of Pennsylvania. Since then, very few crayfish studies have been published from

the state. The need to re-examine Pennsylvania‘s crayfish fauna and the opportunity to revisit

previously sampled areas to assess changes in the state‘s crayfish fauna over the past century

motivated much of this work. The need for basic ecological and conservation information

regarding Pennsylvania‘s crayfish fauna, as well as specific strategies for managing the state‘s

native species, provided further motivation. To fulfill these needs, I conducted a series of

crayfish studies in Pennsylvania. The findings of these studies and others were then utilized to

address a broader ecological question: what determines surface-dwelling crayfish community

structure?

iv

I first found that a previously unstudied, widely distributed assemblage of crayfishes

(Cambarus bartonii bartonii and Orconectes obscurus) inhabiting Spruce Creek in central

Pennsylvania had strong top-down effects on other invertebrates and reduced total invertebrate

density by 70%. Crayfish were in turn readily consumed by brown trout (Salmo trutta),

especially large trout ( 275 mm total length). Next, I surveyed Valley Creek in southeastern

Pennsylvania for crayfishes and discovered a rare species of crayfish [Cambarus

(Puncticambarus) sp., an undescribed member of the Cambarus acuminatus complex] that had

not previously been reported from the state. The basic life history characteristics, reproductive

status, and habitat preferences of C. (P.) sp. are described herein. Additional surveys in

southeastern Pennsylvania and comparisons of these results to historical data indicated that

exotic crayfishes have invaded many parts of the region, much of which no longer supports

native crayfishes. In addition, populations of C. (P.) sp. were discovered from three more

streams and are now known from a total of four streams in Pennsylvania, all of which are

threatened by urbanization and exotic crayfishes. This information, in combination with other

historical and contemporary data from Pennsylvania and nearby states collected for this study

and other studies, indicate that C. (P.) sp. is critically imperiled in Pennsylvania and possibly

across its range and that the range of another native Pennsylvania crayfish, Orconectes limosus,

has declined (retreated eastward) by > 200 km in Pennsylvania and northern Maryland, likely as

a result of exotic crayfishes. Although C. b. bartonii was found with exotic crayfishes in a

number of water bodies in Pennsylvania, it was typically a minor component of the crayfish

community and may not be able to persist in those systems indefinitely. An examination of

potential determinants of surface-dwelling crayfish community structure suggests that a

combination of local, regional, and historical processes operating across a variety of temporal

v

and spatial scales shape these communities. More specifically, the interplay of competition with

environmental conditions appears to limit the number of species that can occur in local

communities, whereas regional, historical, and more recently human influences likely determine

potential component species.

In light of these findings, the role of barriers (e.g., dams), environmental protection,

educational programs, and regulations in preventing crayfish invasions and conserving native

crayfishes is discussed and management initiatives centered on those factors are presented. The

need for methods to eliminate exotics and monitor natives is highlighted. Although tailored to a

specific regional fauna, the ideas presented in this dissertation have broad applicability and

would likely benefit many of North America‘s crayfishes and the ecosystems in which they

reside.

vi

Table of Contents

List of Figures ................................................................................................................................ ix

List of Tables ................................................................................................................................. xi

Acknowledgments......................................................................................................................... xii

Chapter 1 Introduction ................................................................................................................... 1

References ................................................................................................................................... 5

Chapter 2 The Functional Importance of Crayfish in a Mid-Atlantic Trout Stream ................... 14

Abstract ..................................................................................................................................... 14

Introduction ............................................................................................................................... 14

Study Area ................................................................................................................................. 16

Study Animals ........................................................................................................................... 17

Materials and Methods .............................................................................................................. 17

Caging Study ......................................................................................................................... 17

Trout Gut Contents ................................................................................................................ 21

Data Analysis ......................................................................................................................... 21

Results and Discussion .............................................................................................................. 22

Acknowledgments ..................................................................................................................... 25

References ................................................................................................................................. 25

Chapter 3 The Discovery and Ecology of a Member of the Cambarus acuminatus Complex

(Decapoda: Cambaridae) in Valley Creek, Southeastern Pennsylvania ....................................... 36

Abstract ..................................................................................................................................... 36

Introduction ............................................................................................................................... 37


Study Area ............................................................................................................................. 40

Crayfish Collections .............................................................................................................. 40

Habitat Measurements ........................................................................................................... 43

Data Analysis ......................................................................................................................... 43


Taxonomy .............................................................................................................................. 46

Community Composition ...................................................................................................... 47

vii

Life History Characteristics ................................................................................................... 48

Habitat Associations .............................................................................................................. 56

Conservation Status and Future Directions ........................................................................... 62

Acknowledgements ................................................................................................................... 63

References ................................................................................................................................. 63

Chapter 4 Crayfish Fauna of Southeastern Pennsylvania: Distributions, Ecology, and Changes

over the Last Century .................................................................................................................... 80

Abstract ..................................................................................................................................... 80

Introduction ............................................................................................................................... 81


Contemporary Data ................................................................................................................ 83

Historical Data ....................................................................................................................... 87


Taxonomy of C. (P.) sp. in Pennsylvania .............................................................................. 88

Overview of Crayfish Collections ......................................................................................... 88

Contemporary Distributions and Range Changes ................................................................. 90

Crayfish Associations .......................................................................................................... 100

Community Composition .................................................................................................... 102

Concluding Remarks and Conservation Implications ......................................................... 103

Acknowledgements ................................................................................................................. 104

References ............................................................................................................................... 104

Chapter 5 Conservation and Management of Crayfishes: Lessons from Pennsylvania ............ 126

Abstract ................................................................................................................................... 126

Introduction ............................................................................................................................. 127

Materials and Methods ............................................................................................................ 128

Assessing Changes at Individual Sites and Across the Landscape ..................................... 128

Conservation Classifications ............................................................................................... 130

Conservation Classifications ................................................................................................... 131

Cambarus (P.) sp. ................................................................................................................ 131

Orconectes limosus .............................................................................................................. 134

Cambarus b. bartonii ........................................................................................................... 137

viii

Management Needs and Implications ..................................................................................... 138

Crayfish Ban ........................................................................................................................ 138

Education and Outreach ....................................................................................................... 141

Role of Dams, Temperature, and Nutrients ......................................................................... 142

Eliminating Exotics ............................................................................................................. 145

Reducing Environmental Degradation ................................................................................ 147

Additional Sampling ............................................................................................................ 149

Acknowledgments ................................................................................................................... 150

References ............................................................................................................................... 150

Chapter 6 Determinants of Crayfish Community Structure ...................................................... 175

Introduction ............................................................................................................................. 175

The Combined Influence of Local, Regional, and Historical Factors ..................................... 177

Local Influences .................................................................................................................. 178

Regional and Historical Influences ...................................................................................... 181

Concluding Remarks ........................................................................................................... 182

References ........................................................................................................................... 183

ix

List of Figures

Figure 2.1. Map of the experimental pool in the lower reaches of Spruce Creek showing the

approximate positions of the cages, debris shields, and uncaged control during the caging

experiment..........................................................................................................................33

Figure 2.2. Mean (±1SE) invertebrate densities on bricks collected from cages with crayfish

(enclosures, □), cages without crayfish (exclosures, ●), and an uncaged control (▲) prior

to adding crayfish to enclosures (pre-sampling) and 32 days after crayfish addition (post-

sampling)............................................................................................................................34

Figure 2.3. Percent of wild brown trout collected from the lower reaches of Spruce Creek that

had crayfish in their stomachs at the time of capture. ........................................................35

Figure 3.1. Map of the eastern United States from Pennsylvania to South Carolina with an

enlargement of the study area. ...........................................................................................75

Figure 3.2. Length-frequency distribution of C. (P.) sp. collected from Valley Creek in 2003. ...76

Figure 3.3. Relationship between the % of the sampling area where cobble was either the

dominant or co-dominant substrate type (% cobble) and C. (P.) sp. density (no./m2) in

main-channel areas of pools...............................................................................................77

Figure 3.4. Relationship between depth (upper left), current velocity (upper right), substrate

characteristics and C. (P.) sp. density (no./m2) in lateral (♦) and main-channel (O) areas

of pools...............................................................................................................................78

Figure 3.5. Relationship between current velocity and C. (P.) sp. density (no./m2) in lateral (♦)

and main-channel (O) areas of riffles. ...............................................................................79

Figure 4.1. Map of eastern Pennsylvania with an enlargement of the study area and nearby

regions in the southeastern part of the state. Contemporary (1968-2007) crayfish

collection sites are denoted by closed circles (●) and are numbered consecutively

according to the scheme provided in Table 4.1. ..............................................................122

Figure 4.2. Map of the study area and nearby regions in southeastern Pennsylvania. Occurrences

of C. (P.) sp., introduced Orconectes (O. obscurus, O. rusticus, O. virilis), and introduced

Procambarus (P. acutus, P. clarkii) are shown on the map. ...........................................123


of C. b. bartonii, O. limosus, introduced Orconectes (O. obscurus, O. rusticus, O. virilis),

and introduced Procambarus (P. acutus, P. clarkii) are shown on the map. ..................124


of O. obscurus, O. rusticus, O. virilis, P. acutus, and P. clarkii are included on the

map. ..................................................................................................................................125

x

Figure 5.1. Map of Pennsylvania with historical and contemporary crayfish collection sites. ...169

Figure 5.2. Map of eastern Pennsylvania with historical and contemporary O. limosus collection

sites. .................................................................................................................................170

Figure 5.3. Map of eastern Pennsylvania with historical and contemporary O. obscurus collection

sites. .................................................................................................................................171

Figure 5.4. Map of eastern Pennsylvania with O. rusticus collection sites. ................................172

Figure 5.5. Map of eastern Pennsylvania with O. virilis collection sites.....................................173

Figure 5.6. Map of eastern Pennsylvania with historical and contemporary C. b. bartonii

collection sites. .................................................................................................................174

xi

List of Tables

Table 1.1. List of Pennsylvania crayfish species. ..........................................................................13

Table 2.1. Comparison of invertebrate densities between treatments (enclosures vs exclosures)

and sampling periods (pre-sampling vs post-sampling) using a repeated-measures, three-

factor ANOVA with pair as a blocking factor. ..................................................................32

Table 3.1. Physical characteristics of electrofished areas in Valley Creek. ..................................72

Table 3.2. Comparison of mean C. (P.) sp. carapace length between main habitats (pool vs

riffle), sub-habitats (lateral vs main channel), seasons (spring vs fall) and sexes (male vs

female) using a repeated measures (season factor included), five factor, strip-plot (also

called a split-block) ANOVA with station (1,2,3,4) as a blocking factor. ........................73

Table 3.3. Comparison of C. (P.) sp. density between main habitats (pool vs riffle), sub-habitats

(lateral vs main channel), and seasons (spring vs fall) using a repeated measures (season

factor included), four factor, strip-plot (also called a split-block) ANOVA with station

(1,2,3,4) as a blocking factor. ............................................................................................74

Table 4.1. Contemporary (1968-2007) crayfish collections at individual sampling sites in

southeastern Pennsylvania. ..............................................................................................116

Table 4.2. Comparison of contemporary (1968-2007) crayfish collections from the northern part

of the study area (northern sites) to those from the southern part of the study area

(southern sites). ................................................................................................................121

Table 5.1. Historical and contemporary crayfish studies that aided in the development of the

conservation classifications (e.g., vulnerable, secure) and management strategies

provided herein. ...............................................................................................................166

Table 5.2. Historical and contemporary crayfish collections from resampled sites in the

Susquehanna (S) and Potomac (P) River drainages of Pennsylvania. .............................167

Table 5.3. Conservation classifications for several of eastern Pennsylvania's native

crayfishes. ........................................................................................................................168

xii

Acknowledgments

The completion of this dissertation would not have been possible without the help

and encouragement of many family members, co-workers, and colleagues. Throughout my graduate

studies, I never doubted my wife‘s sincere belief in me and in the value of my research, which was a

source of continual encouragement. Not many wives would have understood the value of my work or

stuck by me to see it to completion. She also endured many long days and nights holding down the

fort while I focused on my research efforts and she skillfully reviewed many of my reports and

papers and helped format my dissertation. My wonderful daughters were, and continue to be, a

constant source of inspiration, always asking about what I had discovered and when possible visiting

me at field sites and joining me on collection trips. I couldn‘t ask for two more perfect daughters. My

parents were always there for me – providing constant encouragement and support throughout this

project. They also gave up huge chunks of their own time to help me in the field during the caging

study portion of my research. All while working very demanding jobs themselves. Very few (if any)

parents would have made the many, many sacrifices that they made for me. I would also like to thank

my grandparents and great uncle and aunt who did not live to see me complete this degree but who

provided me with continual encouragement and support and always emphasized the value of

education. They lost everything several times due to wars and the great depression and always told

me ―they can take all your possessions David but they can‘t take what‘s in your head.‖ This thesis

required hard work, determination, and persistence, all of which I learned from my parents. For all

these contributions, I can‘t thank my family enough.

I also greatly appreciate the many contributions of my thesis advisor, Robert F.

Carline, who I always felt believed in my abilities and gave me the freedom to pursue my own

interests and develop as a researcher. He has been a great mentor for me throughout my graduate

studies and I have very much enjoyed working with him over the years. Raymond W. Bouchard,

xiii

although not officially a member of my graduate committee, provided excellent advice and assistance

throughout much of this project. I am greatly indebted to him. Eric Post very kindly agreed to serve

as co-chair after Bob Carline‘s retirement and provided some important initial thoughts that

eventually led to Chapter 6. James L. Rosenberger provided statistical advice, which was very much

appreciated. My other committee members, Katriona Shea and Hunter J. Carrick also deserve thanks

for their contributions to my graduate studies.

Co-workers at Penn State, especially Jeremy Harper, Nellie Bhattarai, Hannah M. Ingram, V.

Malissa Mengel, Paula Mooney, Adam Smith, Kristin Babcock, Jonathan Freedman, Patrick

Kocovsky, Patrick Barry, Christa Walker and her husband, Brianna Hutchison, and Dan Counahan

provided extremely valuable assistance during this project and were a great group of people to work

with. Many of them worked extremely hard in the field and the lab during this project. Kay Christine

was always there to help in many ways – I can‘t thank her enough for all she has done for me over

the years. The support of the Pennsylvania Cooperative Fish and Wildlife Research Unit, especially

Duane Diefenbach, was of critical importance and is very much appreciated. Financial support was

provided by several institutions, and a number of colleagues assisted with various aspects of this

project, all of which are detailed in the acknowledgments sections of the reports and peer-reviewed

papers resulting from this work. Many thanks to all of you.

1

Chapter 1

Introduction

Crayfish occur naturally on every continent except Africa and Antarctica; however, their

diversity peaks in North America, where 400+ species and subspecies reside (Taylor 2002,

Taylor et al. 2007). Over two-thirds of these species and subspecies occur in the southeastern

United States, many of which are endemic to the region and appear to have arisen due to the

isolating effects of pre- and post-Pleistocene shifts in river drainages (Crandall and Templeton

1999, Taylor et al. 2007, Crandall and Buhay 2008).

Although crayfish have long been the object of scientific inquiry (see Huxley 1879),

much remains to be learned about the group. In North America, surprisingly little is known about

the ecology of most species. Although existing studies indicate that crayfish often account for a

major portion of macroinvertebrate biomass and production (Huryn and Wallace 1987, Momot

1995, Rabeni et al. 1995, Whitledge and Rabeni 1997, Dorn and Mittelbach 1999) and can affect

energy flow along multiple pathways, interact strongly with other invertebrates and primary

producers, and constitute an important food item for vertebrates including fishes, mammals,

birds, reptiles, and amphibians (see Rabeni 1992, Hobbs 1993, Roell and Orth 1993, Nyström

2002, Wilson et al. 2004, Geiger et al. 2005, McCarthy et al. 2006, Nyström et al. 2006, Gherardi

and Acquistapace 2007, Britton et al. 2010, Tetzlaff et al. 2011, and references within), too few

data are available to assume their importance in all systems, especially given the inherent

biological differences among crayfish species and the wide range of habitats (e.g., caves,

swamps, lakes, streams, rivers, estuaries) that they occupy (Nyström 2002). To date,

commercially-important, widely-introduced species such as the red swamp crayfish

2

(Procambarus clarkii), rusty crayfish (Orconectes rusticus), and signal crayfish (Pacifastacus

leniusculus) have been the focus of most research efforts, whereas other North American species

have been neglected.

Even the most basic ecological information (presence/absence data) is lacking for the

majority of North American crayfish species. For example, Taylor et al. (2007) estimated that

current distributional information is available for only 40% of the United States and Canadian

fauna. Even where adequate contemporary data are available, the absence or scarcity of historical

collections, particularly for large geographical areas (entire states), often makes it difficult to

assess long-term changes across landscapes. Without such data it is hard to accurately classify

individual species (endangered, threatened, stable) and develop conservation strategies for those

in decline (Jones et al. 2005, Taylor et al. 2007).

The absence of adequate crayfish data is a major problem, because many North American

species have limited distributions, are threatened by exotic (introduced) crayfish, habitat

destruction, pollution, urbanization, and other human influences, and are thought to be imperiled

across all or parts of their range (Master 1990, Taylor et al. 1996, Hamr 1998, Master et al. 1998,

Master et al. 2000, Wilcove et al. 2000, Lodge et al. 2000, Taylor 2002, Taylor et al. 2007). Even

species that were once widely distributed are rapidly disappearing due to anthropogenic

disturbances, especially crayfish introductions (Hamr 1998, Bouchard et al. 2007, Loughman et

al. 2009, Kilian et al. 2010, Swecker et al. 2010, Lieb et al. 2011a, b), which typically result from

intentional stocking efforts, dispersal via man-made canals, and the release or escape of fishing

bait, aquarium and pond pets, and classroom, laboratory and aquaculture species (see Lodge et

al. 2000, Taylor et al. 2007).

3

The replacement of native crayfish by introduced crayfish is believed to occur as a result

of competition for shelter and food, differential susceptibility to fish predators, and/or

reproductive interference and hybridization (Didonato and Lodge 1993, Hill et al. 1993, Garvey

et al. 1994, Hill and Lodge 1994, Lodge et al. 2000, Perry et al. 2001). In some systems,

replacements appear to occur rapidly (likely in <10 years) and interactions between exotic and

resident crayfishes can result in injuries to residents (D.A. Lieb, PSU, personal observations).

Based on existing information, it appears that successful crayfish invasions do not require

vacant niches (Hill et al. 1993). It also appears that, at the scale of individual streams, introduced

crayfish do not always have wider niches than their native counterparts, although at larger,

regional scales some invaders do have wider niches, allowing them to occupy a greater variety of

stream types (Olsson et al. 2009).

The replacement of native crayfish by exotic crayfish represents a significant threat to

aquatic communities because densities of introduced crayfish can approach 200 individuals/m2

(Roth and Kitchell 2005) and are often an order of magnitude higher than their native

counterparts. At such high densities, introduced crayfish frequently destroy aquatic macrophyte

beds and suppress benthic invertebrate communities (Lodge et al. 1994, Nyström 2002,

McCarthy et al. 2006). In addition, introduced crayfish tend to be less vulnerable to fish

predation than native crayfish because many introduced crayfish quickly grow to a size that

reduces their susceptibility to predation, possess large chelae, and are aggressive (Didonato and

Lodge 1993, Mather and Stein 1993, Garvey et al. 1994, Roth and Kitchell 2005). Introduced

crayfish also readily consume fish eggs and can have strong negative effects on fish reproduction

(Dorn and Mittelbach 2004, Dorn and Wojdak 2004). The end result for affected fish populations

4

is often less food, decreased recruitment (Covich et al. 1999), and ultimately reduced abundance

and biomass (Wilson et al. 2004, Roth et al. 2007, Bobeldyk and Lamberti 2010).

Introduced crayfish have also been implicated in global amphibian declines (Kats and

Ferrer 2003) and have strong negative effects on a variety of amphibian species. For example,

introduced crayfish have been shown to readily consume the eggs and larva of California newts

and have been implicated in their disappearance from streams in the Santa Monica Mountains

(Gamradt and Kats 1996). Introduced crayfish have also been associated with ranid frog

disappearances in Arizona (Witte et al. 2008), declines in Pacific tree frog abundance in

California (Riley et al. 2005), and decreased salamander breeding success and amphibian species

richness in southwestern Portugal (Cruz et al. 2006).

In Pennsylvania, although contemporary data are scarce and mostly unpublished,

historical collections dating back more than 100 years are available for large areas of the state

(Ortmann, 1906). Ortmann‘s monograph is one of the most thorough and important crayfish

studies ever conducted and one of the few large-scale surveys of its vintage from North America.

Nonetheless, given that over 100 years have passed since Ortmann‘s study, a reexamination of

Pennsylvania‘s crayfish fauna is overdue. It is important to note that the availability of historical

data from Ortmann (1906) provided me the unique opportunity to revisit previously sampled

areas to assess changes in Pennsylvania‘s crayfish fauna over the past century.

From this discussion, it is clear that much remains to be learned about the ecology,

distribution, and conservation of North America‘s crayfish fauna. The main objective of this

study is to address this need for some of eastern Pennsylvania‘s surface-dwelling crayfishes and

in the process provide up-to-date information regarding the state‘s fauna. A list of the surface-

dwelling crayfish species that currently occur in eastern Pennsylvania, their status in the state

5

(native, exotic), and the location of voucher material deposited in museums during this study is

provided in Table 1.1.

To meet the objective of this study, I first assessed the functional (ecological) importance

of a previously unstudied, widely distributed assemblage of crayfishes (Cambarus bartonii

bartonii and Orconectes obscurus) inhabiting a mid-sized stream in central Pennsylvania by

using caging studies and dietary information to determine if these crayfishes affect the density of

other invertebrates and are an important food item for brown trout (Salmo trutta). I then

determined the basic life history characteristics, reproductive status, and habitat preferences of a

rare species of crayfish inhabiting Valley Creek in southeastern Pennsylvania. Next, I determined

the distribution and ecology of southeastern Pennsylvania‘s crayfish fauna and compared those

findings to those of Ortmann (1906) to estimate change over the last century. I then utilized a

combination of historical and contemporary data from Pennsylvania and nearby states collected

for this study and others to determine the conservation status of several native crayfishes and

develop management strategies for those species. Finally, I utilized the findings of this study and

others to address a broader ecological question: what determines surface-dwelling crayfish

community structure?

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Bouchard, R.W., D.A. Lieb, R.F. Carline, T.R. Nuttall, C.B. Wengert, and J.R. Wallace. 2007.

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8

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12

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13

Table 1.1. List of surface-dwelling crayfish species that are currently found in the eastern half

of Pennsylvania. The status of each species is either native to all or part of Pennsylvania (N) or

not native (exotic) to the state (E). Representative voucher specimens collected by the author

and colleagues were deposited in museums (Repositories). Cambarus robustus and Orconectes

propinquus specimens were vouchered as a part of another study (Bouchard et al. 2007); a

Procambarus acutus specimen from southeastern Pennsylvania is in the United States

National Museum, Smithsonian Institution crayfish collection. NCSM=North Carolina State

Museum of Natural Sciences, ANSP=Academy of Natural Sciences of Philadelphia,

OSU=Ohio State University Museum, CM=Carnegie Museum of Natural History. See the

Materials and Methods sections of Chapters 3 and 4 for catalog numbers.

Species Status Repositories

Cambarus (Puncticambarus) sp.1

N NCSM, OSU, CM, ANSP

Cambarus bartonii bartonii N ANSP

Cambarus robustus N -

Orconectes limosus N ANSP

Orconectes obscurus N ANSP

Orconectes propinquus N -

Orconectes rusticus E ANSP

Orconectes virilis E ANSP

Procambarus acutus N -

Procambarus clarkii E ANSP

1An undescribed member of the Cambarus acuminatus species

complex

14

Chapter 2

The Functional Importance of Crayfish in a Mid-Atlantic Trout Stream

Abstract

Although crayfish are often assumed to be functionally (ecologically) important, only a

handful of North America‘s 400+ species and subspecies have been well studied. To address this

deficiency, I used caging studies and dietary information to assess the functional importance of a

previously unstudied assemblage of crayfishes (C. b. bartonii and O. obscurus) inhabiting a mid-

sized stream (Spruce Creek) in eastern North America. I found that crayfishes had strong top-

down effects on other invertebrates and reduced total invertebrate density by 70%. Crayfish were

in turn readily consumed by brown trout (Salmo trutta), especially large trout ( 275 mm total

length). These results indicate that crayfish are functionally important in Spruce Creek,

facilitating the transfer of nutrients up the food chain to a recreationally-valuable fish species,

and add to the growing body of information that suggests that crayfish are functionally important

wherever they occur and are deserving of policy directed at their preservation.

Introduction

Although North America is home to a diverse crayfish fauna (400+ species and

subspecies) that is highly threatened by human activities (Master et al. 1998, Wilcove et al. 1998,

15

Lodge et al. 2000, Taylor et al. 2007), our understanding of their functional (ecological) role in

aquatic systems is limited to a handful of species, most of which are native to the Midwest and

West (e.g., O. rusticus, P. clarkii, and P. leniusculus). Few of eastern North America‘s

crayfishes have been studied.

Where examined, crayfish often account for a major portion of macroinvertebrate

biomass and production (sometimes > 50%) (Huryn and Wallace 1987, Momot 1995, Rabeni et

al. 1995, Whitledge and Rabeni 1997, Dorn and Mittelbach 1999), exert direct and indirect

effects on basal resources (detritus, algae, macrophytes) and other invertebrates (see Nyström

2002, Wilson et al. 2004, Geiger et al. 2005, McCarthy et al. 2006, Gherardi and Acquistapace

2007, and references within), and are an important food item for fishes, including recreationally

and commercially important species (Rabeni 1992, Roell and Orth 1993, Nyström et al. 2006,

Britton et al. 2010, Tetzlaff et al. 2011). Crayfish are also readily consumed by a variety of other

vertebrates including mammals, birds, reptiles, and amphibians (Hobbs 1993). Based on these

studies, it is tempting to conclude that crayfishes are functionally important wherever they occur,

affecting energy flow along multiple pathways and facilitating the transfer of nutrients up

through the food chain to fishes and other vertebrates; however, too few data are available for

such generalizations, especially given the inherent biological differences among crayfish species

and the wide range of habitats (e.g., caves, swamps, lakes, streams, rivers, estuaries) that they

occupy (Nyström 2002).

The objective of this study was to assess the functional importance of a previously

unstudied assemblage of crayfishes (C. b. bartonii and O. obscurus) inhabiting a mid-sized

stream in eastern North America by determining if these crayfishes affect the density of other

invertebrates and are an important food item for brown trout (Salmo trutta).

16

Study Area

This study was conducted in Spruce Creek, which is located in the Valley and Ridge

Physiographic Province of the Appalachian Mountains in central Pennsylvania and is in the

Susquehanna River drainage. The climate of the region is temperate and yearly precipitation

averages approximately 98 cm. Spruce Creek originates from limestone springs and flows for

approximately 26 km through mostly forest and agricultural land before emptying into the Little

Juniata River (Carline 2001).

Spruce Creek is a mid-sized (~5-12 m wide), alkaline stream (~150 mg CaCO3/L) with

temperatures that generally range from 3-20 °C, nitrate and ortho-phosphorous concentrations

that average 3.2 and 0.02 mg/L, respectively, and conductivities near 280 uS/cm [Bachman 1984,

Carline 2001, and R.F. Carline, United States Geological Survey (USGS), The Pennsylvania

State University (PSU), unpublished data]. Discharge averages about 1.7-2.8 m3/s (Bachman

1984, R.F. Carline, USGS, PSU, unpublished data) and the stream bottom is primarily cobble

intermixed with gravel.

Study sites were within Penn State University‘s George W. Harvey Experimental

Fisheries Research Area (PSU Research Area), which is located in the lower reaches of Spruce

Creek, approximately 1 km upstream of the Little Juniata River. Total crayfish densities in pools

in lower Spruce Creek range from 22±1 individuals/m2 (mean±1SE, n=4) in rocky areas to 39±7

individuals/m2 (mean±1SE, n=6) in lateral, silty areas with shoreline root masses and/or

vegetation (D.A. Lieb, PSU, unpublished data). Densities of juvenile crayfish range from 10±2

individuals/m2 in rocky areas to 26±5 individuals/m

2 in lateral areas. Densities of adult crayfish

range from 12±3 individuals/m2 in rocky areas to 13±4 individuals/m

2 in lateral areas (D.A.

17

Lieb, PSU, unpublished data). Two crayfish species (C. b. bartonii and O. obscurus) occur in

lower Spruce Creek; O. obscurus is the dominant species in pools (relative abundance=76-99%,

n=619) (D.A. Lieb, PSU, unpublished data), whereas C. b. bartonii is the dominant species in

riffles (D.A. Lieb, PSU, personal observations). Wild brown trout (Salmo trutta) are common in

lower Spruce Creek (Carline 2001).

Study Animals

Orconectes obscurus is native to western Pennsylvania (Ohio River, Genesee River, and

Lake Erie drainages) and nearby states (Ortmann 1906, Hobbs 1989) but has been widely

introduced in Pennsylvania and now occurs throughout the state (Bouchard et al. 2007, Lieb et

al. 2011a, b). The native range of C. b. bartonii extends from Canada southward to Georgia and

includes the Delaware, Potomac and Susquehanna River drainages in eastern Pennsylvania

(Hobbs 1989, Thoma and Jezerinac 1999). Orconectes obscurus and C. b. bartonii often co-

occur in Pennsylvania (Lieb et al. 2011a) and elsewhere (Jezerinac et al. 1995, Hamr 1998,

Kuhlmann and Hazelton 2007) and are frequently found in streams with brown trout (D.A. Lieb,

PSU, personal observations). Cambarus b. bartonii is native to Spruce Creek, whereas O.

obscurus was probably introduced to the stream.

Materials and Methods

Caging Study

Basic Design and Experimental Setup. — A 34-day caging experiment with two

treatments [cages with crayfish (enclosures), cages without crayfish (exclosures)], each

18

replicated five times, and one uncaged control (Figure 2.1) was conducted to determine whether

crayfish affect benthic invertebrate density in Spruce Creek. The experiment was carried out

from 17 September-20 October 2002 in a large pool (~80 m long × 12 m wide, hereafter referred

to as the experimental pool) at the upstream end of the PSU Research Area. I used a randomized

complete block design, because there was considerable within pool variability in the benthic

invertebrate assemblage. Within each of the five blocks (pairs), cages were placed side by side

(<1 m apart) in similar habitats. Differences in flow, depth, and light levels between treatments

were <0.01 m/s, <0.05 m, and <56 µmole quanta m-2

s-1

, respectively for all pairs. Debris shields

constructed of 6-mm wire mesh were placed 2-3 m upstream of each pair to provide protection

and reduce debris accumulation. Pairs of cages were spaced fairly evenly across the pool in a

longitudinal (upstream-downstream) direction with 16-28 m between pairs.

The cages consisted of square wooden frames (0.84 m2) equipped with metal screens (6-

mm mesh) on the bottom and each of the sides. The tops of the cages were open. Six-millimeter

mesh was selected because it retains/excludes all but the smallest crayfish while allowing most

other invertebrates to move in and out of the cages freely (Hart 1992). A mixture of bricks (12

per cage) and landscaping gravel (0.04 m3 per cage) was added to the cages to mimic the

dominant substrates (cobble and gravel) in Spruce Creek. Bricks were conditioned for about one

week in Spruce Creek before being placed in cages; bricks and gravel were evenly distributed

across the bottoms of the cages. Cages were assembled and placed in the experimental pool on 9

September 2002, eight days prior to the start of the experiment (hereafter referred to as the pre-

conditioning period). Cages were scrubbed 3-4 times per week throughout the experiment to

prevent clogging.

19

An uncaged area (0.84 m2) was set up near the cages and served as an uncaged control.

Landscaping gravel and bricks were added to the uncaged control and arranged as in the cages.

The uncaged control lacked an upstream debris shield. Depth, velocity, and light levels in the

uncaged control were similar to those in the cages. Free-ranging crayfish were frequently

observed in the uncaged control.

Ideally, I would have included the following in my experiment: (1) additional uncaged

controls, (2) an additional treatment (side-open control) with multiple replicates, (3) multiple

pools, and (4) multiple years. Having additional uncaged controls would have allowed my

control treatment to be included in statistical analyses; side-open controls would have allowed

caging effects to be fully assessed (by comparing uncaged controls to side-open controls); and

the inclusion of multiple pools and years would have allowed an assessment of spatial and

temporal variability. Later experiments (conducted in 2004 and 2005) included all those

elements; unfortunately, the resources necessary to process all the samples from those

experiments and analyze those data were not available.

Addition of Crayfish to Cages. — One cage in each pair was randomly selected and

stocked with crayfish (C. b. bartonii and O. obscurus) at densities (12 juveniles and 8 adults/m2)

that were near the low end of the range found naturally in the study area. Crayfish community

composition in the cages (70-100% O. obscurus, the rest C. b. bartonii) matched that in pool

areas of lower Spruce Creek. The crayfish stocked in the cages were collected from the lower

reaches of Spruce Creek. Carapace length (distance from tip of rostrum to the posterior median

margin of the carapace; CL) for the juvenile and adult crayfish stocked in the cages averaged

18±0.2 mm (mean±1SE) and 35±0.4 mm, respectively. The uropods (tails) of all stocked crayfish

20

received a small clip prior to adding them to the cages. During the experiment, some crayfish

escaped the enclosures (crayfish cages) resulting in average final densities (10 juvenile and 3

adult crayfish/m2) that were much lower than natural. More specifically, the average total

crayfish density in the enclosures at the end of the experiment was 41% lower than that naturally

found in rocky areas and 67% lower than that naturally found in lateral, silty areas of pools in

lower Spruce Creek. All of the crayfish recovered from the enclosures at the end of the

experiment had uropod clips indicating that, although the enclosures did not prevent some

stocked crayfish from escaping, they did effectively exclude free-ranging crayfish. The

exclosures (crayfish-free cages) were also generally effective in preventing unwanted crayfish

entry resulting in low exclosure densities (0-2 individuals/m2) at the end of the experiment. The

few crayfish that were found in the exclosures were unclipped and very small (10-13 mm CL).

The presence of a few small crayfish in exclosures and much lower than natural densities in

enclosures did not compromise the results of this experiment, instead, this experiment represents

a robust test of the effect of crayfish on benthic invertebrates in Spruce Creek.

Sample Collection and Processing. — Invertebrate samples were collected from

treatment and uncaged control bricks 1 day prior to adding crayfish to cages (both treatments

crayfish-free; pre-sampling) and 32 days after crayfish addition (one treatment with crayfish, the

other crayfish-free; post-sampling). Samples were collected by gently lifting bricks and

associated materials (e.g., detritus, inorganic particles) into a 500- m dip net positioned

downstream of the sampling locations. Bricks were then scrubbed with a brush and hand-picked

with forceps to remove attached invertebrates. After collection, samples were preserved in 10%

buffered formalin. Invertebrates were later separated from associated materials under

21

magnification (dissecting microscope, 4-50 X power), identified (most insects to genus/species

and most non-insects to class/order), and counted.

Trout Gut Contents

To determine whether brown trout in Spruce Creek consume crayfish, a total of 209

brown trout from the PSU Research Area, ranging from 165 to 406 mm total length (TL), were

examined for the presence of crayfish in their stomachs. Trout were collected on June 14, 1996

using electrofishing gear and immediately transported to the stream bank where they were x-

rayed using a portable x-ray machine (see Weber and Carline 2000 for further methodological

details). Because crayfish were clearly visible in the stomachs of x-rayed trout (due to their

hardened, calcified exoskeletons), visual inspection of x-rays was used to assess the presence of

crayfish. Although these data were collected six years prior to the caging study, we assume that

they provide an approximate estimate of crayfish consumption rates in Spruce Creek at the time

of the caging study. Because newly molted crayfish have soft exoskeletons and are probably not

discernible in x-rays, the x-ray data provided herein may underestimate the number of crayfish

consumed. Data are presented separately for small (< 275 mm TL) and large ( 275 mm TL)

trout because there appeared to be a natural break in the data, whereby more large than small

trout had crayfish in their stomachs.

Data Analysis

A repeated-measures, three-factor (pair, treatment, sampling period) ANOVA with pair

as a blocking factor was used to compare total invertebrate densities on bricks between

22

treatments (enclosures vs. exclosures) and sampling periods (pre-sampling vs. post-sampling).

All 2-way interaction terms were included in the model. The treatment×sampling period

interaction was of particular interest because significance indicates that the treatment effect

differed between sampling periods (e.g., enclosures and exclosures differed during post-sampling

but not during pre-sampling). Analyses were completed as described in Green (1993).

Invertebrate densities were fourth-root transformed prior to analysis to correct for non-normality

and unequal variances. Fourth-root transformations are often employed in benthic studies (Burd

et al. 1990) and appear to be more effective than other more common transformations (e.g., log,

square root) in some situations (Downing 1979, Downing 1980, Taylor 1980a, Taylor 1980b,

Downing 1981). Additional details regarding these analyses can be found at

http://www.stat.psu.edu/~jlr/pub/Lieb/.

A Chi-square test was used to compare the proportion of large trout with crayfish in their

stomachs to the proportion of small trout with crayfish in their stomachs. For all analyses, p-

values <0.05 were considered significant and Minitab Release 15 (Minitab, Inc., State College,

Pennsylvania) was employed.

Results and Discussion

Prior to adding crayfish to cages, invertebrate densities in the treatments were almost

identical; whereas, 32 days after crayfish addition, the difference between the treatments was

striking (Figure 2.2; significant Treatment × Sampling Period interaction, Table 2.1). Cages with

crayfish had 70% fewer invertebrates than cages without crayfish, clearly demonstrating that

crayfish have strong top-down effects on other invertebrates in Spruce Creek. Invertebrate

densities in enclosures resembled those in the uncaged control, suggesting that crayfish effects

23

were similar regardless of whether the crayfish were caged or free-ranging. Invertebrate densities

increased in the treatments and the uncaged control during the experiment (based on the visual

inspection of Figure 2.2), suggesting that the bricks were not completely colonized by

invertebrates at the time of pre-sampling.

Although invertebrate densities in the uncaged control tracked those in the enclosures

during the experiment, control densities were somewhat lower than enclosure densities (based on

the visual inspection of Figure 2.2). This could have been due to the fact that during the pre-

conditioning period, the uncaged control was accessible to free-ranging crayfish; whereas the

enclosures were crayfish-free (they had not yet been stocked with crayfish). It is also possible

that exposure to adult trout, white suckers, sculpin and other predatory fishes that were too big to

enter the cages but had access to the uncaged control contributed to reduced control densities.

Finally, reduced control densities may not be biologically meaningful and may have resulted

from the chance selection of a control site with lower density relative to the enclosures.

During post-sampling, invertebrate densities in the treatments and uncaged control were

toward the upper end of the range reported for Pennsylvania streams and rivers (see Jackson et

al. 1994, Lieb 1998, Lieb and Carline 1999, Thomson et al. 2005, and Carline and Walsh 2007).

Exclosure densities were particularly high and greatly exceeded most reported values, which was

likely due to the exclusion of predatory crayfish and larger fish from the exclosures. Invertebrate

communities in the treatments were similar to that in the uncaged control and were dominated by

Chironimidae; other taxa typically comprised < 10% of the assemblage.

In running waters, predators typically decrease local benthic invertebrate density via

direct consumption, increased drift (predator avoidance), or both (Wooster et al. 1997). Declines

in the density of highly mobile taxa in response to predators are usually due to a combination of

24

predator avoidance and direct consumption, whereas declines in immobile taxa are usually due to

direct consumption (Wooster et al. 1997). In my study, the benthic invertebrate assemblage

inhabiting pool areas of Spruce Creek was dominated by immobile Chironomidae, which

accounted for 77±3% (mean±1SE) of the invertebrates collected from the cages and the control

during this study. For this reason, the declines in invertebrate density that I observed in Spruce

Creek were probably caused by the direct consumption of invertebrates by crayfish. Consumed

invertebrates appear to be readily assimilated, contributing significantly to crayfish growth and

production in Spruce Creek [D.A. Lieb, PSU and J.A. Freedman, Illinois Natural History Survey

(INHS), unpublished stable isotope data], as they do elsewhere (Momot 1995, Whitledge and

Rabeni 1997, Parkyn et al. 2001, Roth et al. 2006, Olsson et al. 2008, Giling et al. 2009). A

substantial portion of this crayfish production is then passed up the food chain to trout, especially

large individuals (Figure 2.3 and D.A. Lieb, PSU and J.A. Freedman, INHS, unpublished stable

isotope data). Thus, crayfish are functionally important in Spruce Creek, facilitating the transfer

of nutrients up through the food chain to fish (invertebrates→crayfish→trout), as has been

demonstrated in other systems (Rabeni 1992, Roell and Orth 1993, Momot 1995, Whitledge and

Rabeni 1997, Geiger et al. 2005).

The transfer of nutrients up through the food chain to trout is likely an economically

valuable service, because trout streams attract thousands of fishermen to central Pennsylvania

every year. These fishermen spend money during their visits boosting local economies. For

example, in 1988, the yearly economic value of a section of Spring Creek (Fisherman‘s Paradise)

that is comparable to the PSU Research Area and is located about 30 km from Spruce Creek was

estimated at about $44,000 per km (Shafer et al. 1993).

25

The results of this study clearly demonstrate the ecological importance of Spruce Creek‘s

crayfish assemblage and suggest that crayfish may benefit local economies by providing a

recreationally valuable fish species (brown trout) with forage. The growing realization that

crayfish are functionally important but highly vulnerable suggests that future crayfish

extirpations/extinctions are likely and that those losses may have far-reaching ecological

consequences on aquatic resources. For this reason, it is vital that natural resource managers and

policy makers recognize the value of native crayfish populations and take measures to preserve

them wherever possible.

Acknowledgments

I gratefully acknowledge the help of John G. Lieb, Vivian B. Lieb, Kristin Babcock, Adam

Smith, V. Malissa Mengel, and Dan Counahan during the fall 2002 experiment.

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32

Table 2.1. Comparison of invertebrate densities between treatments (enclosures vs

exclosures) and sampling periods (pre-sampling vs post-sampling) using a repeated-

measures, three-factor ANOVA with pair as a blocking factor.

Source d.f. MS F P

Pair 4 1.38 0.6 0.710

Treatment 1 3.10 6.6 0.063

Pair × Treatment 4 0.47 15.6 0.010

Sampling Period 1 7.93 3.8 0.122

Pair × Sampling Period 4 2.08 68.6 0.001

Treatment × Sampling Period 1 3.02 99.6 0.001

Error 4 0.03 - -

33

Figure 2.1. Map of the experimental pool in the lower reaches of Spruce Creek showing the

approximate positions of the cages, debris shields, and uncaged control during the caging

experiment.

Flow

80m

Debris

Shield

Cage

28m

16m

Control

34

Figure 2.2. Mean (±1SE) invertebrate densities on bricks collected from cages with crayfish

(enclosures, □), cages without crayfish (exclosures, ●), and an uncaged control (▲) prior to

adding crayfish to enclosures (pre-sampling) and 32 days after crayfish addition (post-sampling).

N=5 for the enclosures and exclosures and N=1 for the control.

0

1600

3200

Pre-sampling Post-sampling

Num

ber

in

ver

tebra

tes/

bri

ck

35

Figure 2.3. Percent of wild brown trout collected from the lower reaches of Spruce Creek that

had crayfish in their stomachs at the time of capture. Data presented for large trout, 275 mm in

total length (TL) (n=52), small trout, < 275 mm TL (n=157), and all trout combined (n=209). A

greater proportion of large trout had crayfish in their stomachs than did small trout (Chi-square

test, p<0.001).

0

10

20

30

40

<275mm ≥275mm All trout

% o

f tr

out

stom

achs

wit

h c

rayfi

sh

36

Chapter 3

The Discovery and Ecology of a Member of the Cambarus acuminatus Complex (Decapoda:

Cambaridae) in Valley Creek, Southeastern Pennsylvania

Modified from:

Lieb, D.A., R.F. Carline, J.L. Rosenberger, and V.M. Mengel. 2008. The discovery and ecology

of a member of the Cambarus acuminatus complex (Decapoda: Cambaridae) in Valley

Creek, Southeastern Pennsylvania. Journal of Crustacean Biology 28: 439-450.

Abstract

The Cambarus acuminatus complex is a poorly known group of crayfish species whose

range has traditionally been assumed to extend from the Patapsco River drainage in Maryland

southward to the Saluda River basin in South Carolina. During a recent crayfish survey of

southeastern Pennsylvania, I collected a member of the C. acuminatus complex [Cambarus

(Puncticambarus) sp.] from Valley Creek. Collections were made from several habitats [pools,

riffles, shallow lateral areas (SL), main-channel areas (MC)], and dominant substrate classes,

current velocity, and depth were recorded in each sampling area. These collections represent a

new crayfish record for Pennsylvania and the first documented occurrence of the C. acuminatus

complex north of the Patapsco drainage. Life history characteristics of the population of C. (P.)

sp. inhabiting Valley Creek are provided and their variation among habitats and seasons is

discussed. In pools, C. (P.) sp. density was negatively related to current velocity, depth, and %

37

sand, and positively related to % silt. In riffles, C. (P.) sp. density was negatively related to

current velocity. Comparisons among habitats indicated that C. (P.) sp. was abundant in SL but

was scarce in MC. Although MC tended to have faster current, greater depth, more sand, and less

silt than SL, other factors could have been responsible for the relative scarcity of C. (P.) sp. in

MC. More conclusively, there was a positive relationship between C. (P.) sp. density and %

cobble in MC of pools, suggesting that activities such as urbanization that result in sediment

deposition and burial of rocky substrates may have a negative effect on density in MC. Since MC

are important for large, reproductive individuals, reduced density in these areas may affect the

reproductive potential of the population. These findings indicate that Valley Creek supports an

unusual and potentially threatened crayfish population that requires further study and highlight

the need for additional fieldwork in the region.

Introduction

The C. acuminatus complex is a poorly known group of crayfish species whose range has

traditionally been assumed to extend from the Patapsco River drainage in Maryland southward to

the Saluda River basin in South Carolina (Hobbs, 1989). Published accounts of the complex are

limited to collections from Maryland, Virginia, North Carolina, and South Carolina (Meredith

and Schwartz, 1960; Hobbs, 1972, 1989; Taylor et al., 1996). Although the complex has not

previously been reported from Pennsylvania, much of what is known about the state‘s crayfish

fauna is dated and includes relatively few records from parts of southern Pennsylvania [see

Ortmann (1906) and Schwartz and Meredith (1960)], where members of the complex are most

likely to be found. In particular, substantial areas of southeastern (SE) Pennsylvania have never

been sampled for crayfish.

38

Although considerable taxonomic progress has been made in recent years with the

southern members of the complex, including the description of four new species from North

Carolina (Cooper, 2001; Cooper and Cooper, 2003; Cooper, 2006a, b), northern populations

remain virtually unknown [J. E. Cooper, North Carolina State Museum of Natural Sciences

(NCMNS), personal communication]. In fact, published information concerning the northern

populations is currently limited to that provided by Meredith and Schwartz (1960), who reported

C. acuminatus from 18 lotic sites located along the fall line (the transitional zone between the

Piedmont and Coastal Plain) between Baltimore, Maryland and Washington D.C., but provided

no additional information concerning the ecology of the species.

In early spring 2000, Jan Briede (Scientech, NES, Inc.) and Jamie Krejsa (Enviroscience,

Inc.) collected four unusual crayfish specimens from Valley Creek (Cr) within Valley Forge

National Historical Park (VFNHP) in SE Pennsylvania. Roger F. Thoma (Ohio State University

Museum) tentatively assigned those specimens to the C. acuminatus complex. If the

identifications are confirmed, they represent the northern-most occurrence of the complex in the

United States. As with other northern locations where members of the C. acuminatus complex

have been found, almost nothing is known about the crayfish fauna of Valley Cr.

Because land use changes (urbanization) and associated sedimentation and habitat

alterations threaten all the biota of Valley Cr (Kemp and Spotila, 1997) and are problematic for

crayfishes in general [see discussions in DiStefano et al. (2003a) and Westhoff et al. (2006)], it is

essential that data regarding the creek‘s crayfish fauna be acquired so that informed decisions

can be made about how to protect these animals. Management decisions must be based on the

best possible information because not only do they have the potential to affect the future of

Valley Creek‘s crayfish fauna but also that of a possible species of concern in Pennsylvania, the

39

queen snake (Regina septemvittata). The queen snake, which is found along Valley Cr within

VFNHP, is thought to be disappearing from parts of Pennsylvania (particularly the SE part of the

state) due to the adverse effects of pollution on its primary food source, crayfish (Hulse et al.,

2001). Urbanization is not the only threat to Valley Creek‘s crayfish fauna. In fact, exotic

crayfish such as the rusty crayfish (O. rusticus) are potentially an even greater concern, because

they have been identified as one of the biggest threats to native crayfish in North America

(Butler et al., 2003) and are abundant in several nearby streams, some of which are completely

devoid of native crayfish [D. A. Lieb, The Pennsylvania State University (PSU), unpublished

data].

Although this study is of obvious regional and taxonomic significance, the ecological

information provided in this paper should appeal to a much broader audience because, although

crayfish often have major direct and indirect effects on the structure and function of rivers and

streams (Huryn and Wallace, 1987; Hart, 1992; Creed, 1994; Rabeni et al., 1995; Usio, 2000;

Schofield et al., 2001; Stenroth and Nyström, 2003; Creed and Reed, 2004), the life histories and

habitat preferences of most species are unknown and are badly needed (Corey, 1988; Taylor et

al., 1996; Riggert et al., 1999; Hobbs, III, 2001; DiStefano et al., 2003a;Westhoff et al., 2006).

More specifically, although approximate lower thresholds have been reported for calcium (~5

mg/L) and pH (~5.5) and data on temperature, dissolved oxygen, salinity, and pollution

tolerances and refuge (e.g., cobbles, macrophytes) requirements are available for some crayfishes

(see Hobbs and Hall 1974, Lodge and Hill 1994, Nyström 2002), detailed habitat preference

studies have been conducted for few species. The objectives of this study were to: 1) determine if

a reproducing population of crayfish belonging to the C. acuminatus complex occurs in Valley

Cr, 2) conduct a comprehensive survey of Valley Cr within VFNHP and produce a list of all the

40

crayfish species that occur there, and 3) determine the basic life history characteristics,

reproductive status, and habitat preferences of the crayfish species that occur in Valley Cr within

VFNHP.


Study Area

Valley Cr, which is located in the Piedmont of SE Pennsylvania, drains about 64 km2 of

largely urbanized land in the Philadelphia suburbs. The creek consists of two main branches,

Valley Cr and Little Valley Cr, which combine and then flow for about 5 km before emptying

into the Schuylkill River (Figure 3.1). Crayfish sampling stations were located in the lower

reaches of Valley Cr within VFNHP. Owing mainly to the presence of the park, my sampling

stations are situated in what is perhaps the least disturbed section of the creek (Steffy and

Kilham, 2004). Because much of the creek‘s flow originates from limestone springs,

temperatures tend to be moderate (4-18 °C), and nutrient availability is generally high (Sloto,

1990). Additional information concerning Valley Cr and its biota are provided in Kemp and

Spotila (1997).

Crayfish Collections

I collected crayfish from four stations along Valley Cr (Figure 3.1). Each station

consisted of one riffle-pool sequence and averaged 64 m in length (range = 37-87 m). Within

stations, stream widths averaged 14 m (10-17 m) for pools and 12 m (6-18 m) for riffles; bottom

substrates were primarily cobble, gravel, sand, and silt. Large rocks (boulders), root masses, and

41

aquatic vegetation were uncommon in most areas. At each station, crayfish samples were

collected from four habitat types: shallow lateral areas of pools (SLP) and riffles (SLR) and

main-channel areas of pools (MCP) and riffles (MCR). SL were within 2 m of shore. MC were

3 m from shore. Each station was sampled during daylight hours on two occasions: spring (21-22

April) and fall (18-19 October) of 2003. Sampling occurred during baseflow conditions when

water clarity was high and the stream bottom was clearly visible.

Four collection techniques were employed during this survey. Seines (2.8 2.0 m bag

seines with 5 mm mesh) were tried in the spring but not the fall because, as was found by Brant

(1974), they often became snagged on various obstructions and were ineffective (0 crayfish

collected). Rectangular traps (~ 0.2 0.3 0.6 m) were baited with raw beef kidney and placed

overnight in pools and riffles at depths ranging from 0.3-1.2 m. Similar to the findings of Eng

and Daniels (1982), Rabeni et al. (1997), and DiStefano (2000), traps were not useful in Valley

Cr (a total of two crayfish captured during eight trap-nights) and were also not used in the fall.

Dipnets (hand collections) were tried in the spring (a total of two crayfish captured) but were

quickly abandoned because, similar to the results of Rabeni et al. (1997), they were inefficient

over large reaches relative to electrofishing gear. Single-pass electrofishing was the primary

collection method used during both the spring (347 individuals captured) and fall (262

individuals captured) and, as reported by Westman et al. (1978) and Rabeni et al. (1997), was

effective in collecting crayfish from all the major habitats present at my sampling stations. The

relative scarcity of large rocks, which for obvious reasons can be difficult to electrofish, likely

contributed to the effectiveness of electrofishing gear in this study.

Electrofishing collections were made in an upstream direction using a boat-mounted unit

(pulsed-DC current, 200-volt, Coffelt Electronics Company). Crayfish, which were often pulled

42

out from under cover (cobbles, logs) during sampling, were involuntarily drawn to the anode [as

described by Westman et al. (1978)] and netted. In most cases, four separate areas at each station

(one area per habitat type) were sampled with electrofishing gear during each season. The

physical characteristics of electrofished areas are listed in Table 3.1. Electrofishing data provided

indices of crayfish density in each sampling area (individuals collected/m2). Care was taken to

ensure consistent effort among habitat types, seasons, and stations (especially in terms of the

time spent sampling per unit of stream bottom).

In the spring, human error and equipment failure prevented me from estimating density in

some areas. For example, at station 1, specimens from SLR and MCR (95 total) were

inadvertently placed in the same jar, thereby preventing the calculation of separate density

estimates for those locations. Additionally, equipment failure prevented the collection of crayfish

from SLR of station 2. Thus, in the spring, estimates of crayfish density were lacking for SLR of

stations 1 and 2 and MCR of station 1.

After collection, crayfish were preserved in 95% ETOH and transported to the laboratory

where they were identified and carapace length (CL; the distance from the tip of rostrum to the

posterior median margin of the carapace) and male reproductive state (form I, II) determined

following Hobbs (1972). Females were inspected for eggs and young. My identifications were

confirmed by John E. Cooper of the NCMNS and Raymond W. Bouchard of the Academy of

Natural Sciences of Philadelphia. Voucher specimens were deposited in the crustacean collection

of the NCMNS, Raleigh, North Carolina (catalogue numbers 24749-24753), the Ohio State

University Museum (catalogue numbers 6487-6491), Columbus Ohio, and the Carnegie Museum

of Natural History, Pittsburgh, Pennsylvania (catalogue numbers C2005-24-27).

43

Habitat Measurements

Dominant substrate classes, depth, and current velocity were recorded along transects

within each electrofished area. Transects were oriented perpendicular to flow and were evenly

spaced within each sampling area. In the spring, there were generally 5 or 6 transects per

sampling area. Exceptions were the MCR of stations 2, 3 (no habitat data available), and 4 (only

two transects). One set of habitat measurements (substrate, depth, flow) was made at the center

of each transect. In the fall, there were 3 or 4 transects per sampling area. Within SL areas,

measurements were made at locations ≤ 0.5, 1, and 2 m from shore along each transect. Within

MC areas, 5-7 equally-spaced sets of measurements were made along each transect. Current

velocity was measured at 0.6 of the distance from the water surface to the stream bottom using a

portable flow meter (Marsh-McBirney Flowmate 2000). Bottom substrates were assessed

visually and the two dominant substrates recorded. Approximately 0.9 m2 of stream bottom was

assessed at each location. Substrates were assigned to size classes (silt, sand, gravel, cobble,

boulder) based on Platts et al. (1983).

Data Analysis

Electrofishing data were used to compare C. (P.) sp. density between main habitats (pool

vs. riffle) and sub-habitats (SL vs. MC) using a repeated measures, 4-factor (station, main

habitat, sub-habitat, season), strip-plot ANOVA with station as a blocking factor [as described in

Steel and Torrie (1980)]. A repeated measures analysis (season terms included in the model) was

used because the same areas were sampled on two occasions (spring and fall). A strip-plot (also

called a split-block) design allowed me to account for the fact that, within each block, plots

(pools, riffles) and subplots (SL, MC) were adjacent [see pg. 390 of Steel and Torrie (1980)].

44

Station×main habitat×season and station×sub-habitat×season interaction terms could not be

included in my model due to missing data (see ‗Crayfish Collections‘ section), which resulted in

insufficient degrees of freedom. Thus, F-tests for sub-habitat×season and main habitat×season

are approximate (but the best that can be done) because denominators consisted of the error

mean square (MSE) instead of the more appropriate 3-way interaction, e.g., station×main

habitat×season, mean square. Other F-tests were carried out as described in Steel and Torrie

(1980).

Electrofishing data were also used to determine if there were relationships between C.

(P.) sp. density and microhabitat characteristics (current velocity, depth, % silt, % sand, %

gravel, % cobble, % boulder) using correlation analysis. Since the primary objective of these

analyses was to determine whether or not there was a relationship between microhabitat and

density (regardless of the form of the relationship), I used Spearman‘s rank correlations (rs) to

test for associations between variables following Ott (1992) and Mendenhall and Beaver (1994).

Because microhabitat measurements were made at multiple locations within each electrofished

area, but only one density estimate was available for each area (the entire area was

electrofished), microhabitat data were summarized prior to correlation analysis. For depths and

current velocities, mean values were calculated. For substrate characteristics, the percent of

locations where a particular substrate class, e.g., cobble, was dominant or co-dominant was

determined.

Pools and riffles were analyzed separately for each microhabitat characteristic. MCP

were of particular interest and were also analyzed separately because it appeared that those areas

were often filled with fine sediments (silt, sand) of rather recent origin and therefore may be

susceptible to sedimentation from ongoing urbanization of the watershed. Spring and fall data

45

were pooled prior to analysis because relationships in the spring were similar to those in the fall

and sample sizes in individual seasons were relatively low (riffle n = 3, pool n = 8, and MCP n =

4 in spring; riffle n = 8, pool n = 8, and MCP n = 4 in fall).

More complicated and potentially more definitive microhabitat analyses (multiple

regression) were not conducted because relationships between several of the microhabitat

characteristics (% silt, % sand, current velocity, depth), and density were confounded by the

effects of sub-habitat (see ‗Habitat Associations‘ section for additional comments). An obvious

solution would be to analyze each sub-habitat type separately (separate multiple regressions for

SLP, MCP, SLR, and MCR). Unfortunately, not enough data were available for separate

analyses (Zar, 1999). Additionally, simple correlations were adequate because the intent of my

microhabitat analyses was to identify potentially important relationships to be explored further

with additional data or experiments.

All C. (P.) sp. specimens were used to compare size (CL) between seasons (spring vs.

fall), habitats (pool vs. riffle and lateral vs. main channel), and sexes (male vs. female) and to

compare sex ratios, and occurrence of form I males (male I) between seasons and habitats. Size

comparisons were completed using a repeated measure, strip-plot ANOVA with station as a

blocking factor (described previously). An additional factor (sex) was included to compare male

and female size. Three-way interaction terms could not be included in the model due to missing

data and the collection of only one sex from some locations, which resulted in insufficient

degrees of freedom. Thus, F-tests for all 2-way interaction terms, e.g., sub-habitat×season, are

approximate (but the best that can be done) because denominators for those tests consisted of the

MSE instead of the more appropriate 3-way interaction terms, e.g., station×sub-habitat× season.

Other F-tests were carried out as described in Steel and Torrie (1980). Mean sizes were used in

46

these analyses because multiple crayfish were collected (and measured) from each sampling

area. I weighted mean sizes by the number of crayfish collected (n) because n varied among

habitat types, stations, and seasons. Sex ratio and male I comparisons were carried out using chi-

square tests.

Due to human error and equipment failure, life history data (size, sex ratio, male I) were

not available for some areas (the same areas which also lacked density estimates). Further, one

C. (P.) sp. could not be measured accurately or sexed (most of its abdomen missing) and was not

included in life history analyses. An additional four specimens could also not be measured

accurately due to damage and were not included in size analyses.

For size and density analyses, least squares means (LSM; also sometimes referred to as

adjusted marginal means) instead of simple means are reported to avoid the potential bias caused

by the unequal number of observations in the cells of my multi-way classification of the data

(Milliken and Johnson, 1992). For all analyses, p-values < 0.05 were considered significant and

Minitab Release 13 (Minitab, Inc., State College, Pennsylvania) was employed. Results were

confirmed using SAS version 9.1 (SAS Institute, Inc., Cary, North Carolina).


Taxonomy

My surveys yielded two species of crayfish. One of those species, C. b. bartonii, is

common throughout much of the state, while the other, a member of the C. acuminatus complex

[referred to as C. (P.) sp.], has never before been reported from Pennsylvania. Although I will

not be able to assign a species name to the C. (P.) sp. specimens until the complex is completely

diagnosed (J. E. Cooper, NCMNS, personal communication), they are almost certainly not true

47

C. acuminatus, as originally described by Faxon (1884), because the native range of true C.

acuminatus is likely limited to the Saluda River Basin in South Carolina (Hobbs, 1969; J. E.

Cooper, NCMNS, personal communication). Additionally, the Valley Cr specimens are clearly

not one of the four recently described species in the complex, and are therefore probably a new

species that has not yet been described (J. E. Cooper, NCMNS, personal communication).

Although one might argue that this paper should wait until a species name can be

attached to the Valley Cr specimens, that is likely many years away (J. E. Cooper, NCMNS,

personal communication), and preliminary data from ongoing surveys of SE Pennsylvania

suggest that C. (P.) sp. may be native to Pennsylvania and, due to its limited range within the

state (likely restricted to Valley Cr and several nearby streams) and proximity to urban centers

and populations of rusty crayfish, is highly threatened (Lieb et al., 2007). Thus, the data provided

in this paper are needed to ensure the continued viability of one of the few populations of C. (P.)

sp. in Pennsylvania. Further, aside from a few C. b. bartonii, the specimens I have collected from

Valley Cr are all the same species, i.e., I am not lumping multiple species under the name C. (P.)

sp. (J. E. Cooper, NCMNS, personal communication). Thus, because I have properly cataloged a

range of specimens at several museums, it will be possible, in the future, to attach a species name

to my specimens and the information provided in this paper can then easily be attributed to that

species.

Community Composition

My surveys indicate that C. (P.) sp. is the dominant crayfish species in Valley Cr. Of the

613 crayfish specimens collected during the 2003 surveys, 603 were C. (P.) sp., 9 were C. b.

bartonii, and 1 could not be identified to species (appeared to share characteristics of the two

48

species, may have been a hybrid). The C. (P.) sp. collections included large numbers of juveniles

and adults, a wide range of sizes, and both sexes (Figure 3.2) indicating that the species is

established and is reproducing in Valley Cr. In contrast, C. b. bartonii was uncommon, making

the reproductive status of this species in Valley Cr uncertain. In fact, it is possible that the C. b.

bartonii collected from Valley Cr were washed in from upstream tributaries during rain events,

which often result in rapid discharge increases in Valley Cr (United States Geological Survey,

unpublished streamflow data).

Life History Characteristics

Size Structure. — Although C. (P.) sp. collections were devoid of females with

attached ova or young (reproductive females), juveniles and adults of both sexes and all sizes

were well represented. In both the spring and fall, it was evident that the size structure of the

population was biased toward small individuals [> 80% of the individuals collected were 9-23

mm carapace length (CL)] resulting in length-frequency distributions that are skewed to the right

(Figure 3.2). An obvious break in the fall length-frequency histogram suggests the presence of at

least two distinct size classes at that time [9-18 mm CL (peak at 14) and ~ 23-38 mm CL (peak at

27)]. Size classes were less distinct in the spring, although peaks were observed at 18-20 mm CL

and 34-35 mm CL. The presence of large numbers of very small (≤ 14 mm CL) individuals in the

fall but not the spring collections suggests that substantial juvenile recruitment occurred

sometime between the end of April and the end of October, which agrees with the general life

history of many cambarid crayfishes (Hobbs III, 2001).

Males tended to be larger (LSM = 21.7 mm CL) than females (LSM = 19.7 mm CL), as is

often the case for crayfish (Reynolds, 2002), but differences were not significant (NS) (Table

49

3.2). This result was consistent across stations, sub-habitats, and main habitats, as indicated by

the lack of significant interactions between sex and those factors. In contrast, I found a

significant sex×season interaction, which was driven by the fact that males tended to be larger

than females in one but not both seasons (Figure 3.2). Specifically, in the spring males were, on

average, 22% larger than females (male LSM = 22.1 mm CL, female LSM = 18.1 mm CL);

whereas, in the fall male and female sizes were nearly identical (male LSM = 21.3 mm CL,

female LSM = 21.2 mm CL). Stated another way, male size was similar across seasons, whereas

females tended to be smaller in the spring than in the fall. These results are expected if large,

mature females with attached ova and young, which are typically sequestered and difficult to

collect (see subsequent ‗Sex Ratio‘ and ‗Gear Bias‘ sections), were present in Valley Cr at the

time of the April but not the October collections. The absence of large, reproductive females

from the April collections would have reduced the average size of the females collected during

that time. This explanation seems plausible given that, for cambarid crayfishes, females with

attached eggs and young are typically present in spring but not fall (Hobbs III, 2001). Although

these results make biological sense, the p-value for the season×sex interaction was not

exceptionally small (0.02) and exact F-tests for interaction terms were not possible (see ‗Data

Analysis‘ section), indicating that additional studies are needed to confirm the importance of

sex×season interactions on C. (P.) sp. size.

Differences in size were readily apparent among some, but not all habitat types. For

example, main-channel areas supported much larger individuals (LSM = 25.1 mm CL) than

lateral areas (LSM = 16.2 mm CL), but riffles and pools supported C. (P.) sp. of similar size

(pool LSM = 20.3 mm CL, riffle LSM = 21.0 mm CL) (Table 3.2). Although interaction terms

should be interpreted cautiously, the subhabitat×season interaction term was highly significant

50

(p-value < 0.001), indicating that the magnitude of the difference between sub-habitats (larger

individuals in the main channel than in lateral areas) varied seasonally (Figure 3.2). More

specifically, in the fall, individuals in the main channel were, on average, 93% larger than those

in lateral areas (main channel LSM = 28.0 mm CL, lateral LSM = 14.5 mm CL), whereas, in the

spring, main-channel individuals were, on average, only 23% larger than those in lateral areas

(main channel LSM = 22.2 mm CL, lateral LSM = 18.0 mm CL). Phrased differently,

individuals inhabiting main-channel areas were smaller in spring than fall, whereas in lateral

areas individuals were larger in spring than fall. Although this interaction is probably best

explained by the substantial influx of very small individuals, which tend to prefer lateral areas, in

the fall, other factors such as the scarcity of large, reproductive females, which tend to prefer

main-channel areas, in the spring could also have contributed to the subhabitat×season

interaction. In contrast, sub-habitat differences were consistent across stations, main habitats, and

sexes, as indicated by the lack of significant interactions between sub-habitat and those factors.

Similarly, mainhabitat results (no difference between pools and riffles) were consistent across

stations, sub-habitats, seasons, and sexes, as indicated by the lack of significant interactions

between main habitat and those terms.

There was a subtle trend toward the collection of smaller individuals at upstream

compared to downstream stations; however a significant station effect was not found (LSM for

stations 1, 2, 3, and 4 = 18.6, 20.4, 20.4, and 23.3 mm CL, respectively) (Table 3.2). No

significant interactions between station and the other factors were found indicating that size was

similar across stations regardless of the main habitat, sub-habitat, season, or sex considered.

Seasonal comparisons showed that size in the spring (LSM = 20.1 mm CL) was not different

from that in the fall (LSM = 21.2 mm CL). Seasonal effects were consistent across stations and

51

main habitats (station×season and main habitat×season not significant) but varied among sub-

habitats and sexes (sub-habitat×season and sex×season significant, see above).

My finding that small individuals dominated collections of C. (P.) sp. in Valley Cr is in

agreement with studies of other crayfish species (Jordan et al., 1996; Englund and Krupa, 2000;

DiStefano et al., 2003a) and is not unexpected given that crayfishes generally exhibit a type III

(concave) survivorship curve with mortality decreasing markedly with age (size) (Hobbs III,

2001). Although I was able to roughly determine the timing of recruitment for C. (P.) sp. in

Valley Cr (sometime between the end of April and the end of October) and distinguish at least

two size classes in each season (especially in the fall), a more complete determination of the life

cycle of C. (P.) sp. in Valley Cr would have required additional collections in other seasons

(summer, winter) and at more frequent intervals (monthly or bimonthly), which was beyond the

scope of this study.

While no data, other than that in this paper, are available concerning the size-habitat

relationships of any member of the C. acuminatus complex, studies of other species tend to

concur with my finding that deep, main-channel areas support larger individuals than shallow,

lateral areas (Taylor, 1983; Butler and Stein, 1985; Rabeni, 1985; Creed, 1994; DiStefano et al.,

2003a). Englund and Krupa (2000) explored the cause of this pattern and found that the

distribution of small crayfish shifts to shallow water in the presence of fish predators. This result

suggests that brown trout (Salmo trutta), which consume crayfish (Bachman, 1991; Nyström et

al., 2006; Figure 2.3) and are common in Valley Cr (Kemp and Spotila, 1997), may be, at least

partly, responsible for the tendency of small C. (P.) sp. to occupy shallow, lateral areas in Valley

Cr.

52

In contrast, much less is known about differences in crayfish size between pools and

riffles and few generalities are currently possible. In one of the few available studies, DiStefano

et al. (2003a), who worked with an assemblage of crayfish composed mainly of Orconectes

luteus, Orconectes ozarkae, and Orconectes punctimanus, showed that the ratio of adult density

to young-of-the-year (YOY) density was much greater in riffles than in pools, indicating that

crayfish CL was probably greater in riffles than in pools in their study. This result confirms

earlier, less direct work by Rabeni (1985), who found that O. luteus YOYs preferred low-

velocity areas, whereas adults preferred high-velocity areas; again suggesting that individual size

in riffles (high-velocity areas) is greater than that in pools (low-velocity areas) for O. luteus. In

contrast, Gore and Bryant (1990) found that YOY Orconectes neglectus preferred high-velocity

areas with cobble (generally found in riffles), whereas adults preferred low-velocity, macrophyte

beds (generally found in pools). Therefore, it seems likely that individual size in pools is greater

than that in riffles for O. neglectus. Thus, large individuals were concentrated in riffles for O.

luteus, O. ozarkae, O. punctimanus, in pools for O. neglectus, and were spread equally among

pools and riffles for C. (P.) sp. suggesting that, for crayfishes, there are species-specific

differences in how juveniles and adults are distributed among certain habitat types (riffles and

pools).

Although the absence of reproductive females from my collections may have contributed

to the interactions observed (sex×season, sub-habitat×season), other results were probably little

affected. For example, the collection of reproductive females would, undoubtedly, have

increased the average size of the individuals in the main channel (because reproductive

individuals tend to be large, and large individuals prefer main-channel areas), strengthening my

finding that individuals in the main channel are larger than those in lateral areas. This argument

53

is based on several assumptions. First, I assume that reproductive females tend to be large, which

is likely true given that many cambarid crayfishes do not reach maturity until their second or

even third year of life (Hamr and Berrill, 1985; Corey, 1988; Hobbs III, 2001). Second, I assume

that large reproductive females are distributed similarly to large nonreproductive females, i.e.,

large reproductive females prefer main-channel areas. Anecdotal support for this assertion is

provided by recent surveys of nearby streams, which resulted in the collection of a few

reproductive female C. (P.) sp., all of which were found in main-channel areas (D. A. Lieb, PSU,

unpublished data).

Sex Ratio. — Across seasons and habitat types, the sex ratio of C. (P.) sp. was male-

biased, although the bias was not extreme [1.2:1 (male:female), n = 602, Chi-square test, p =

0.01]. When individual seasons or habitat types were considered, deviations from 1:1 were

sometimes larger. For example, there was a male bias in the spring (1.4:1, n = 348, p = 0.002),

but not the fall (1.02:1, n = 254, p = 0.90). Similarly, when habitats were considered

individually, riffles were male-biased (1.4:1, n = 201, p = 0.02), whereas pools were not (1.1:1, n

= 401, p = 0.18). Partitioning the data between main-channel and lateral areas showed a male

bias in the main channel (1.6:1, n = 91, p = 0.03), but not in lateral areas (1.1:1, n = 416, p =

0.49).

Although the sex ratios of most crayfish populations are believed to be 1:1 (Reynolds,

2002), a number of authors have reported male-biased catches during at least part of the year

(Capelli and Magnuson, 1983; Taylor, 1983; Fenouil and Chaix, 1985; Van Den Brink et al.,

1988; Ackefors, 1999; Alekhnovich et al., 1999; Frutiger et al., 1999; Flinders and Magoulick,

2005) and some attributed this bias to the use of a particular collection technique, e.g., trapping

54

tends to be biased toward males. I also found that C. (P.) sp. catches were male-biased during

part of my study (in the spring but not the fall) and attribute this, at least in part, to the lack of

reproductive females in my collections, but not to my choice of collection techniques (see ‗Gear

Bias‘ section for further discussion).

The generality of my finding that sex ratios vary among habitats in Valley Cr (male bias

in riffles and main-channel areas but not in pools and lateral areas) is unknown at this time

because few data are available. However, variation in sex ratios among habitats in Valley Cr is

not unexpected given that the biology of male and female crayfish often differs, especially

during the breeding season. For example, females often feed less than males during the egg-

bearing stage of their reproductive cycle (Hopkins, 1967; Abrahamsson, 1971; Brewis and

Bowler, 1982; Taylor, 1983; Skurdal and Qvenild, 1986; Pursiainen et al., 1987), which

ultimately may result in males and females selecting habitats based on different criteria during

parts of their life cycle, e.g., food availability may be a higher priority for males than females

during egg-bearing. Alternatively, male-biased catches in particular habitats could have been

due, at least in part, to difficulties in collecting reproductive females. For example, if

reproductive females favored particular habitats, but were deeply burrowed into the substrate and

were inaccessible, then male-biased catches would be expected in those areas.

Form I Males. — During this study, form I males only accounted for 7% of the total C.

(P.) sp. catch. The contribution of form I males to the catch was consistent across seasons (8% in

the spring and 6% in the fall) (Chi-square test, p =0.42), but not habitats. For example, form I

males accounted for a higher proportion of the catch in riffles (10%) than in pools (6%) (p =

0.04), and a higher proportion of the catch in main-channel areas (26%) than in lateral areas (3%)

55

(p < 0.001). Form I males were particularly well represented in main-channel riffle collections,

comprising 53% of the catch in those areas. However, overall abundance in those areas was low

[only 19 of 603 C. (P.) sp. were collected there].

My finding that form I male C. (P.) sp. comprised little of the total catch in Valley Cr

was expected given the results of other studies. For example, of the > 6000 specimens belonging

to five different species collected by Flinders and Magoulick (2005), < 400 were form I males (<

6% of the total catch). Studies by Corey (1988) and Riggert et al. (1999) with three other species

also showed that form I males were rarely collected during some seasons.

Gear Bias. — Although gear bias is a concern when studying the life history

characteristics of any species, and has the potential to affect crayfish collections, the results of

Westman et al. (1978) and Rabeni et al. (1997) suggest that unlike other collection methods,

which tend to be highly biased (traps favor large males; quadrant samplers favor juveniles)

electrofishing is an effective method for collecting crayfish of all sizes and life stages (even

reproductive females) from a variety of habitats, even where there is heavy cover. Westman et al.

(1978) cautioned that electrofishing was not effective in murky waters or depths 0.8 m;

however, water clarity in Valley Cr was high throughout this study and depths 0.8 m were

rarely encountered (only 3% of my depth measurements exceeded 0.8 m, Table 3.1). Based on

this information, my own observations (see ‗Methods‘), and the fact that electrofishing gear has

been used in similar studies of other large-bodied, freshwater crustaceans [Australian shrimps:

Richardson and Cook (2006)], it is tempting to conclude that electrofishing is completely

unbiased. However, the fact remains that females with attached ova or young were not collected

56

during this study, which may have biased my collections toward males (especially in the spring

when reproductive females are expected).

Studies of other members of the C. acuminatus complex suggest that this bias likely had

nothing to do with gear type and was probably due to the fact that female members of the

complex are extremely difficult to catch during parts of their reproductive cycle. For example,

despite extensive collections of the complex (four species, > 800 individuals) from a variety of

locations by a variety of collectors (presumably using a variety of sampling devices), only two

females with attached young and one with attached ova have been reported from North Carolina

(Cooper, 2001; Cooper and Cooper, 2003; Cooper, 2006a, b). Similar results (few reproductive

females collected) for a number of other crayfish species, collected using a variety of methods

(dipnets, kicknets, quadrant samplers, hand collections; Fenouil and Chaix, 1985; Hamr and

Berrill, 1985; Corey, 1988; Flinders and Magoulick, 2005), provide additional evidence that

male-biased catches in Valley Cr were not due to the use of electrofishing gear.

Habitat Associations

Comparisons among habitats revealed that C. (P.) sp. density was much higher in lateral

(LSM = 0.26 individuals/m2) than in main-channel areas (LSM = 0.02 individuals/m

2) (Table

3.3). Density of C. (P.) sp. also tended to be higher in pools (LSM = 0.17 individuals/m2) than in

riffles (LSM = 0.10 individuals/m2), but differences were NS. Density of C. (P.) sp. in the spring

(0.16 individuals/m2) was similar to that in the fall (0.12 individuals/m

2). C. (P.) sp. density was

also similar among stations (LSM for stations 1, 2, 3, and 4 = 0.15, 0.12, 0.16, and 0.13

individuals/m2, respectively) suggesting that, at least within my study area, there is little

longitudinal (upstream-downstream) variation in the abundance of this species. No significant

57

interactions were found, indicating that these results were consistent across habitats (sub and

main), seasons, and stations. Although few C. (P.) sp. were found in the main channel, the

individuals present were on average 55% larger than those found in lateral areas, suggesting that

differences in biomass between main-channel and lateral areas may not be as large as differences

in density.

Although the density values reported above likely underestimated actual density because

multiple electrofishing passes are typically required to collect all the crayfish from a given area

(Westman et al., 1978; Rabeni et al., 1997; D. A. Lieb, PSU, unpublished data), comparisons

among habitats, seasons, and stations were probably little affected by this bias because my

sampling procedures were consistent throughout the study (particularly in terms of effort). My

finding that C. (P.) sp. density in lateral areas was much greater than that in the main channel

was probably particularly robust to any such bias because smaller-scale, more intensive studies

elsewhere in Pennsylvania indicate that additional electrofishing passes (beyond the initial pass)

substantially increase the catch of small crayfish (particularly in lateral areas; D. A. Lieb, PSU,

unpublished data). Thus, actual differences in density between lateral and main channel areas

were likely even greater than those I documented. More generally, my densities can be thought

of as catch-per-unit-effort values (CPUE; effort standardized by the area sampled and time),

which are measures of abundance that have been successfully used to determine habitat

preferences in a wide range of aquatic species [see Lazzari et al. (2003), Barko and Hrabik

(2004), Jordan et al. (2004), and Wallace et al. (2006) for examples]. Additional multiple-pass

removal studies in Valley Creek may allow my values to be converted to actual densities in the

future (by determining the % of the total population that is captured during the first pass).

58

Substrate analyses revealed that there was a positive relationship between C. (P.) sp.

density and the prevalence of cobble (% cobble) in main-channel areas of pools (rs = 0.76, p <

0.05; Figure 3.3). Relationships between other substrate characteristics (% sand, % silt, % gravel,

% boulder) and density were NS. When main-channel and lateral data were combined, there was

a negative relationship between density and % sand (rs = -0.57, p < 0.05; Figure 3.4) and a

positive relationship between density and % silt (rs = 0.62, p < 0.05) in pools. Relationships

between other substrate characteristics (% gravel, % cobble, % boulder) and density were NS.

Analyses with riffle data (mainchannel and lateral data combined) did not reveal any significant

relationships between density and any substrate characteristic.

Although significant, relationships between density and substrate in pools (main-channel

and lateral data combined) should be viewed cautiously because sampling locations where

crayfish and silt were abundant and sand was scarce were mainly found in lateral areas, whereas

locations where crayfish and silt were scarce and sand was abundant were generally in the main

channel (Figure 3.4). Thus, although it is tempting to conclude that sand is negatively related and

silt positively related to density in pools, I cannot rule out the possibility that the relationship is

driven by the fact that main-channel areas have lower density than lateral areas naturally, i.e.,

regardless of whether sand and silt are present or not. The fact that lateral areas appeared to have

higher density than main-channel areas even when sand was abundant and silt was scare (see two

data points where > 50% of the lateral areas are sand and one data point where < 15% of the

lateral area is silt in Figure 3.4) suggests that, although the absence of sand and prevalence of silt

may contribute to higher density in lateral areas, other factors are likely also important.

Experimental studies (sand and silt either added or removed) or additional collections in main-

channel areas where sand is scarce and silt is abundant and in lateral areas where sand is

59

abundant and silt is scarce are needed to clarify the relationship between density and substrate

characteristics in pool areas of Valley Cr.

There was no relationship between density and either current velocity or depth in the

main-channel areas of pools. However, when main-channel and lateral data were combined,

there was a negative relationship between density and both current velocity (rs = -0.72, p <

0.005; Figure 3.4) and depth (rs = -0.58, p < 0.05) in pools and between density and current

velocity in riffles (rs = -0.81, p < 0.005; Figure 3.5). Although these relationships are strong, they

should be viewed cautiously because sampling locations with high density, low current velocity,

and shallow water were mainly found in lateral areas, whereas locations with low density, high

velocity, and deep water were generally in the main channel (Figure 3.4, 3.5). Thus, the situation

is analogous to that discussed previously for sand and silt. Regardless, C. (P.) sp. was completely

absent from areas where average flows exceeded about 0.50 m/s, suggesting that some fast-

current areas of Valley Cr are unsuitable for this species. These areas may be particularly

dangerous during spates when flows increase rapidly in Valley Creek (United States Geological

Survey, unpublished streamflow data), potentially dislodging and killing crayfish (see Nyström

2002 and references within).

Within my study area, I found a strong negative relationship between crayfish density and

depth in pools; however, this result may not apply to all areas of Valley Cr. This is because

relationships between crayfish density and depth may be affected by the presence of predatory

fish such as brown trout, and in some cases relationships may shift from strongly negative in the

presence of predatory fish to strongly positive in the absence of predatory fish (Englund, 1999).

Therefore, in reaches of Valley Cr where brown trout are rare [upstream, headwater areas; see

60

Kemp and Spotila (1997)] I may find a different relationship than I found in downstream

locations where brown trout are common (my study area).

Although C. (P.) sp. is abundant in the lateral areas of Valley Cr, where the water is

shallow, current velocity is low, sand is scarce, and silt is abundant, my results can only suggest

associations and cannot determine causality. This is because any number of other factors, such as

the prevalence of food resources and woody debris in lateral areas, competitive interactions, or

the presence of predatory fish in main-channel areas could have been responsible for the

macrohabitat associations observed [see Rabeni (1985) and DiStefano et al. (2003a) for thorough

discussions of many of these possibilities]. Given the flashy nature of Valley Creek‘s

hydrograph, root masses, which occur in lateral areas, may also be important because tree roots

afford some crayfish species protection from floods (Smith et al., 1996).

Whatever the cause, it is clear that C. (P.) sp. density was much higher in shallow, lateral

areas than in the main channel during both the spring and the fall sampling periods and that this

difference in density was primarily driven by the preference of small individuals (which

dominated my collections) for shallow, lateral areas. This result adds to a growing list of stream-

dwelling crayfishes, which, as juveniles, show a distinct preference for shallow, lateral areas

(Butler and Stein, 1985; Creed, 1994; DiStefano et al., 2003a).

One might argue that the lack of reproductive females in my collections reduced densities

in the main channel relative to lateral areas (because reproductive females are expected to select

main-channel areas; see ‗Size Structure‘ section); however, their absence certainly did not result

in differences in density as large as I observed (> an order of magnitude). This is because

crayfishes are characterized by high juvenile mortality with few individuals surviving to

reproductive age (Hobbs III, 2001). Thus, the absence of reproductive females, which probably

61

account for a minor proportion of overall density in the main channel, likely had a negligible

effect on my results. Further, my finding that lateral densities were greater than main-channel

densities in both the spring and fall [sub-habitat×season interaction NS (p = 0.595)] would not be

expected if my results were due to the absence of reproductive females. Instead, because

reproductive females should be present in the spring but not the fall (see Hobbs III, 2001),

differences in density between habitats should have been apparent in the April but not the

October collections resulting in a significant sub-habitat×season interaction.

Although I was unable to detect a statistical difference in crayfish density between pools

and riffles, as was found by DiStefano et al. (2003b), my results are qualitatively similar to theirs

(higher densities in pools than in riffles). The much larger sampling effort (> 60 × more samples

collected) of DiStefano et al. (2003b) likely provided them with far more statistical power than I

was able to achieve and thus a much higher probability of detecting differences between pools

and riffles.

Although I cannot say for certain why C. (P.) sp. densities were higher in lateral areas

than in the main channel, I do know that there was a positive relationship between density in

main-channel areas and prevalence of cobble in those areas, suggesting that activities such as

road construction and development, which result in sediment deposition and burial of rocky

substrates, may have a negative effect on the density of C. (P.) sp. in the main channel [see

similar, although less specific, concerns echoed by DiStefano et al. (2003a) and Westhoff et al.

(2006)]. Cobble habitats may be preferred because they have the potential to reduce cannibalism

and provide protection from predatory fishes such as brown trout (see Lodge and Hill 1994 and

Nyström 2002). Since main-channel areas are particularly important for large, reproductively

62

mature individuals (see ‗Life History‘ section), reduced density in the main channel may affect

the reproductive potential of the population.

Conservation Status and Future Directions

The discovery of a reproducing population of C. (P.) sp. in Valley Cr is noteworthy

because it is the first documented occurrence of any member of the C. acuminatus complex north

of the Patapsco River basin in Maryland (Figure 3.1) and as such represents a new crayfish

record for Pennsylvania. Of further interest, no member of the subgenus Puncticambarus, which

includes the C. acuminatus complex, had previously been found in eastern Pennsylvania.

Although efforts to determine the range of C. (P.) sp. in Pennsylvania are not yet complete,

preliminary results suggest that it is likely restricted to Valley Cr and several nearby streams and

may be native to Pennsylvania (D. A. Lieb, PSU, unpublished data). Similar studies in

neighboring states, where members of the C. acuminatus complex are known to occur

(Maryland, Virginia), are needed to determine the complete range of the species. The

conservation status of the species depends critically on this information because, if it is a narrow

endemic that is found only in SE Pennsylvania, then it may be threatened on the federal level;

however, if it has a broader distribution that includes locations in other states, then it may only

be threatened on the state level. Regardless, because C. (P.) sp. is only known from a few

locations in Pennsylvania, all of which are threatened by urbanization and rusty crayfish (D. A.

Lieb, PSU, unpublished data), regulatory action may be necessary to prevent its extirpation from

the state.

63

Acknowledgements

The National Park Service supported this work. Thanks go to John F. Karish, Nellie

Bhattarai, Brian Lambert (deceased), Adam Smith, and Paula Mooney for their contributions to

this study. Raymond W. Bouchard, Ted R. Nuttall, Eric S. Long, John F. Karish, Matt M.

Marshall, and two anonymous reviewers provided helpful critiques of the manuscript. I also

thank John E. Cooper and Raymond W. Bouchard for verifying my identifications and for many

informative discussions regarding the C. acuminatus complex. Lastly, I thank Jan Briede and

Jamie Krejsa for collecting 4 unusual crayfish from Valley Cr in 2000 and Roger F. Thoma for

recognizing that they belonged to the C. acuminatus complex, providing the impetus for this

study.

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72

Table 3.1. Physical characteristics of electrofished areas in Valley Creek. Mean values (

1SE) are reported for each habitat type [shallow lateral areas of riffles (SLR) and pools

(SLP) and main-channel areas of riffles (MCR) and pools (MCP)] and were calculated by

pooling data from the four sampling stations and two seasons (spring and fall). Sample

sizes are provided in parentheses. Data were collected on 21-22 April and 18-19 October

of 2003.

Habitat type Depth (m) Velocity (m/s) Area (m2)

SLR 0.12 ± 0.02 (67) 0.11 ± 0.03 (58) 67.2 ± 19.2 (6)

SLP 0.26 ± 0.02 (99) 0.05 ± 0.01 (94) 126.1 ± 13.8 (8)

MCR 0.23 ± 0.01 (98) 0.51 ± 0.03 (100) 156.8 ± 46.0 (7)

MCP 0.45 ± 0.02 (132) 0.17 ± 0.01 (131) 297.1 ± 40.2 (8)

73

Table 3.2. Comparison of mean C. (P.) sp. carapace length between main habitats (pool

vs riffle), sub-habitats (lateral vs main channel), seasons (spring vs fall) and sexes (male

vs female) using a repeated measures (season factor included), five factor, strip-plot (also

called a split-block) ANOVA with station (1,2,3,4) as a blocking factor [as described in

Steel and Torrie (1980)]. A weighting factor (number of crayfish collected) was used

because the number of individuals collected varied among locations. Three-way

interaction terms could not be included in the model due to missing data (see 'Crayfish

Collections') and the collection of only one sex from some locations, which resulted in

insufficient degrees of freedom. Thus, F-tests for all two-way interaction terms are

approximate (but the best that can be done) because denominators for those tests

consisted of the mean square error (MSE) instead of the more appropriate 3-way

interaction terms, e.g., Station×Sub-habitat×Season. Other F-tests were carried out as

described in Steel and Torrie (1980). C. (P.) sp. were collected from Valley Creek in

2003.

Source d.f. MS F P

Station 3 36.79 0.94 0.525

Main habitat 1 8.50 1.01 0.389

Station×Main habitat 3 8.40 0.16 0.919

Sub-habitat 1 1559.06 24.97 0.015

Station×Sub-habitat 3 62.45 1.23 0.326

Main habitat×Sub-habitat 1 184.28 3.64 0.071

Season 1 17.87 0.25 0.651

Station×Season 3 71.43 1.40 0.272

Main habitat×Season 1 0.03 0.00 0.979

Sub-habitat×Season 1 1132.91 22.27 <0.001

Sex 1 174.31 4.03 0.138

Station×Sex 3 43.29 0.85 0.483

Sub-habitat×Sex 1 11.62 0.23 0.639

Main habitat×Sex 1 206.17 4.04 0.059

Season×Sex 1 328.32 6.44 0.020

Error 19 51.09

74

Table 3.3. Comparison of C. (P.) sp. density between main habitats (pool vs riffle),

sub-habitats (lateral vs main channel), and seasons (spring vs fall) using a repeated

measures (season factor included), four factor, strip-plot (also called a split-block)

ANOVA with station (1,2,3,4) as a blocking factor [as described in Steel and Torrie

(1980)]. Station×Main habitat×Season and Station×Sub-habitat×Season interaction

terms could not be included in the model due to missing data (see 'Crayfish

Collections'), which resulted in insufficient degrees of freedom. Thus, F-tests for

Sub-habitat×Season and Main habitat×Season interaction terms are approximate (but

the best that can be done) because denominators for those tests consisted of the mean

square error (MSE) instead of the more appropriate 3-way interaction terms, e.g.,

Station×Sub-habitat×Season. Other F-tests were carried out as described in Steel and

Torrie (1980). C. (P.) sp. were collected from Valley Creek in 2003.

Source d.f. MS F P

Station 3 0.002 0.19 0.912

Main habitat 1 0.027 0.96 0.399

Station×Main habitat 3 0.028 1.39 0.388

Sub-habitat 1 0.349 486.82 <0.001

Station×Sub-habitat 3 0.001 0.03 0.990

Main habitat×Sub-habitat 1 0.022 1.05 0.380

Station×Main habitat×Sub-habitat 3 0.021 2.06 0.193

Season 1 0.007 0.65 0.479

Station×Season 3 0.011 1.09 0.415

Main habitat×Season 1 0.000 0.04 0.849

Sub-habitat×Season 1 0.003 0.31 0.595

Error 7 0.010

75

Figure 3.1. Map of the eastern United States from Pennsylvania to South Carolina with an enlargement of the study area. Valley Creek

sampling stations are numbered 1-4. Previous northern (tip of the down arrow) and southern (tip of the up arrow) limits of the C.

acuminatus complex are included on the map. VFNHP = Valley Forge National Historical Park, R = river, Cr = Creek.

StreamsSampling StationsVFNHP boundary

Valley Cr

Little Valley Cr

Crabby Cr

1

2

3

4 Schuylkill R

0 1 2 3 Kilometers

76

Figure 3.2. Length-frequency distribution of C. (P.) sp. collected from Valley Creek in 2003. Data are broken down by sex in the spring

(male n = 200, female n = 145; top left panel) and fall (male n = 127, female n = 126; bottom left panel) and by sub-habitat in the spring

[lateral n = 196, main channel (main) n = 57; top right panel] and fall (lateral n = 219, main channel n = 34; bottom right panel). Some

specimens were omitted from the top right histogram because sub-habitat data were not available for 95 individuals collected in the spring.

0

10

20

30

40

Male

Female

0

10

20

30

40

9 14 19 24 29 34 39

Spring

Fall

Nu

mb

er c

oll

ecte

d

0

10

20

30

40

50

Lateral

Main

0

10

20

30

40

50

9 14 19 24 29 34 39

Spring

Fall

Carapace length (mm)

77

Figure 3.3. Relationship between the % of the sampling area where cobble was either the

dominant or co-dominant substrate type (% cobble) and C. (P.) sp. density (no./m2) in main-

channel areas of pools. Samples were collected from Valley Creek in the spring and fall of 2003.

0

0.04

0.08

0.12

0 25 50 75 100

% Cobble

Den

sity

(n

o./

m2)

78

Figure 3.4. Relationship between depth (upper left), current velocity (upper right), substrate characteristics and C. (P.) sp. density (no./m2) in

lateral (♦) and main-channel (O) areas of pools. Substrate characteristics were calculated as the percent of the sampling area where sand (% sand,

lower left) or silt (% silt, lower right) was the dominant or co-dominant substrate type. Samples were collected from Valley Creek in the spring

and fall of 2003.

0

0.2

0.4

0.6

0 25 50 75 100

% silt

0

0.2

0.4

0.6

0 25 50 75 100

% sand

0

0.2

0.4

0.6

-0.1 0 0.1 0.2 0.3 0.4

Current velocity (m/s)

0

0.2

0.4

0.6

0 0.2 0.4 0.6 0.8

Depth (m)

Den

sity

(n

o./

m2)

79

Figure 3.5. Relationship between current velocity and C. (P.) sp. density (no./m2) in lateral (♦)

and main-channel (O) areas of riffles. Samples were collected from Valley Creek in the spring

and fall of 2003.

0

0.2

0.4

0 0.3 0.6 0.9 1.2

Current velocity (m/s)

Den

sity

(n

o./

m2)

80

Chapter 4

Crayfish Fauna of Southeastern Pennsylvania: Distributions, Ecology, and Changes over

the Last Century

Modified from:

Lieb, D.A., R.W. Bouchard, and R.F. Carline. 2011. Crayfish fauna of southeastern



Abstract

I describe the current distributions and relative abundances of southeastern

Pennsylvania‘s crayfish; changes in the region‘s crayfish fauna over the last century; and, where

pertinent, the relationship of the current fauna to site-specific characteristics, basin-wide

attributes, and exotic crayfish. The crayfish fauna currently inhabiting the region bears little

resemblance to the historical assemblage. Whereas historical surveys yielded Orconectes limosus

and C. b. bartonii, both native species, recent collections produced eight species including five

exotics. Many areas occupied by exotic Orconectes no longer support O. limosus. Cambarus b.

bartonii was found in a number of invaded systems, but was typically a minor component of the

crayfish community and may not be able to persist in those systems indefinitely. The distribution

of C. (P.) sp., an undescribed member of the C. acuminatus complex, was extremely limited,

with populations only found in four streams, all of which are threatened by urbanization and

81

exotic crayfish. Exotic species collections include the first published records for P. clarkii in

Pennsylvania and extend the ranges of Orconectes virilis and O. obscurus in the state by > 150

km. These results indicate the need for conservation and management initiatives aimed at

preserving the native crayfish that remain in southeastern Pennsylvania.

Introduction

Crayfish are a conspicuous and ecologically important component of aquatic

communities across the globe. In many water bodies, they account for a major portion of

macroinvertebrate biomass and production (Huryn and Wallace, 1987; Momot, 1995; Rabeni et

al., 1995; Haggerty et al., 2002; Haertel-Borer et al., 2005) and exert direct and indirect effects

on basal resources (detritus, algae, macrophytes) and other invertebrates (Hart, 1992; Creed,

1994; Lodge et al., 1994; Parkyn et al., 1997; Schofield et al., 2001; Nyström, 2002). They are

also an important food item for a number of species of fish, including some of recreational and

commercial importance (Rabeni, 1992; Roell and Orth, 1993; Dorn and Mittelbach, 1999; Tay et

al., 2007; Weinman and Lauer, 2007).

Crayfish diversity is highest in North America with over 400 species and subspecies

(Taylor, 2002; Taylor et al., 2007). Many of these species have limited distributions and are

threatened by exotic (introduced) crayfish, habitat destruction, pollution, urbanization, and other

human influences (Hamr, 1998; Wilcove et al., 2000; Lodge et al., 2000; Taylor, 2002; Taylor et

al., 2007). Recent conservation status assessments indicate that about half of the North American

crayfish fauna is imperiled and in need of protection (Master, 1990; Taylor et al., 1996; Master et

al., 2000; Taylor et al., 2007). Even species that were once widely distributed are rapidly

82

disappearing due to man-made disturbances (Hamr, 1998; Kazyak et al., 2005; Bouchard et al.,

2007; Loughman et al., 2009).

Despite their functional importance and threatened status, efforts to preserve and protect

North America‘s crayfish are hindered by a shortage of data. Taylor et al. (2007) estimated that

current distributional information is available for only 40% of the United States and Canadian

fauna. Even where adequate contemporary data are available, the absence or scarcity of historical

collections, particularly for large geographical areas (entire states), often makes it difficult to

assess long-term changes across landscapes. Without such data it is hard to accurately classify

individual species (endangered, threatened, stable) and develop conservation strategies for those

in decline (Jones et al., 2005; Taylor et al., 2007).

In Pennsylvania, although contemporary data are scarce and mostly unpublished,

historical collections dating back more than 100 years are available for large areas of the state

(Ortmann, 1906). Ortmann‘s monograph is one of the most thorough and important crayfish

studies ever conducted and one of the few large-scale surveys of its vintage from North America.

Nonetheless, given that over 100 years has passed since Ortmann‘s study, a reexamination of

Pennsylvania‘s crayfish fauna is overdue.

Historically, the flowing waters of southeastern Pennsylvania were believed to support

two native species of crayfish (O. limosus, C. b. bartonii), both of which were widely distributed

in the region (Ortmann, 1906). Unfortunately, the current status of those species is uncertain.

Exotic crayfish were absent from the region at the time of Ortmann‘s survey.

Recently, a member of the C. acuminatus complex [C. (P.) sp.] was discovered in

southeastern Pennsylvania (Lieb et al., 2007b; Lieb et al., 2008). Although initial surveys suggest

83

that C. (P.) sp. inhabits flowing waters, has an extremely limited range, and is native to the

region, a thorough analysis of its distribution in Pennsylvania is lacking.

The main objectives of this study were to: 1) describe the current distributions and

relative abundances of southeastern Pennsylvania‘s crayfish and, where pertinent, the

relationship of the current fauna to site-specific characteristics, e.g., stream width, basin-wide

attributes, e.g., physiography, and exotic crayfish; and 2) compare those results to historical data

(Ortmann, 1906 and miscellaneous unpublished museum records) to assess changes in the

region‘s crayfish fauna over the past century. I focused my efforts on surface-dwelling crayfish;

primary burrowers were not included in this survey because they are infrequent, transient

inhabitants of surface waters that typically occur in wet or moist terrestrial habitats where they

dig burrows to reach the underlying groundwater.


Contemporary Data

Study Area and Sampling Sites. — Contemporary (1968-2007) crayfish data from 60

lotic sites and an unknown water body (description too vague to pinpoint exact location) were

included in this study (Figure 4.1, Table 4.1). Sites were located in southeastern Pennsylvania in

an area roughly bordered by the Schuylkill River and tributaries to the north, the Pennsylvania

state line to the south, the city of Philadelphia to the east, and the western boundary of the

Delaware River basin to the west. Sixty sites were located in the Piedmont or Coastal Plain

physiographic provinces. Manatawny Creek, site 34 was positioned at the intersection of the

Ridge and Valley, New England, and Piedmont Provinces. Many sites were located in streams

that flow directly or nearly directly into the Delaware River (Delaware tributaries, sites 1-8 and

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10-15) or its largest tributary, the Schuylkill River (Schuylkill tributaries, sites 29-60).

Additional sites were located in the Brandywine and White Clay Creek drainages (sites 16-25),

which both empty into the Delaware River via the Christina River; Big Elk Creek (site 61),

which flows into the Chesapeake Bay via the Elk River; and the Schuylkill River (sites 26-28).

One site was located on Long Hook Creek (site 9), which flows out of the lower, marshy portion

of a Delaware River tributary (Darby Creek) and historically entered the Delaware River. The

northern part of the study area (the north) includes the headwaters of Brandywine Creek (sites

19-20) and the Schuylkill River and tributaries; the southern part of the study area (the south)

includes the lower Brandywine drainage (sites 16-18 and 21-22), Delaware tributaries, Long

Hook Creek, Big Elk Creek, and the White Clay drainage (sites 23-25).

Land use change is occurring at a rapid pace throughout much of the study area. As such,

many formerly rural areas are quickly becoming urbanized (Kemp and Spotila, 1997; Interlandi

and Crockett, 2003; Reif, 2004; Steffy and Kilham, 2006).

Thirty-two sites on 27 streams were thoroughly surveyed for crayfish (comprehensive

sites; Table 4.1). The remaining 29 sites located on 25 streams and one unknown water body

were sampled for other purposes, e.g., fish surveys, not specifically for crayfish (incidental sites;

Table 4.1). Comprehensive sites were georeferenced using a handheld GPS unit (model GPS 12

XL, Garmin International). The latitudes and longitudes of the incidental sites were either

provided by others or were estimated with a computer program (Terrain Navigator Pro) that uses

electronic United States Geological Survey (USGS) quadrangle maps.

Crayfish Collections. — Each comprehensive site was surveyed during daylight hours

when water clarity was high and the stream bottom was clearly visible. The lower reaches of

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Valley Creek (lower Valley Creek, sites 50-53) were sampled twice (spring and fall 2003); other

comprehensive sites were sampled once (spring 2005 or 2006). Welch Run, Fawn Run, Baptism

Creek, Spout Run, and lower Valley Creek were sampled for other projects (Lieb et al., 2007a, b;

Lieb et al., 2008); the remaining comprehensive sites were sampled specifically for this study.

At each comprehensive site, multiple riffle-pool sequences and all available habitat types

were thoroughly searched. The length of stream sampled varied from approximately 40-500 m

depending on the distance between habitat types and size of the stream. Each site was sampled

for at least one person-hour per visit. Based on earlier surveys of 53 streams located across

Pennsylvania, this level of effort frequently results in the collection of large numbers of crayfish

of all sizes and life stages and appears to be an effective method for determining community

composition and compiling species lists for individual sites (Lieb et al., 2007a). Additionally, my

effort was equal to or in excess of that used in a variety of settings to detect the presence of

stream-dwelling crayfish species (Naura and Robinson, 1998; Light, 2003; Gil-Sánchez and

Alba-Tercedor, 2006). Species were assumed to be reproducing (established) if reproductive

females (those with attached eggs or young) were found or ≥ 9 individuals, both sexes, and a

range of sizes were collected.

Most comprehensive sites were sampled with dip nets and kick seines. Dip net samples

were collected by sweeping the net through root masses, aquatic vegetation, and leaf deposits

and by turning over rocks and chasing crayfish into the net. Kick seine samples were collected

by stretching a 2.8 2.0 m bag seine with 5-mm mesh across the stream channel and disturbing

the substrate (kicking, overturning rocks) upstream of the seine. Dislodged crayfish were swept

into the seine by the current. Crayfish inhabiting slow-current habitats (pools and nearshore areas

of riffles) were usually collected with dip nets, whereas those in fast-current habitats (main

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channels of riffles) were mostly collected with kick seines. A few comprehensive sites (sites 50-

53) were sampled with electrofishing gear. The number of crayfish collected from sites 50-53

was greater than from the other sites because electrofishing gear tended to be more efficient than

dip nets and kick seines in terms of the number of specimens collected per person-hour [see Lieb

et al. (2008)] and sites 50-53 were sampled twice, whereas the other comprehensive sites were

only sampled once.

At the incidental sites, most collections contained < 10 individuals (see Table 4.1) and it

is unlikely that all habitat types were sampled or that species lists are complete. As a result, the

Crayfish Associations and Community Composition sections of this paper do not include data

from most incidental sites. The only exception was lower Manatawny Creek (sites 35-38) which

was included in the Community Composition section because collections where large (69

individuals) and the assemblage found there was not collected elsewhere during this study.

It was impossible to determine whether species were reproducing at most incidental sites

because collections included few specimens and no reproductive females. The only exception

was lower Manatawny Creek, where enough O. rusticus were collected (n = 60) to assume the

presence of a reproducing population.

Incidental collections were gathered using a variety of methods. Specimens from Crum

Creek (site 1), Little Valley Creek, and East Branch (EB) Brandywine Creek were collected with

Lium samplers (Lium, 1974) by the USGS during benthic invertebrate sampling and those from

Manatawny Creek (site 38) were collected with seines during fisheries studies carried out by the

Academy of Natural Sciences of Philadelphia (ANSP). Specimens from Dismal Run, Webb

Creek, and the Schuylkill River (site 26) were also collected by ANSP personnel but their

purpose and method of collection is unknown. Similarly, site 25 in the White Clay Creek

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drainage was sampled for unknown reasons using unknown methods. The P. clarkii attributed to

Sandy Run was found dead on a roadway that runs parallel to the creek, but was included in this

study because the species is known to exhibit overland dispersal and was likely an emigrant from

Sandy Run or another nearby water body (Bouchard et al., 2007). The remaining incidental sites

were sampled with electrofishing gear during fisheries studies conducted by ANSP. Most

incidental sites were sampled on one occasion (summer or fall) between 1996 and 2007 (Table

4.1).

After collection, crayfish were identified to species and reproductive females were noted.

The carapace length (CL) of specimens collected from comprehensive sites was determined.

Representative specimens of C. (P.) sp. were deposited at the North Carolina State Museum of

Natural Sciences (NCSM), Raleigh, North Carolina (NCSM 24749-24753, 26548-26553) or

ANSP, Philadelphia, Pennsylvania (not yet cataloged, A. Kirsch, personal communication).

Voucher specimens of O. virilis, O. limosus, O. obscurus, O. rusticus, C. b. bartonii, and P.

clarkii were deposited at ANSP (ANSP 14573, 18349, 18398, 18413, 18419, 18421-26, 18437,

18443-45, 19345-46, 19349-50, and 19352 or not yet cataloged, A. Kirsch, personal

communication). The Procambarus acutus collected from site 25 is housed at the United States

National Museum, Smithsonian Institution (USNM), Washington D.C. (USNM 129955).

Historical Data

Historical crayfish data from the study area and nearby areas were available from

Ortmann (1906), ANSP, and USNM. Ortmann (1906), which includes numerous collections

from southeastern Pennsylvania and a map (Plate XLIII) that shows the original distributions of

Pennsylvania‘s crayfish (including C. b. bartonii and O. limosus), was a particularly useful

88

resource. At most of Ortmann‘s sites, it appears that efforts were made to collect all the crayfish

species that were present. Collections were generally made by hand or with a dip net. Additional

collection information is provided in Ortmann (1906). For the remaining historical sites (USNM

and ANSP records), sampling methods were not recorded.


Taxonomy of C. (P.) sp. in Pennsylvania

Although it will not be possible to attach a species name to my C. (P.) sp. collections

until a thorough taxonomic analysis of the northern members of the C. acuminatus complex is

completed (Lieb et al., 2008), I doubt that they include multiple species because of the proximity

of my collection sites (Figure 4.2) and morphological similarity of my specimens. If later

taxonomic studies were to show that multiple species of Puncticambarus occur within the study

area, it will be possible to attach the correct species name to my collections because I have

deposited representative specimens of C. (P.) sp. from all the streams where it was collected in

museums.

Overview of Crayfish Collections

A total of 1416 crayfish belonging to eight species was collected during contemporary

surveys (Table 4.1, 4.2). Of these, 1165 were collected from 37 sites (25 streams) in the north;

the remaining 251 were collected from 24 sites (20 streams) in the south (Figure 4.1, Table 4.1,

4.2). More crayfish were collected from lower Valley Creek (613 individuals) than from the

other northern sites (552 individuals) because sampling efforts were greater in lower Valley

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Creek than elsewhere. Due to this potential bias, the abundance summaries (number collected,

relative abundance) provided in the remainder of this section do not include data from lower

Valley Creek (see Table 4.2 for further explanation).

Contemporary surveys yielded five exotic crayfish including P. acutus, which is native to

extreme southeastern Pennsylvania (Coastal Plain and nearby areas of the Piedmont) but not to

most of the study area (Bouchard et al., 2007); O. obscurus, which is native to western but not

eastern Pennsylvania (Ortmann, 1906; Bouchard et al., 2007); and O. virilis, O. rusticus, and P.

clarkii, which are not naturally found anywhere in the state (Taylor et al., 1996, 2007) (Table

4.1, 4.2). The P. clarkii data provided herein are of particular significance because they are the

first published records for Pennsylvania (Ortmann, 1906; Hobbs, 1972, 1989; and Taylor et al.,

2007) and increase the number of known crayfish species in the state. Records of O. rusticus, O.

virilis, and O. obscurus are the first that have been published for southeastern Pennsylvania.

Contemporary collections also included C. b. bartonii and O. limosus, which historically

occurred throughout the study area (Ortmann, 1906), and the recently discovered C. (P.) sp.

(Table 4.1, 4.2). Collectively, recent efforts have added five species (four exotics and one native)

to the known crayfish fauna of southeastern Pennsylvania. The region‘s crayfish fauna is now

vastly different than that encountered by Ortmann (1906). Such differences tended to be much

more pronounced to the north, where exotic crayfish (mostly Orconectes) were common, than to

the south (Figure 4.2, 4.3, Table 4.1, 4.2).

Across the study area, C. b. bartonii was the most frequently collected crayfish (269

individuals, 33% of the catch), followed by O. rusticus (204 individuals, 25% of the catch) and

O. limosus (144 individuals, 18% of the catch); other crayfish accounted for < 10% of the catch

(Table 4.1, 4.2). In the north, O. rusticus was the most commonly collected crayfish, followed by

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C. b. bartonii and O. obscurus; other crayfish were uncommon (Table 4.2). The scarcity of O.

limosus in the north, an area that it once fully occupied, was especially noticeable. In contrast, in

the south, O. limosus was the most frequently collected crayfish, followed by C. b. bartonii and

C. (P.) sp.; other crayfish were rarely collected (Table 4.2). The rarity of O. rusticus, O.

obscurus, and O. virilis in the south was particularly evident given their comparative abundance

to the north.

Contemporary Distributions and Range Changes

Cambarus b. bartonii. — During this study, C. b. bartonii was collected from 31 sites

(29 streams) (Figure 4.3, Table 4.1, 4.2). These sites were in the Coastal Plain (n = 1), Piedmont

(n = 29), and at the intersection of the Ridge and Valley, New England, and Piedmont (n = 1).

Cambarus b. bartonii was found in 21 of the 24 small to midsized streams that were

comprehensively surveyed and was common throughout all parts of the study area except the

Coastal Plain. These results agree with Ortmann (1906) who concluded that, although C. b.

bartonii was generally absent from large rivers in Pennsylvania, ‗‗conditions seem to be

favorable for this species everywhere, possibly with the exception of the Coastal Plain‘‘ and

suggests that the range of C. b. bartonii in southeastern Pennsylvania has remained relatively

stable over the past century.

Cambarus b. bartonii has been able to persist over the long-term in a number of streams

in the study area. More specifically, C. b. bartonii was collected from Cobbs and Darby creeks in

the early 1900s (ANSP 4783-84 and 5023), from Ridley and White Clay creeks in the 1950s

(ANSP 6149, 6215-18, and 6224-25), and from all four of those creeks in 2006 (Figure 4.3,

Table 4.1). However, exotic crayfish are currently not found in any of those waterways and it

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remains to be seen whether C. b. bartonii can coexist with exotic crayfish over the long-term in

southeastern Pennsylvania.

Cambarus (P.) sp. — During this study, C. (P.) sp. was collected from 13 sites (eight

streams) (Figure 4.2, Table 4.1, 4.2). These sites were in the Coastal Plain (n = 1) and Piedmont

(n = 12) and were located within a relatively small area (~ 220 km2) extending from Pickering

Creek southeast to the lower reaches of Darby Creek within ~ 30 km of Philadelphia. Most C.

(P.) sp. sites were located to the north in the Schuylkill River and its tributaries, which is mainly

due to the large number of collections from the Valley Creek basin. Cambarus (P.) sp. was also

collected from tributaries of the Delaware River, but was not collected from the Brandywine and

White Clay Creek drainages. Most of the C. (P.) sp. collected during this study (n = 666) were

found in the Pickering, Valley, Darby, and Crum Creek drainages. The remaining individuals

were collected from Welch Run and the Schuylkill River.

A reproducing population of C. (P.) sp. occurs in Valley Creek (Lieb et al., 2008, Figure

4.2, Table 4.1). Surveys done specifically for this study uncovered additional reproducing

populations of C. (P.) sp. in Pickering, Crum, and Darby creeks (Figure 4.2, Table 4.1). These

findings are not particularly surprising given that the headwaters of Valley Creek are < 2 km

from those of Darby, Pickering, and Crum creeks and the headwaters of Darby and Crum creeks

are < 2 km from each other (Figure 4.2). Dams are located downstream of the Crum, Darby, and

Pickering Creek populations and may be preventing them from being colonized by exotic

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crayfish, which occur in a number of nearby waterways (Lieb and Bhattarai, 2009 and Figure

4.2).

A thorough search of sites on the Schuylkill River and Welch Run resulted in the

collection of only two C. (P.) sp. (Table 4.1). This suggests that reproducing populations of the

species do not occur in those waterways. Instead, individuals collected at those sites were

probably emigrants from nearby Valley Creek or Pickering Creek (Figure 4.2).

Orconectes limosus. — During this study, O. limosus was collected from 17 sites (16

streams) (Figure 4.3, Table 4.1, 4.2). Sites were in the Coastal Plain (n = 4), Piedmont (n = 12),

and at the intersection of the Ridge and Valley, New England, and Piedmont (n = 1). Most O.

limosus sites were located in the south, where exotic crayfish were rare. Northern occurrences of

O. limosus were limited to three sites, all of which were located on Schuylkill tributaries and

were devoid of exotic Orconectes. Reproducing populations of O. limosus were found in eight

streams, seven of which are in the south. The apparent absence of O. limosus from much of the

north (Figure 4.3, Table 4.1, 4.2), a region it once fully occupied [see Ortmann (1906)], suggests

a substantial range reduction over the past century, although it is possible that some

undiscovered populations remain to the north or that population sizes have declined substantially

making existing populations extremely difficult to detect.

In the early 1900s, O. limosus was collected from a ~ 90 km stretch of the Schuylkill

River (Philadelphia upstream to Reading) where it was sometimes ‗‗exceedingly abundant‘‘

(Ortmann, 1906). In the 1950s, O. limosus was again collected from multiple locations along that

reach (ANSP 5674 and 6229); however, recent crayfish surveys in that section yielded large

numbers of exotic O. rusticus, which was not previously collected from the Schuylkill River, but

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no O. limosus (Table 4.1). Similarly, O. limosus was collected from an upstream reach of EB

Perkiomen Creek in the 1930s (USNM 131923), but contemporary collections produced only O.

rusticus (Table 4.1). Although contemporary collections from EB Perkiomen Creek were not

comprehensive, O. limosus and O. rusticus have never been found together at the same site in the

study area (Table 4.1), potentially due to the elimination of resident O. limosus by exotic O.

rusticus. In Pennsylvania, O. rusticus has been collected from 59 sites, but with O. limosus at

only one of them, a recently invaded site in the northeastern part of the state (Bouchard et al.,

2007; Lieb et al., 2007a; D.A. Lieb, PSU and R.W. Bouchard, ANSP, unpublished data).

In other parts of the Perkiomen Creek drainage, historical collections produced only O.

limosus, while those completed more recently yielded only O. rusticus (Figure 4.1, 4.3, 4.4,

Table 4.1). Direct comparisons are not possible because historical collections (1916-1943) were

from headwater reaches (Perkiomen Creek at Pennsburg, ANSP 5307; Hosensack Creek, ANSP

5332; unnamed tributary of Pleasant Spring Creek, USNM 131914), whereas recent efforts have

been from downstream areas (Perkiomen and Swamp Creeks). Nonetheless, since O. limosus

was historically more common in the larger, downstream reaches of Pennsylvania‘s river

networks than in smaller, upstream tributaries (Ortmann, 1906); it seems unlikely that O. limosus

would have been found in the headwaters of Perkiomen Creek but not in downstream areas.

Thus, I suspect that O. limosus was once found throughout much of the Perkiomen drainage but

no longer occurs in downstream areas. Although the headwaters of Perkiomen Creek have not

been sampled in > 60 years, O. limosus may have been afforded protection from O. rusticus

invasions by the dam on Green Lane Reservoir (Figure 4.3, 4.4).

In the south, O. limosus was relatively common and the species seems to have retained

much of its original range (Ortmann, 1906; Figure 4.3, Table 4.1, 4.2). For example, resampling

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efforts in Marcus Hook and Brandywine creeks found that populations of O. limosus were still

present in those waterways 100 years later (Ortmann, 1906; Table 4.1). Recent collections from

the headwaters of Brandywine Creek included large numbers of exotic O. virilis and O. obscurus

but no O. limosus (Table 4.1), suggesting that the continued existence of downstream

populations of O. limosus in Brandywine Creek is not assured.

Overall, I suspect that exotic crayfish (particularly O. obscurus, O. rusticus, and O.

virilis) are a major reason for the absence of O. limosus from much of the north including a

substantial section of the Schuylkill River, a number of Schuylkill tributaries, and some

headwater reaches in the Brandywine basin. In contrast, the scarcity of exotic crayfish to the

south probably explains the persistence of O. limosus in that region. It is also possible that

environmental and/or biological conditions have changed to the north but not the south

contributing to the absence of O. limosus from the north, although such changes were not

apparent during field collections.

Within the study area, reproducing populations of O. limosus were found in running

water systems that ranged from small streams (EB White Clay Creek: generally < 10 m wide) to

large rivers (Brandywine Creek: generally > 30 m wide). This finding is in agreement with

Ortmann (1906) who found that, although O. limosus preferred larger waterways, the species

occurred throughout drainage networks (headwater streams to large rivers).

Orconectes obscurus. — During this study, O. obscurus was collected from eight sites

(five streams) in the Piedmont (Figure 4.4, Table 4.1, 4.2). All were in the north, but were widely

scattered, suggesting multiple introductions. One site was located in the headwaters of

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Brandywine Creek, where the species is reproducing; the remaining sites were located in

Schuylkill tributaries, two of which also support reproducing populations.

The O. obscurus records herein extend the known range of the species in Pennsylvania

substantially eastward. More specifically, to the best of my knowledge, the previous eastern-

most, published O. obscurus localities for Pennsylvania are located > 200 km to the west of

Wissahickon Creek in the north central and south central parts of the state [upper Genesee River

drainage, Potter County and Willis Creek, Bedford County (Ortmann, 1906)].

In the study area, O. obscurus was collected from small to midsized streams (~ 5-30 m

wide). Orconectes obscurus was not collected from any of the large river sites (Perkiomen

Creek, Brandywine Creek, Schuylkill River; Table 4.1), even though in its native range (western

Pennsylvania) it generally prefers such sites (Ortmann, 1906). The presence of O. rusticus at

most of the large river sites may be responsible for the absence of O. obscurus at those locations,

as has been found in parts of Ohio and New York (Thoma and Jezerinac, 2000; Kuhlmann and

Hazelton, 2007).

Orconectes rusticus. — During this study, O. rusticus was collected from 12 sites

(seven streams) in the Piedmont (Figure 4.4, Table 4.1, 4.2). All were in the north and were

located either in the Schuylkill River or its tributaries. Reproducing populations of the species

were found in five streams. Notably, O. rusticus was the only crayfish collected from the lower

Perkiomen Creek drainage (sites 39-42) and occurs far upstream in the headwaters of at least one

tributary in that drainage (EB Perkiomen Creek). Similarly, aside from the collection of a single

C. (P.) sp., which was probably an emigrant from elsewhere, and a single P. clarkii, O. rusticus

was the only crayfish collected from the Schuylkill River. Because exotic O. rusticus tend to

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eliminate other crayfish from invaded sites through time (St. John, 1991; Taylor and Redmer,

1996; Wilson et al., 2004; Kuhlmann and Hazelton, 2007), it seems likely that, within the study

area, O. rusticus introductions occurred first in the Schuylkill River or in the lower Perkiomen

drainage. It also appears that environmental conditions, e.g., temperature, nutrient

concentrations, at those sites are particularly favorable for O. rusticus, allowing the species to

thrive there. More specifically, the Schuylkill River and lower Perkiomen Creek are relatively

large (generally > 50 m wide), warm, enriched [Jaworski and Hetling, 1996; Jaworski et al.,

1997; Pennsylvania Department of Environmental Protection (PADEP), 2003], and negatively

impacted by a variety of anthropogenic stressors (Weisberg and Burton, 1993; Fairchild et al.,

1998; Steyermark et al., 1999; Interlandi and Crockett, 2003; PADEP, 2003), all of which tend to

favor O. rusticus relative to resident species (Momot, 1984; Jezerinac, 1986; Butler, 1988;

Momot et al., 1988; Mundahl and Benton, 1990; St. John, 1991; Jezerinac et al., 1995; Thoma

and Jezerinac, 2000).

Within the study area, O. rusticus sites ranged from large, warm rivers at the base of

drainage networks (Perkiomen Creek, Schuylkill River) to small, cooler streams near the

headwaters (EB Perkiomen Creek) (Figure 4.4, Table 4.1) and included visibly polluted

waterways in highly urbanized watersheds (Trout Creek), as well as higher quality streams

draining mostly forested and agricultural lands (French and Manatawny creeks; Thomson et al.,

2005; J.K. Jackson, Stroud Water Research Center, unpublished data). Collectively, these data

indicate that O. rusticus is a highly-adaptable, tolerant species that has been able to colonize a

wide variety of running water systems in southeastern Pennsylvania, as has been found

elsewhere (St. John, 1982, 1991; Page, 1985; Hobbs and Jass, 1988; Hobbs et al., 1989; Thoma

and Jezerinac, 2000; Taylor and Schuster, 2004; Guiaşu, 2007). Because of this, the spread of O.

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rusticus into new areas may be more limited by dispersal (both natural and human-assisted) than

by the availability of suitable environmental conditions. It is possible; however, that exotic O.

rusticus may be less successful in cool, nutrient-poor, headwater streams than in warmer, more

productive, downstream reaches as predicted by Momot (1984) and as appears to be the case in

Ohio (Mundahl and Benton, 1990; Thoma and Jezerinac, 2000). If so, in southeastern

Pennsylvania and elsewhere, some native species may be able to persist in the headwaters of

invaded systems, where O. rusticus is absent or less abundant. This is particularly likely for C. b.

bartonii, which naturally occurs in headwater streams throughout the eastern United States

(Ortmann, 1906; Crocker, 1957, 1979; Francois, 1959; Meredith and Schwartz, 1960; Jezerinac

et al., 1995; Seiler and Turner, 2004). Unfortunately, for those native species that prefer larger,

downstream reaches, e.g., O. limosus (Ortmann, 1906), direct competition with O. rusticus may

be unavoidable.

Orconectes virilis. — During this study, O. virilis was collected from three sites in the

Piedmont and one site in the Coastal Plain and was more common in the north than south (Figure

4.4, Table 4.1, 4.2). Orconectes virilis collections were widely scattered, suggesting multiple

introductions and included a site in the headwaters of Brandywine Creek, where the species is

reproducing, and sites on Schuylkill and Delaware tributaries.

The localities herein extend the known range of O. virilis in Pennsylvania substantially

eastward. More specifically, to the best of my knowledge, the previous easternmost published O.

virilis record for Pennsylvania is located > 150 km to the west of Hermesprota Creek in the south

central part of the state [Marsh Creek, Adams County; USNM record listed in Hobbs (1989)].

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Within the study area, O. virilis was collected from small to midsized streams (~ 5-30 m

wide) that varied with regards to temperature and upstream land use. More specifically, Trout

and Hermesprota creeks are warm-water fisheries, while French and West Branch (WB)

Brandywine creeks support cold-water fishes (trout) for much of the year. Similarly, Trout and

Hermesprota creeks are located in highly urbanized areas, whereas French and WB Brandywine

creeks are located in more rural settings with mixed land use. Overall, O. virilis was collected

from a variety of stream types in southeastern Pennsylvania, as has been found in other parts of

its introduced range (Schwartz et al., 1963; Bouchard, 1976; Jezerinac et al., 1995; McGregor,

1999).

Procambarus acutus. — Procambarus acutus was collected from two sites in the

Piedmont during this study: a Schuylkill tributary in the north and a site in the White Clay

drainage in the south (Figure 4.4, Table 4.1, 4.2). The distance between sites suggests separate

introductions. A private aquaculture facility, which sells P. acutus and is located ~ 20 km west of

the northern site, may be responsible for the presence of the species in the area.

Although P. acutus is expanding its range in Pennsylvania due to introductions, native P.

acutus have not been collected from Pennsylvania since the early 1900s and few thorough

surveys in its native range in southeastern Pennsylvania have been conducted (Bouchard et al.,

2007; Figure 4.1, Table 4.1). For this reason, additional surveys in its native range are needed.

Procambarus clarkii. — Procambarus clarkii was collected from three sites in the

Piedmont and one site in the Coastal Plain during this study (Figure 4.4, Table 4.1, 4.2). These

collections were widely scattered suggesting multiple introductions and included sites to the

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north in the Schuylkill River and its tributaries, one of which supports a reproducing population,

and a site to the south in Long Hook Creek.

Procambarus clarkii sites varied substantially in size, gradient, and temperature. More

specifically, sites on Sandy Run and Wissahickon Creek were generally < 15 m wide, whereas

the Schuylkill River site was > 50 m across. Similarly, the Schuylkill River is a warm-water

fishery, while Wissahickon Creek supports trout for much of the year. Long Hook Creek is a

low-gradient, marshy stream, whereas Wissahickon Creek is a higher-gradient, rocky stream.

Procambarus clarkii sites tended to be similar with regards to upstream land use (all in urban

areas) and nutrient status (most enriched) (Jaworski and Hetling, 1996; Jaworski et al., 1997;

Butler et al., 2001; Philadelphia Water Department, 2004; PADEP, 2006). These findings are not

unexpected given that, although P. clarkii has been widely introduced to a variety of habitats

(swampy lowlands and ponds to trout streams; Hobbs et al., 1989; Dehus et al., 1999; Gherardi et

al., 1999; Thoma and Jezerinac, 2000; Huner, 2002), some authors have noted their apparent

preference for developed (urbanized) areas and enriched waters in parts of their introduced range

(Diéguez-Uribeondo et al., 1997; Gil-Sánchez and Alba- Tercedor, 2002; Riley et al., 2005).

The discovery of P. clarkii in southeastern Pennsylvania is not particularly surprising

given the presence of exotic populations in Maryland, New York, and Ohio (Thoma and

Jezerinac, 2000; Daniels, 2004; Kazyak et al., 2005; Kilian et al., 2009) and cultured populations

in western Pennsylvania. Although particular dispersal mechanisms are not known, P. clarkii

probably initially reached southeastern Pennsylvania via human assistance (release or escape of

laboratory specimens, aquarium pets, fishing bait, commercially cultured animals), as has

occurred elsewhere (Hobbs, 1989; Campos and Rodriguez-Almaraz, 1992; Bouchard et al.,

100

2007; Larson and Olden, 2008; Kilian et al., 2009). Upon arrival, the presence of urbanized,

enriched systems likely favored its establishment in the area.

Crayfish Associations

At most sites, either one or two species of crayfish were collected (Table 4.1). Common

species pairs were C. b. bartonii and O. limosus and C. b. bartonii and C. (P.) sp. Cambarus b.

bartonii was collected from all streams (and five of seven sites) where reproducing populations

of C. (P.) sp. were found and six of eight streams (sites) where reproducing populations of O.

limosus were found. Cambarus b. bartonii has also been collected with the C. acuminatus

complex in parts of Virginia (Hobbs et al., 1967).

Cambarus b. bartonii was collected with exotic crayfish at a number of sites in the north

including six of seven comprehensive sites inhabited by P. acutus, P. clarkii, O. virilis, and O.

obscurus and two of six comprehensive sites inhabited by O. rusticus (Figure 4.3, 4.4, Table

4.1). The association of C. b. bartonii with O. obscurus was not surprising given they co-occur

elsewhere and when sympatric appear to avoid direct competition by selecting different habitats

(Jezerinac et al., 1995; Hamr, 1998; Kuhlmann and Hazelton, 2007; D.A. Lieb, PSU and R.W.

Bouchard, ANSP, unpublished data). Cambarus b. bartonii is also found with exotic crayfish in

other parts of Pennsylvania (Bouchard et al., 2007; Lieb et al., 2007a; R.W. Bouchard, ANSP

and D.A. Lieb, PSU, unpublished data). These results suggest that the continued prevalence of C.

b. bartonii in the north is probably due to its ability to coexist with exotic crayfish.

Cambarus b. bartonii was never found exclusively with O. rusticus, but was collected

with O. rusticus and O. virilis (Table 4.1). Although it is unclear why C. b. bartonii and O.

rusticus were only found together with other species, this tendency was not restricted to the study

101

area. Elsewhere in Pennsylvania, C. b. bartonii and O. rusticus were found together in eight

streams but exclusively in only two of them (Lieb et al., 2007a; R.W. Bouchard, ANSP and D.A.

Lieb, PSU, unpublished data). Because exotic O. rusticus typically eliminate O. virilis (Berrill,

1978; Capelli, 1982; Taylor and Redmer, 1996; Wilson et al., 2004), they are probably not

permanent associates in southeastern Pennsylvania. Instead, the O. virilis collected were

probably remnants of larger populations, emigrants from elsewhere in their respective

watersheds, or recent introductions. Because C. b. bartonii can sometimes persist with exotic O.

rusticus (Hamr, 2002; D.A. Lieb, PSU and R.W. Bouchard, ANSP, unpublished data), their

association may be more permanent.

Cambarus (P.) sp. was collected with O. rusticus in the Schuylkill River but was absent

from other invaded sites (Figure 4.2, 4.4, Table 4.1). Because the single C. (P.) sp. collected

from the Schuylkill River was likely an emigrant from elsewhere, C. (P.) sp. is probably only an

occasional, transient associate of O. rusticus in that waterway. Crayfish surveys conducted in the

summer of 2008 by the National Park Service (NPS) indicate that O. rusticus has recently

invaded lower Valley Creek and currently coexists with C. (P.) sp. (Kristina Heister, NPS,

personal communication), although C. (P.) sp. appears to be in decline and may eventually

disappear from the system.

Orconectes limosus was only collected with exotic crayfish at one site and was never

found with exotic Orconectes (Figure 4.3, Table 4.1). The apparent inability of O. limosus to

coexist with exotic congeners probably contributed to its absence from much of the north.

102

Community Composition

Uninvaded sites supported one species of crayfish or if multiple species were present O.

limosus or C. (P.) sp. usually accounted for a substantial portion of the collections (43-98%),

with C. b. bartonii comprising most of the remaining catch (Table 4.1). The preference of O.

limosus and C. (P.) sp. for slow-current areas probably favored their coexistence with C. b.

bartonii, which tend to select areas with faster-current (Ortmann, 1906; Lieb et al., 2008; D.A.

Lieb, PSU, personal observations). The preference of O. limosus and C. (P.) sp. for similar

habitats may have prevented their coexistence and contributed to their mostly allopatric

distribution in the study area.

Collections at most invaded sites were dominated by one species of exotic Orconectes;

other species were usually uncommon (Table 4.1). Where found, O. rusticus usually comprised

75% of the catch. In the absence of O. rusticus, O. obscurus and O. virilis accounted for 63-

100% of the catch, whereas those species usually constituted ≤ 25% of the catch in the presence

of O. rusticus. The dominance of O. rusticus will likely increase in the future as populations of

O. obscurus and O. virilis are further reduced or eliminated.

Cambarus b. bartonii was uncommon at invaded sites (relative abundance ≤ 20%) but

was frequently an important member of the crayfish community in the presence of native

crayfish (relative abundance often > 20% and sometimes 50%) (Table 4.1). These data along

with observations from Maryland and other parts of Pennsylvania, where C. b. bartonii is not

always able to coexist with exotic crayfish (Schwartz et al., 1963; D.A. Lieb, PSU and R.W.

Bouchard, ANSP, unpublished data), suggest that, although the range of C. b. bartonii in

southeastern Pennsylvania has remained relatively stable over the past century, its continued

persistence in the region is not assured and will depend on its ability to coexist with exotic

103

crayfish over the long-term, potentially at reduced densities and as a minor component of the

crayfish community.

Concluding Remarks and Conservation Implications

The results presented herein suggest that there have been substantial changes in the

crayfish fauna of southeastern Pennsylvania over the past century. The prevalence of exotic

crayfish in the region and apparent disappearance of O. limosus from invaded areas was

particularly noticeable. Although C. b. bartonii was found in a number of invaded systems, it

was typically a minor component of the crayfish community and may not be able to persist in

those systems over the long-term.

In addition to documenting changes, this study also provides important distributional

information for C. (P.) sp. More specifically, the data herein along with results from less-

focused, larger-scale surveys (Lieb et al., 2007a; Bouchard et al., 2007) indicate that C. (P.) sp.

has an extremely restricted distribution in Pennsylvania, with collections limited to 13 sites and

reproducing populations only known from four streams, all of which are located in a rapidly

expanding urban area in close proximity to several species of exotic crayfish (Figure 4.2, 4.4).

Based on these findings, the native crayfish fauna of southeastern Pennsylvania is clearly

in decline and conservation measures targeting the group are urgently needed. The protection of

existing populations of C. (P.) sp. and O. limosus is of particular importance and will probably

require measures aimed at preventing crayfish introductions and reducing the impacts of urban

development. The recent invasion of lower Valley Creek by O. rusticus and apparent decline in

resident C. (P.) sp. illustrate the urgency of the situation. Although C. b. bartonii is not an

immediate conservation concern in the region, existing populations (particularly those in invaded

104

systems) should be monitored periodically. Overall, I suspect that, without management

intervention, native crayfish will continue to disappear from southeastern Pennsylvania and may

eventually be lost from much of the region.

Acknowledgements

I thank Nellie Bhattarai, Hannah M. Ingram, and Jeremy Harper for their substantial

contributions. The Wild Resources Conservation Fund, Pennsylvania Department of

Conservation and Natural Resources (Project Number AG050523); the National Park Service

(Grant Agreement H4560030064); and a Pennsylvania State Wildlife Grant (number

PFBC050305.01) provided financial support. Christopher A. Urban, Matt R. Marshall, and Sarah

Nichols administered grants and provided encouragement. Marybeth Lieb, John E. Cooper, and

an anonymous reviewer provided helpful critiques of the paper and Erin Greb assisted with

figure preparation. Drew Reif, Mike Bilger, Rafael Lemaitre, and especially Richard J. Horwitz

and Paul F. Overbeck provided museum records or crayfish specimens. The Stroud Water

Research Center granted access to White Clay Creek.

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Table 4.1. Contemporary (1968-2007) crayfish collections at individual sampling sites in southeastern Pennsylvania. Sites denoted with single asterisks (*) were not specifically

surveyed for crayfishes (incidental sites). At the remaining sites, a thorough crayfish survey was conducted (comprehensive sites). Reproducing populations of Orconectes,

Procambarus, and C. (P.) sp. are denoted by double asterisks (**). Except for Long Hook Creek, which flows out of lower Darby Creek, tributaries are indented below the stream

they flow into. For streams sampled at multiple locations, upstream sites are listed first followed by downstream sites. Abbreviations used: WB = West Branch, EB = East

Branch, Cr = Creek, R = River, Lat = Latitude, Long = Longitude, Coll = Collection, Rel ab = Relative abundance, Phys = Physiographic province, CP = Coastal Plain, P =

Piedmont, Int = intersection of Ridge and Valley, New England, and Piedmont, P. = Procambarus (genus) or Puncticambarus (subgenus), O. = Orconectes, and C. = Cambarus.

BBerried female(s) collected. YFemale(s) with attached young collected.

Lat, Long Coll Rel ab

Stream Site Phys (decimal °) date Species N (%)

Delaware R - - - - - - -

Crum Cr 1* P 40.0078, -75.4653 31Oct82 C. b. bartonii 1 100

Crum Cr 2 P 39.98975, -75.43623 11May06 C. b. bartonii 17 53

- - - - - C. (P.) sp.**B

14

44

- - - - - O. limosus**B

1

3

Darby Cr 3 P 39.98899, -75.34277 11May06 C. b. bartonii 5 16

- - - - - C. (P.) sp.**B 26 84

Darby Cr 4* CP 39.93470, -75.27715 25Jul06 C. (P.) sp. 2 29

- - - - - O. limosus 5 71

Cobbs Cr 5 P 39.97462, -75.27971 11May06 C. b. bartonii 8 100

Cobbs Cr 6* CP 39.935, -75.237 09Dec99 O. limosus 1 100

Indian Cr 7* P 39.97776, -75.26163 02Jun98 C. b. bartonii 1 100

Hermesprota Cr 8* CP 39.89126, -75.26816 21Mar07 O. virilis 1 100

Long Hook Cr 9* CP 39.87570, -75.28708 28Jul05 P. clarkii 1 100

Marcus Hook Cr 10* CP 39.83111, -75.41056 24Jul06 C. b. bartonii 2 29

- - - - - O. limosus 5 71

Ridley Cr 11 P 39.95732, -75.44373 11May06 C. b. bartonii 11 34

116

- - - - - O. limosus**B

21 66

Ridley Cr 12* CP 39.86396, -75.34930 14Jul06 O. limosus 5 100

Dismal Run 13* P 39.94050, -75.42208 10Oct01 C. b. bartonii 7 100

WB Chester Cr 14 P 39.88972, -75.50741 11May06 O. limosus**B

7 100

Webb Cr 15* P 39.88778, -75.51085 1996 C. b. bartonii 1 100

- - - - 2001 O. limosus 3 100

Christina R - - - - - - -

Brandywine Cr 16 P 39.87080, -75.59408 10May06 O. limosus**B 25 100

EB Brandywine Cr 17* P 39.9264, -75.6483 16Oct84 O. limosus 1 100

Valley Cr 18 P 39.98410, -75.66499 10May06 C. b. bartonii 2 50

- - - - - O. limosus**B 2 50

Marsh Cr 19 P 40.08893, -75.72986 24May06 C. b. bartonii 6 20

- - - - - O. obscurus**

24 80

WB Brandywine Cr 20 P 40.02079, -75.84770 24May06 C. b. bartonii 1 4

- - - - - O. virilis** 25 96

Buck Run 21 P 39.93254, -75.83024 10May06 C. b. bartonii 4 36

- - - - - O. limosus**B 7 64

EB West Cr 22* P 39.89929, -75.78776 23Sep98 C. b. bartonii 1 100

White Clay Cr - - - - - - -

EB White Clay Cr 23 P 39.85888, -75.78330 12May06 C. b. bartonii 14 23

- - - - - O. limosus**B 47 77

Big Springs 24* P 39.87045, -75.82217 08Oct97 C. b. bartonii 1 100

Unknown Waterbody 25* P 39.82273, -75.82014 1968 P. acutus 1 100

Schuylkill R 26* P 40.15043, -75.52813 16Aug90 P. clarkii 1 100

Schuylkill R 27 P 40.11274, -75.47120 10May06 O. rusticus**Y 36 100

Schuylkill R 28 P 40.10878, -75.42163 09May06 C. (P.) sp. 1 10

- - - - - O. rusticus** 9 90

Abrams Cr 29* P 40.10171, -75.38222 19Oct99 O. limosus 1 100

Fawn Run 30 P 40.10846, -75.45197 31Mar05 C. b. bartonii 7 78

117

- - - - - Cambarus sp. 2 22

French Cr 31 P 40.13784, -75.55293 10May06 C. b. bartonii 4 9

- - - - - O. rusticus** 34 79

- - - - - O. virilis 5 12

Baptism Cr 32 P 40.20717, -75.76261 31Mar05 C. b. bartonii 52 100

Spout Run 33 P 40.20740, -75.76910 31Mar05 C. b. bartonii 80 91

- - - - - Cambarus sp. 8 9

Manatawny Cr 34 Inter 40.31870, -75.73337 25May06 C. b. bartonii 12 57

- - - - - O. limosus 9 43

Manatawny Cr 35* P 40.26862, -75.66433 25Aug06 O. rusticus** 27 100

Manatawny Cr 36* P 40.26240, -75.66155 16Aug05 O. rusticus** 1 100

- - - - 01Aug06 O. obscurus 2 9

- - - - - O. rusticus** 21 91

Manatawny Cr 37* P 40.25146, -75.65712 31Jul06 O. obscurus 5 50

- - - - - O. rusticus 5 50

Manatawny Cr 38* P 40.24663, -75.65649 29Aug05 O. rusticus 2 100

- - - - 13Oct06 O. obscurus 2 33

- - - - - O. rusticus 4 67

Perkiomen Cr 39 P 40.13085, -75.44541 10May06 O. rusticus**Y 8 100

Perkiomen Cr 40 P 40.12224, -75.44880 10May06 O. rusticus**B 39 100

EB Perkiomen Cr 41* P 40.4105, -75.2233 01Jul05 O. rusticus 5 100

Swamp Cr 42* P 40.27509, -75.53186 10Sep02 O. rusticus 2 100

Pickering Cr 43 P 40.10160, -75.53617 10May06 C. b. bartonii 1 6

- - - - - C. (P.) sp.** 17 94

Pine Cr 44* P 40.08811, -75.61318 17Oct01 C. (P.) sp. 1 100

Pigeon Cr 45 P 40.20276, -75.60206 25May06 C. b. bartonii 5 100

Stony Cr 46 P 40.12896, -75.34351 09May06 O. obscurus**B 5 100

Stony Run 47 P 40.17007, -75.57869 25May06 C. b. bartonii 1 17

- - - - - O. limosus**B 3 50

118

- - - - - P. acutus 2 33

Trout Cr 48 P 40.10587, -75.40745 09May06 C. b. bartonii 2 14

- - - - - O. rusticus**BY

11 79

- - - - - O. virilis 1 7

Valley Cr 49* P 40.0416, -75.5765 31Jul05 C. (P.) sp. 2 100

Valley Cr 50 P 40.08223, -75.45399 21Apr03 C. b. bartonii 3 2

- - - - - C. (P.) sp.** 121 98

- - - - 18Oct03 C. b. bartonii 2 2

- - - - - C. (P.) sp.** 85 97

- - - - - Cambarus sp. 1 1

Valley Cr 51 P 40.08845, -75.45674 22Apr03 C. (P.) sp.** 27 100

- - - - 18Oct03 C. (P.) sp.** 83 100


- - - - 18Oct03 C. b. bartonii 4 6

- - - - - C. (P.) sp.** 60 94


- - - - 19Oct03 C. (P.) sp.** 27 100

Little Valley Cr 54* P 40.0667, -75.4728 18Oct85 C. (P.) sp. 1 100

Welch Run 55 P 40.10337, -75.46904 31Mar05 C. b. bartonii 17 81

- - - - - C. (P.) sp. 1 5

- - - - - Cambarus sp. 3 14

Wissahickon Cr 56 P 40.18674, -75.25484 25May06 C. b. bartonii 1 4

- - - - - O. obscurus**Y 17 63

- - - - - P. clarkii** 9 33

Wissahickon Cr 57* P 40.07852, -75.22545 15Jul03 O. obscurus 1 100

- - - - 13Jul06 O. obscurus 1 100

Cresheim Cr 58* P 40.0604, -75.2018 04Jun98 C. b. bartonii 1 100

Rose Valley Cr 59* P 40.16030, -75.22127 02Sep03 C. b. bartonii 4 50

- - - - - O. obscurus 4 50

119

Sandy Run 60* P 40.12732, -75.16490 27Jun01 P. clarkii 1 100

Elk R - - - - - - -

Big Elk Cr 61 P 39.73004, -75.84828 11May06 O. limosus 1 100

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Table 4.2. Comparison of contemporary (1968-2007) crayfish collections from the northern part of the study area (northern sites) to those from the

southern part of the study area (southern sites). Sites were assigned to the north and south as described in the text and as shown in Figure 4.1. For

individual species and groups of species (all natives, all nonnatives), the number of specimens collected (No. coll), relative abundance (Rel ab),

and number of collection sites and water bodies [No. sites (water bodies)] were reported separately for the northern and southern sites. Abundance

summaries (No. coll, Rel ab) for the northern sites were calculated without data from lower Valley Creek (LVC, sites 50-53) because LVC was

more intensively sampled than the other sites (see Materials and Methods). Thus, inclusion of data from LVC would have biased my abundance

summaries toward C. (P.) sp., which is the dominant crayfish species in LVC. Occurrence summaries [No. sites (water bodies)] for the northern

sites included data from LVC. Due to rounding errors, relative abundances may not sum to exactly 100%. Abbreviations used: P.=Procambarus

(genus) or Puncticambarus (subgenus), O.=Orconectes, and C.=Cambarus. aIncludes 13 Cambarus sp. that

could not be identified to species with

absolute certainty due to their small size but were probably C. b. bartonii.

Northern sites Southern sites

Species No. coll Rel ab (%) No. sites (water bodies) No. coll Rel ab (%) No. sites (water bodies)

C. b. bartonii 194 35.1 17 (16) 75 29.9 14 (13)

C. (P.) sp. 23 4.2 10 (6) 42 16.7 3 (2)

O. limosus 13 2.4 3 (3) 131 52.2 14 (13)

All natives 243a 44.0 24 (20) 248 98.8 21 (17)

O. obscurus 61 11.1 8 (5) 0 0.0 0

O. rusticus 204 37.0 12 (7) 0 0.0 0

O. virilis 31 5.6 3 (3) 1 0.4 1 (1)

P. acutus 2 0.4 1 (1) 1 0.4 1 (1)

P. clarkii 11 2.0 3 (3) 1 0.4 1 (1)

All nonnatives 309 56.0 21 (14) 3 1.2 3 (3)

All species 552 - 37 (25) 251 - 24 (20) 121

122

Figure 4.1. Map of eastern Pennsylvania with an enlargement of the study area and nearby regions in the

southeastern part of the state. Contemporary (1968-2007) crayfish collection sites are denoted by closed circles (●)

and are numbered consecutively according to the scheme provided in Table 4.1. A dashed line separates the northern

and southern parts of the study area. A jagged north/south line denotes the western boundary of the Delaware River

basin. Fawn Run, which is extremely small and flows directly into the Schuylkill River, is completely covered by its

site marker, giving the incorrect, but unavoidable appearance that site 30 is located in the Schuylkill River.

Abbreviations: EB = East Branch, Cr = Creek, R = River.

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Figure 4.2. Map of the study area and nearby regions in southeastern Pennsylvania. Occurrences of C. (P.) sp.,

introduced Orconectes (O. obscurus, O. rusticus, O. virilis), and introduced Procambarus (P. acutus, P. clarkii) are

shown on the map. Sites supporting reproducing populations of C. (P.) sp. are denoted by asterisks (*) and are

referred to as reproductive sites. Other C. (P.) sp. occurrences are denoted by open diamonds (◊) and include sites

without reproducing populations and sites where the reproductive status of the species is unknown. Sites are

numbered according to the scheme provided in Table 4.1. A dashed line separates the northern and southern parts of

the study area. A jagged north/south line denotes the western boundary of the Delaware River basin. Selected dams

located downstream of the reproductive sites are shown on the map and are denoted by symbols. A small, low-

head dam located between sites 52 and 53 on Valley Creek is omitted from the figure to improve clarity. It is

possible that other small dams occur downstream of the reproductive sites unbeknownst to us. Abbreviations: EB =

East Branch, Cr = Creek, R = River.

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Figure 4.3. Map of the study area and nearby regions in southeastern Pennsylvania. Occurrences of C. b. bartonii (C.

bartonii in legend), O. limosus, introduced Orconectes (O. obscurus, O. rusticus, O. virilis), and introduced

Procambarus (P. acutus, P. clarkii) are shown on the map. Sites are numbered according to the scheme provided in

Table 4.1. A dashed line separates the northern and southern parts of the study area. A jagged north/south line

denotes the western boundary of the Delaware River basin. The Green Lane Reservoir dam located in the upper

Perkiomen Creek drainage is shown on the map and is denoted by a symbol. Fawn Run, which is extremely small

and flows directly into the Schuylkill River, is completely covered by its site marker, giving the incorrect, but

unavoidable appearance that site 30 is located in the Schuylkill River. Abbreviations: EB = East Branch, Cr = Creek,

R = River.

125

Figure 4.4. Map of the study area and nearby regions in southeastern Pennsylvania. Occurrences of O. obscurus, O.

rusticus, O. virilis, P. acutus, and P. clarkii are included on the map. Sites are numbered according to the scheme

provided in Table 4.1. A dashed line separates the northern and southern parts of the study area. A jagged

north/south line denotes the western boundary of the Delaware River basin. Abbreviations: EB = East Branch, Cr =

Creek, R = River.

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Chapter 5

Conservation and Management of Crayfishes: Lessons from Pennsylvania

Modified from:

Lieb, D.A., R.W. Bouchard, R.F. Carline, T.R. Nuttall, J.R. Wallace, and C.B. Wengert. 2011.


489-507.

Abstract

North America‘s crayfish fauna is diverse, ecologically important, and highly threatened.

Unfortunately, up-to-date information is scarce, hindering conservation and management efforts.

In Pennsylvania and nearby states, recent efforts allowed me to determine the conservation status

of several native crayfishes and develop management strategies for those species. Due to rarity

and proximity to urban centers and introduced (exotic) crayfishes, C. (P.) sp., an undescribed

member of the Cambarus acuminatus complex, is critically imperiled in Pennsylvania and

possibly range-wide. O. limosus is more widespread; however, recent population losses have

been substantial, especially in Pennsylvania and northern Maryland, where its range has declined

(retreated eastward) by > 200 km. Introduced congeners likely played a major role in those

losses. Although extirpated from some areas, C. b. bartonii remains widespread and is not an

immediate conservation concern. In light of these findings, the role of barriers (e.g., dams),

environmental protection, educational programs, and regulations in preventing crayfish invasions

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and conserving native crayfishes is discussed, and management initiatives centered on those

factors are presented. The need for methods to eliminate exotics and monitor natives is

highlighted. Although tailored to a specific regional fauna, these ideas have broad applicability

and would benefit many North American crayfishes.

Introduction

North America is home to a diverse, ecologically important crayfish fauna that is

threatened by human activities (Master et al. 1998; Wilcove et al. 1998; Lodge et al. 2000a;

Taylor et al. 2007). Until recently, the conservation and management of those species has been a

low priority for most state, federal, and academic institutions. The recent publication of several

large scale conservation assessments, which suggest that about half of North America‘s

crayfishes are imperiled across all or parts of their range (Taylor et al. 1996; Master et al. 1998;

Master et al. 2000; Taylor et al. 2007), greatly increased awareness and interest in the group.

Although more focused efforts in particular regions followed, the accurate classification (e.g.,

vulnerable, secure) of many species remains hampered by a lack of up-to-date distributional and

ecological information (Taylor et al. 2007; Simmons and Fraley 2010). This is problematic

because such classifications often provide the basis for assigning conservation priorities at the

local and national level (Possingham et al. 2002). Thus, incorrect classifications may be costly,

resulting in biodiversity losses and wasted resources.

In Pennsylvania and nearby states, recent efforts combined with historical data (Table

5.1) allowed me to accurately classify most of eastern Pennsylvania‘s native, surface-dwelling

crayfish species: (1) C. b. bartonii; (2) C. (P.) sp., an undescribed member of the Cambarus

acuminatus complex; and (3) O. limosus. My ability to assess changes in the crayfish fauna at

128

individual sites and across the landscape was a key element in this process. I also developed a

number of management strategies that should aid in the conservation of those species.

Because P. clarkii, Cambarus robustus, O. obscurus, O. rusticus, and O. virilis have been

introduced to eastern Pennsylvania and P. acutus has greatly expanded its range in the region as

a result of human activities (Bouchard et al. 2007; Lieb et al. 2007a; Lieb et al. 2011), the aim of

many of these management strategies is to prevent additional crayfish introductions. Successful

prevention is of vital importance because introduced (exotic) crayfishes are one of the biggest

threats to native crayfishes in North America and elsewhere (Lodge et al. 2000a; Taylor 2002;

Taylor et al. 2007). Although stopping the spread of exotic crayfish is difficult once they become

widespread (Peters and Lodge 2009), the distributions of most introduced crayfishes in eastern

Pennsylvania are still limited (Bouchard et al. 2007; Lieb et al. 2007a; Lieb et al. 2011). Thus, in

eastern Pennsylvania, as in much of North America, there is still time to stop the spread of

introduced crayfishes and preserve the native stocks that remain. Although tailored to a specific

fauna, the management strategies presented herein have broad applicability and would likely

benefit many of North America‘s crayfishes, as well as other aquatic invertebrate species of

concern.


Assessing Changes at Individual Sites and Across the Landscape

Eleven sites in the Potomac and Susquehanna drainages of Pennsylvania that historically

supported O. limosus and/or C. b. bartonii were resurveyed (Table 5.2). Nine were from

Ortmann (1906); two were from the United States National Museum, Smithsonian Institution

[USNM 46320 and 48413 (Conoy Creek); USNM 310622 (Penns Creek tributary)]. USNM data

129

included catch numbers for each species; Ortmann‘s data were presence/absence. In most cases,

historical site descriptions were limited to stream and town names, and contemporary collections

were made as close to those towns as possible. The exception was a site whose historical

description was ―tributary of Penns Creek, two miles west of New Berlin.‖ Since the name of the

stream was unknown, I surveyed Sweitzers Run and Tuscarora Creek, the only major Penns

Creek tributaries located < 4.8 km (3 miles) west of New Berlin.

Contemporary collections included a thorough search of multiple riffle-pool sequences

and all available habitat types, which is an effective method for determining community

composition and compiling species lists for individual sites (see Bouchard et al. 2007, Lieb et al.

2007a, and Lieb et al. 2011 for additional details). Historical collection methods are available

from Ortmann (1906) or are unknown (USNM data). Resampling efforts at O. limosus and/or C.

b. bartonii sites in the Delaware basin of Pennsylvania and nearby states are described elsewhere

(Schwartz et al. 1963; Daniels 1998; Kuhlmann and Hazelton 2007; Loughman et al. 2009;

Kilian et al. 2010; Loughman and Welsh 2010; Swecker et al. 2010; Lieb et al. 2011).

Assessments of change at larger scales were possible because of the availability of

contemporary and historical crayfish data from a substantial part of the native ranges of C. b.

bartonii, C. (P.) sp., and O. limosus (see Table 5.1 and range information in Hobbs 1989,

Jezerinac et al. 1995, and Lieb et al. 2011). Coverage of Pennsylvania, Maryland, and West

Virginia was especially complete allowing a particularly clear picture of change in those areas.

To illustrate change in Pennsylvania, maps showing historical and contemporary crayfish

collection sites along with maps of historical and contemporary crayfish distributions were

created (Figures 5.1-5.6; modified from Bouchard et al. 2007). For O. limosus, historical data

were collected prior to 1957 and contemporary data were collected from 1984-2007 (no data

130

available from 1957-1983). For O. obscurus, historical data were collected prior to 1912 and

contemporary data were collected from 1965-2007 (no data available from 1912-1964). For C. b.

bartonii, the data were split approximately in half: historical data were collected prior to 1960

and contemporary data were collected from 1964-2006 (no data available from 1960-1963). For

recent invaders, only contemporary data were available (O. rusticus: 1976-2006, O. virilis: 1986-

2007). Some data could not be mapped because of incomplete site descriptions (e.g., only a

county name provided). Similar maps for Maryland were published by Kilian et al. (2010).

Conservation Classifications

Conservation classifications from published sources and updated classifications

developed for this study are provided in Table 5.3. Published classifications are from the

American Fisheries Society Endangered Species Committee (AFS; Taylor et al. 2007) and the

National Heritage Network (NHN; NatureServe 2010). Updated classifications relied heavily on

range extent, number of populations, changes at individual sites and across landscapes, and

threats to existing populations and were based on criteria and classification definitions provided

by NHN. Due to the availability of historical and contemporary data, I was able to develop

updated classifications for Pennsylvania (Table 5.3); those for Maryland and West Virginia are

provided elsewhere (Kilian et al. 2010; Loughman and Welsh 2010). An updated range-wide

classification is provided for C. b. bartonii. The range-wide status of O. limosus and C. (P.) sp. is

discussed; however, updated classifications at that scale await the completion of additional

taxonomic, genetic, and distributional studies.

131

Conservation Classifications

Cambarus (P.) sp.

Cambarus (P.) sp. was recently discovered in Pennsylvania and has an extremely limited

distribution in the state (Bouchard et al. 2007; Lieb et al. 2007b; Lieb et al. 2008; Lieb et al.

2011). More specifically, the species is only known from 13 sites in a small area (~220 km2) of

southeastern (SE) Pennsylvania. Only four streams (Crum, Darby, Pickering, and Valley creeks)

are known to support populations of C. (P.) sp. One of those populations (Valley Creek) was

recently invaded by O. rusticus and appears to be in decline; the others are located close to dense

populations of several exotic crayfishes, including O. rusticus (Lieb and Bhattarai 2009; Lieb et

al. 2011). All four populations are in a rapidly urbanizing area within ~30 km of one of North

America‘s largest cities (Philadelphia; Lieb et al. 2011).

Outside of Pennsylvania, the C. acuminatus complex occurs in central Maryland,

Virginia, North Carolina, and South Carolina (Meredith and Schwartz 1960; Taylor et al. 2007;

Kilian et al. 2010). C. (P.) sp. is not one of the described species in the complex from North

Carolina and South Carolina (Lieb et al. 2008), where the complex is reasonably well known

(Cooper 2001; Cooper and Cooper 2003; Cooper 2006). Much less is known to the north of the

Carolinas, where additional taxonomic, distributional, and possibly genetic work is needed to

determine whether members of the complex consist of one widely distributed species or multiple

species with more restricted ranges.

Regardless, because historical collections from Pennsylvania do not include the C.

acuminatus complex (Ortmann 1906), C. (P.) sp. is either an introduced species or a recently

discovered native. Generally, the presence of a species where it was historically absent would

132

suggest an introduction; however, historical data are not available for any of the sites where C.

(P.) sp. is found (Ortmann 1906; Lieb et al. 2011).

Some authors cite the presence of disjunct distributions as evidence for crayfish

introductions (Bouchard 1976a; Crocker 1979; Jezerinac et al. 1995). Although the distribution

of the C. acuminatus complex is clearly disjunct with populations in Pennsylvania separated

from those in Maryland by ~125 km (Meredith and Schwartz 1960; Kilian et al. 2010; Lieb et al.

2011), introductions are probably not the cause. First, members of the C. acuminatus complex

(acuminatus species) are not typically introduced outside of their native ranges (Hobbs et al.

1989; Rodriguez and Suarez 2001; Taylor et al. 2007); probably because they are generally not

sold as bait or through biological warehouses. Second, naturally adjacent but disjunct ranges

have been documented for other Puncticambarus species in eastern North America (Hobbs

1969). Third, it is possible that additional populations of the C. acuminatus complex once

occurred in northern Maryland and southern Pennsylvania, but that anthropogenic disturbances

(e.g., crayfish introductions, urbanization) or other physical and biological changes led to their

elimination resulting in the disjunct distribution currently observed. This is especially likely

along the I-95 corridor from Washington D.C. to Philadelphia, which is highly degraded and

infested with exotic crayfishes (see Bouchard et al. 2007, Elmore and Kaushal 2008, and Lieb et

al. 2011). Such a scenario is similar to that suspected for another Puncticambarus species,

Cambarus veteranus, which was believed to occur in two disjunct clusters of sites (one in West

Virginia and one near the border of Virginia and Kentucky) due, at least partly, to the adverse

effects of coal mining in intervening areas (Jezerinac et al. 1995). Finally, it is possible that in

Pennsylvania and Maryland, the range of the C. acuminatus complex is naturally disjunct but

133

that the degree of separation between clusters of sites has been exaggerated by extirpations in

intervening areas.

Given these possibilities, the most likely scenario is that one or more species in the

acuminatus complex once occupied a wider range in Maryland and Pennsylvania [although their

distributions may have always been restricted as is common for species of Puncticambarus

(Hobbs 1969, 1989)], but that human activities reduced the range of the complex to two relic

groups of populations. Therefore, C. (P.) sp. is likely native to Pennsylvania and has a very

limited distribution in the state. The absence of C. (P.) sp. from the historical record is not

surprising given that past surveys did not include some parts of SE Pennsylvania (Ortmann

1906). Thus, although historical surveys were sufficient to characterize the distribution of

widespread species such as O. limosus and C. b. bartonii, very rare ones such as C. (P.) sp. could

have been missed.

Due to rarity and proximity to urban centers and exotic crayfishes, C. (P.) sp. is clearly

imperiled in Pennsylvania (Table 5.3) and in need of conservation attention. In other states,

crayfishes with similarly restricted ranges (known from 9-27 sites) often garner conservation

attention (Taylor and Schuster 2004; Westhoff et al. 2006; Eversole and Welch 2010) and a

number of species of conservation concern in Pennsylvania have wider distributions and are less

threatened than C. (P.) sp. (see Felbaum et al. 1995). Although undescribed, the lack of a specific

epithet should not prevent C. (P.) sp. from being a conservation priority (see Bouchard 1976b,

Harris 1990, Jelks et al. 2008, and others, which included undescribed species in lists of

imperiled crayfishes and fishes).

If the acuminatus species in Pennsylvania is different from those to the south, then range-

wide conservation attention and inclusion on lists of globally imperiled species (e.g., AFS, NHN)

134

may be warranted, as has already been done for two acuminatus species (Cambarus hystricosus,

Cambarus johni) known from ~25-55 locations (Cooper and Cooper 2003; Cooper 2006; Taylor

et al. 2007; Simmons and Fraley 2010). Even if the Pennsylvania acuminatus species occurs

elsewhere, such actions may be justified if Pennsylvania populations exhibit adaptations not

present to the south making them important for maintaining the genetic variability of the species

(see Hamr 1998 for similar discussions regarding Canada‘s crayfishes and Hunter and

Hutchinson 1994 and Lesica and Allendorf 1995 for more general discussions of the value of

peripheral populations). Additionally, given the restricted distribution of the C. acuminatus

complex in Maryland (< 10 occurrences since 1989 and < 30 overall; see Figure 4 of Kilian et al.

2010), even if the species in Pennsylvania is the same as that in Maryland, broader scale actions

may be warranted. Overall, C. (P.) sp. is probably one of the most endangered aquatic species in

the state and possibly in eastern North America (if its range is limited to Pennsylvania) and,

without management action, faces an uncertain future.

Orconectes limosus

Although O. limosus records exist for a large swath of the Atlantic drainage of eastern

North America (Virginia northward to Canada; Ortmann 1906; Crocker 1957; Francois 1959;

Meredith and Schwartz 1960; Crocker 1979; Hobbs 1989; McAlpine et al. 1991; Jezerinac et al.

1995; Lambert et al. 2007), recent large scale surveys indicate that the species has been

extirpated from a substantial part of its former range. For example, in Pennsylvania, the range of

O. limosus has declined (retreated eastward) by ~225 km and the species has nearly been

eliminated from the Susquehanna and Potomac basins (Figure 5.2; Bouchard et al. 2007).

Resampling efforts at or near historical sites in those basins yielded hundreds of introduced

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congeners but no O. limosus (Table 5.2 herein and Table 1 of Bouchard et al. 2007). Except for

the presence of O. limosus in a few tributaries of the North Branch Potomac River, similar range

reductions have occurred in northern Maryland (Kilian et al. 2010). The prevalence of introduced

congeners in areas that lost populations of O. limosus suggests that crayfish introductions likely

played a major role in those losses (Figures 5.2-5.5; Table 5.2; Bouchard et al. 2007; Kilian et al.

2010); although other factors may have also been important.

More focused efforts in the Patapsco drainage of Maryland, the upper Susquehanna

drainage of New York, the Potomac drainage of West Virginia, and the lower Delaware drainage

of Pennsylvania also documented the frequent replacement of O. limosus by introduced

congeners (Schwartz et al. 1963; Kuhlmann and Hazelton 2007; Loughman et al. 2009;

Loughman and Welsh 2010; Swecker et al. 2010; Lieb et al. 2011). Because the lower Delaware

drainage of Pennsylvania and nearby areas are an important reservoir of genetic variability for O.

limosus (Filipová et al. 2011), extirpations from that area may have implications for the long-

term viability and conservation status of O. limosus in the state and the region (see Ehrlich and

Daily 1993, Fetzner and Crandall 2002, and Luck et al. 2003 for discussions of the importance of

genetic variability to species persistence).

These findings prompted Bouchard et al. (2007) to speculate that O. limosus may

eventually be eliminated from the Piedmont of Pennsylvania and Maryland, persisting only in the

Coastal Plain where it may be better able to compete with introduced crayfishes. Unfortunately,

Pennsylvania‘s Coastal Plain is small, densely populated, and extensively modified (Bouchard et

al. 2007), with additional alterations likely. Maryland‘s Coastal Plain is larger and less populated

but also has a substantial human footprint (King et al. 2005; Utz et al. 2010), which will

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undoubtedly increase as the region‘s population centers, including Washington, D.C. and

Baltimore, continue to expand.

Although recent losses have been substantial, it is important to note that some of the

populations that have been lost from the mid-Atlantic may not have been native to begin with

(see Ortmann 1906 and Bouchard et al. 2007 for discussions of the potential influence of man-

made canals on O. limosus dispersal). Nonetheless, given the magnitude of the losses and the

threats O. limosus faces, the populations that remain in Pennsylvania and Maryland have

significant conservation value at the state and regional level.

This is ironic given that O. limosus has been introduced to Europe and Canada and has

rapidly expanded its range, often at the expense of native crayfishes (Hamr 1998; Lambert et al.

2007; Taylor et al. 2007). As a result, O. limosus is viewed as a pest across much of its nonnative

range (Hamr 2002; Filipová et al. 2011). Nonetheless, the conservation of native O. limosus is

warranted because introduced populations lack the genetic diversity that is present in native

stocks (Filipová et al. 2011).

Thus, although O. limosus is listed as globally secure/stable by AFS and NHN (Table

5.3), recent findings indicate that native stocks may not be as safe as previously thought. In

Pennsylvania, range reductions and the threat posed by exotic crayfishes prompted me to

downgrade O. limosus from ‗Apparently Secure‘ to ‗Vulnerable‘ (Table 5.3). In West Virginia,

O. limosus is listed as ‗Critically Imperiled‘ and may have been eliminated from the state by

exotic crayfish (Loughman and Welsh 2010; Swecker et al. 2010). In Maryland, O. limosus is

listed as ‗Demonstrably Secure‘ but the species is threatened by exotic crayfish and significant

range reductions have occurred in recent years (Kilian et al. 2010). Additional surveys along

with genetic work are needed to update the status of O. limosus in other regions and across its

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range. Overall, this assessment suggests that management intervention is likely needed to ensure

the continued existence of O. limosus in Pennsylvania and possibly elsewhere in its native range

and illustrates the importance of periodically reevaluating the status of native crayfishes (even

widespread ones).

Cambarus b. bartonii

Although the range of C. b. bartonii has remained relatively stable over the past century

in Pennsylvania and Maryland (Figure 5.6; Bouchard et al. 2007; Kilian et al. 2010; Lieb et al.

2011), the species has been replaced by introduced crayfishes at some locations in those states

and New York (Table 5.2; Schwartz et al. 1963; Daniels 1998; Kuhlmann and Hazelton 2007).

Additionally, C. b. bartonii may be negatively affected by nonnative O. virilis in eastern West

Virginia (Swecker et al. 2010) and is in serious decline in parts of Ontario, Canada, although

introduced crayfishes are not the cause (Edwards et al. 2009).

Given this information and the continued expansion of introduced crayfishes in eastern

North America, additional losses appear likely. Fortunately, because C. b. bartonii is widely

distributed in eastern North America from Canada southward to Georgia and is still common in

many areas (Hobbs 1989; Bouchard et al. 2007; Kilian et al. 2010; Loughman and Welsh 2010;

Simmons and Fraley 2010), these losses do not pose an immediate threat to the species.

However, it is possible that extirpations may eventually reduce the genetic variability and long-

term viability of C. b. bartonii in some areas. Although such concerns are often expressed for

species with restricted ranges and small population sizes, even widespread crayfish species can

suffer substantial reductions in genetic variability due to anthropogenic disturbances (Buhay and

Crandall 2005). Nonetheless, because resources are limited, it is important to emphasize that C.

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b. bartonii is not an immediate conservation concern regionally or globally (Table 5.3; Kilian et

al. 2010; Loughman and Welsh 2010; Simmons and Fraley 2010).

Management Needs and Implications

Given the imperiled status of C. (P.) sp. and O. limosus in Pennsylvania and elsewhere,

efforts to prevent crayfish introductions and preserve the habitat and water quality at sites that

support those species should be a management priority. In subsequent sections, I describe

regulatory, educational, and conservation initiatives, which should aid in this regard. I also

discuss the need for methods to safely eradicate introduced crayfishes; however, the successful

development of such methods will not eliminate the need for policies aimed at preventing

introductions, which should remain the first line of defense. Although most specific examples are

from Pennsylvania, the general concepts and management strategies that are provided have broad

applicability and would likely benefit many of North America‘s crayfishes, as well as other

aquatic invertebrate species of concern.

Crayfish Ban

Because introduced crayfishes occur in a number of water bodies in Pennsylvania

(Bouchard et al. 2007; Lieb et al. 2007a; Lieb et al. 2011) and are available from bait shops,

biological warehouses, pet stores, live food vendors, and aquaculture facilities, which are, at

best, loosely regulated, it would be difficult to prevent additional introductions in Pennsylvania

without further regulations and their enforcement (see Lodge et al. 2000a, b; Burkholder and

Wallace 2001; and DiStefano et al. 2009). Although O. rusticus has been tightly regulated since

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2005 and cannot be possessed, sold, transported, or cultured within the state (58 Pa Code §

71.6.d 2008; PFBC 2009), other introduced crayfishes (P. acutus, C. robustus, O. obscurus, O.

virilis) are unregulated and can be purchased from commercial dealers or collected from invaded

water bodies and released legally into the state‘s waters. Additionally, although P. clarkii cannot

be propagated in flow-through systems or introduced into Pennsylvania waters (PFBC 2009), the

species is cultured in parts of Pennsylvania and can be possessed, sold, and transported legally

within the state. This situation is not unusual because many places in North America do not

strictly regulate all their introduced or potentially introduced crayfish species (DiStefano et al.

2009; Peters and Lodge 2009).

Strict regulations that only apply to a few species will not prevent crayfish introductions

in most areas. Extending existing bans to other species would be hard to enforce because most

natural resource managers and conservation officers have difficulty identifying crayfish (Lodge

et al. 2000b; Peters and Lodge 2009). For this reason, banning the possession, sale,

transportation, and culture of all native and nonnative crayfishes in Pennsylvania and elsewhere

(a complete ban) is warranted. Such a ban would make it illegal to use live crayfish as bait as

recommended by Lodge et al. (2000b) and DiStefano et al. (2009) and as is already the case in

Wisconsin, Virginia and parts of Maryland and Canada (Taylor et al. 2007; DiStefano et al.

2009; MDDNR 2009). The Wisconsin ban, enacted in 1983, received nearly universal approval

from the public (comments 5:1 in favor of it), ―caused no unusual controversy, and has not

caused any apparent harm to Wisconsin‘s important fishing industry‖ (Lodge et al. 2000b:23).

Due to my outreach efforts, including at least 13 articles in the popular media (newspapers,

magazines, internet) since 2004, and those of the Pennsylvania Sea Grant, residents of

Pennsylvania are becoming increasingly aware of the threat that introduced crayfishes pose and

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would likely support a crayfish ban. Outreach efforts are also underway elsewhere (DiStefano et

al. 2009; Kilian et al. 2010), increasing the likelihood that a complete ban would be supported by

the public.

Ideally, the complete ban would apply to all water bodies; however, it may be possible to

permit the use of crayfish as bait in selected locations that are already infested with introduced

crayfish (a partial ban). Such a measure would maintain a ban on the sale, transportation, and

culture of crayfish but allow anglers to collect and fish with crayfish at some infested locations

(exempt sites). Because some noncompliance may occur (DiStefano et al. 2009), exempt sites

should not be in the vicinity of imperiled crayfish. For example, substantial reaches of the

Schuylkill River in Pennsylvania are completely dominated by introduced O. rusticus (Lieb et al.

2011) and would, in theory, qualify for exempt status. However, because those reaches are in the

vicinity one of Pennsylvania‘s rarest crayfish [C. (P.) sp.; Lieb et al. 2011], they should not be

exempt. Locations that have never been surveyed for crayfishes or have not been surveyed

recently should also not be exempt. Although not risk-free, a partial ban would provide

recreational opportunities for anglers that use crayfish as bait while still reducing the chance of

introductions.

Some will likely argue that anglers should be allowed to collect and fish with crayfish

wherever they choose (not just at exempt sites), as long as crayfish are not moved from place to

place. However, such a measure; which makes sense in theory and would allow crayfish to be

possessed but not sold, transported, or cultured; would be difficult to enforce. This is because

unless an individual is caught transporting, selling, or culturing crayfish it would be impossible

to determine if a violation has occurred. In contrast, a complete or partial ban would be much

easier to enforce because anglers would either not be allowed to use crayfish as bait anywhere

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(complete ban) or would only be permitted to use them in certain waters (partial ban). Under a

complete or partial ban, the job of law enforcement would be to prevent anglers from using

crayfish as bait in restricted waters, which is much easier than trying to determine if crayfish are

being transported between sites.

Education and Outreach

Although education and outreach programs targeting policy makers and the general

public are vitally important in preventing crayfish introductions (Lodge et al. 2000b; Hamr 2002;

Taylor 2002), until recently there was little up-to-date information to dispense in many areas,

including Pennsylvania. Nonetheless, when this information became available in Pennsylvania,

the state‘s regulatory agencies moved quickly, enacting a ban on O. rusticus in 2005, within

approximately a year of being informed of the extent of the infestation. The general public has

proven equally as responsive; providing crayfish specimens, helping to detect new invasions

(also noted by Lodge et al. 2006), and urging the passage of additional regulatory measures to

prevent introductions.

To date, most outreach efforts in Pennsylvania have been restricted to articles in the

popular media, invasive species workshops, and presentations at scientific and management

meetings. Although productive, the effectiveness of those efforts could be increased by targeting

vulnerable areas (watersheds that support imperiled species and/or are at risk of invasion) and

potential sources of exotics including bait shops, biological warehouses, pet stores, live food

vendors, and aquaculture facilities (see Burkholder and Wallace 2001, Puth and Allen 2004,

Keller et al. 2008, and DiStefano et al. 2009). Town-hall style gatherings in vulnerable areas and

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attempts to educate anglers and others that contact crayfish would likely extend current efforts to

a different subset of the public.

The placement of warning signs along water bodies that support imperiled crayfish such

as C. (P.) sp. and O. limosus (to prevent introductions) and along heavily infested waterways (to

prevent the transfer of exotics elsewhere) would probably slow the spread of exotics, particularly

in heavily fished areas. To decrease costs, signs could be strategically placed at boat launches

and other popular access points.

Role of Dams, Temperature, and Nutrients

Although the susceptibility of individual sites to crayfish invasions is potentially

influenced by a number of factors (Kershner and Lodge 1995; Light 2003; Usio et al. 2006;

Phillips et al. 2009; Capinha and Anastacio 2011); in this section, I focus on dams, temperature,

and nutrients because they appear to be important for one of Pennsylvania‘s rarest crayfish [C.

(P.) sp.; Lieb and Bhattarai 2009; Lieb et al. 2011] and have the potential to influence invasions

in many areas.

The ecological benefits of dam removal have been thoroughly discussed in the scientific

literature and are a major reason for the recent surge in removal projects; however, the negative

effects of such removals have received much less attention and are typically limited to the

downstream transport of sediments, nutrients, and toxic materials and the upstream movement of

introduced fish (Bednarek 2001; Bushaw-Newton et al. 2002; Hart et al. 2002; Poff and Hart

2002; Stanley and Doyle 2003). Because dams can block the dispersal of crayfish (Meyer et al.

2007), their removal may facilitate crayfish invasions in some systems, with the potential for

negative effects on native communities. Despite this possibility, the potential for such effects is

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rarely discussed in the scientific literature (but see Kerby et al. 2005 and Bubb et al. 2008), or

empirically tested, and is typically not considered by regulatory agencies charged with managing

dam removals.

Continuing to ignore the potential influence of dams on crayfish invasions could have

serious consequences, particularly for imperiled crayfishes. For example, in Pennsylvania, dams

are located downstream of most of the known populations of an extremely rare crayfish [C. (P.)

sp.] and may be protecting them from invasion (especially by O. rusticus; Lieb et al. 2011). At a

minimum, surveys should be conducted prior to dam removal to ensure that removal will not

facilitate the upstream migration of introduced crayfish. Ironically, dams that are protecting

upstream areas from invasion may need to be left in place for conservation reasons. In areas

prone to invasion, dams located downstream of imperiled crayfish should probably not be

removed, regardless of whether exotics are present in the system or not.

Low temperatures may also play a role in protecting some uninvaded sites. For example,

in Pennsylvania, water temperatures at sites with populations of C. (P.) sp. [hereafter termed C.

(P.) sp. sites] are likely lower than that preferred by O. rusticus, possibly delaying or preventing

its establishment at those sites (Lieb and Bhattarai 2009). Support for this possibility is provided

by Mundahl and Benton (1990), who determined that O. rusticus growth was maximized at 26-

28 °C in laboratory experiments and predicted that the species would be most successful in

systems with average summer water temperatures near that range. Stream surveys in Ohio, which

indicated that O. rusticus was more successful in warmer, downstream reaches that remain above

20 °C throughout the summer than in cooler headwater areas (Jezerinac 1986; Mundahl and

Benton 1990; Thoma and Jezerinac 2000), appear to support their prediction. Because

temperatures at C. (P.) sp. sites are known or suspected to be <20 °C for substantial parts of the

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summer (Steffy and Kilham 2006; Lieb and Bhattarai 2009), it is possible that O. rusticus has

been slow to invade those sites, at least partly, because relatively low temperatures afford

resident species a bioenergetic advantage over O. rusticus (see Momot et al. 1988 for a similar

example).

The recent discovery of O. rusticus at the Valley Creek C. (P.) sp. sites suggests that,

although not favored by O. rusticus, low temperatures may not prevent invasions indefinitely.

The spread of O. rusticus into the northern United States and Canada (Hamr 2002; Taylor et al.

2007; Phillips et al. 2009) further indicates that low temperatures alone may not provide a

permanent barrier against invasion. It is also possible that, in Valley Creek, recent temperature

increases resulting from urbanization (Steffy and Kilham 2006) have tipped the bioenergetic

balance in favor of O. rusticus. Mundahl and Benton (1990) and Whitledge and Rabeni (2002)

voiced similar concerns regarding the potential influence of habitat and climate-driven changes

in temperature on O. rusticus invasions in Ohio and Missouri. Additional temperature increases

in Valley Creek and the other C. (P.) sp. sites are likely due to continued urbanization (Steffy

and Kilham 2006; Kaushal et al. 2010), increasing regional ground water temperatures

(Eggleston et al. 1999), and climate change (see Mohseni et al. 1999, Chang 2003, and Kaushal

et al. 2010). Such increases may eventually result in thermal conditions in many areas, including

the C. (P.) sp. sites, which favor O. rusticus.

The relatively low nutrient status of the C. (P.) sp. sites (oligo-mesotrophic; Lieb and

Bhattarai 2009) is probably not optimal for O. rusticus, which —due to its high metabolic rate,

high growth rate, and large size —tend to do best in productive systems where nutrients are

plentiful (Momot 1984; Momot et al. 1988). However, continued urbanization of the

Philadelphia suburbs will likely increase nutrient levels at the C. (P.) sp. sites in the future (see

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Lenat and Crawford 1994 and Carpenter et al. 1998). Additionally, it has been predicted that, as

atmospheric CO2 levels rise, SE Pennsylvania will become warmer and wetter, further increasing

nutrient loading from urbanizing basins in the region (Chang 2004). Elevated nutrient levels may

increase the likelihood of future O. rusticus invasions at the C. (P.) sp. sites and other locations

that are not highly enriched, as appears to have already occurred in Ohio and West Virginia

(Jezerinac et al. 1995; Thoma and Jezerinac 2000).

These data suggest that barriers (dams, low temperatures, low nutrients) are likely

preventing or slowing exotic crayfish from invading some sites in Pennsylvania that support

imperiled crayfish. Unfortunately, dam removals and expected increases in water temperature

and nutrient levels resulting from climate change and urbanization may compromise or weaken

those barriers in the future. More generally, these findings highlight the potentially important but

often overlooked role that physical and chemical barriers of natural and anthropogenic origin

play in preventing crayfish invasions. Ultimately, the preservation of native crayfish in some

heavily infested areas may depend on management efforts that maintain, strengthen, or expand

existing barriers.

Eliminating Exotics

Although the negative effects of introduced crayfish are well documented, little is known

about how to eliminate them from invaded waters. Chemical poisons are available; however,

native crayfish are also killed (Gunderson 2008). Intensive harvesting may reduce population

sizes, but is laborious and unlikely to result in eradication (Hamr 1999; Holdich et al. 1999;

Freeman et al. 2010). In a Wisconsin lake, O. rusticus densities were dramatically reduced

(although extirpation was not achieved) using a combination of trapping and increased fish

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predation (Hein et al. 2007). Unfortunately, the effort required was substantial and similar results

in open systems (streams) are not assured. Pheromone baits could potentially reduce this effort

by increasing trap efficiency (Holdich et al. 1999; Freeman et al. 2010) but are still in the early

stages of development (Stebbing et al. 2003; Aquiloni and Gherardi 2010). These difficulties

have led many authors (e.g., Lodge et al. 2000b; Hamr 2002; Gunderson 2008) to conclude that

introduced crayfish can best be controlled by preventing future introductions.

Although I agree with this reasoning, additional introductions are likely unavoidable. As

a result, the persistence of certain native crayfishes [particularly those with limited ranges such

as C. (P.) sp.] may require the removal of exotics. Unfortunately, species-specific treatments that

eliminate introduced crayfish with minimal effects on nontarget species are currently not

available (Lodge et al. 2000b; Gunderson 2008; Freeman et al. 2010). Their development should

be possible; however, because crayfish species vary in their response to a variety of substances

(Hobbs and Hall 1974; Berrill et al. 1985; Eversole and Seller 1996; Nyström 2002; Wigginton

and Birge 2007). Additionally, because molting crayfish are especially sensitive to toxicants

(Wigginton and Birge 2007), it may be possible in some situations to apply treatments when

exotics are at the peak of their molting cycle but natives are not to minimize effects on nontarget

species. The release of sterilized males, which has long been used to control insect pests (Myers

et al. 2000) but has only recently been considered for crayfish (Holdich et al. 1999; Aquiloni et

al. 2009), endocrine disruptors, which interfere with molting and reproductive processes in

crustaceans (Rodriguez et al. 2007; Mazurova et al. 2008), and species-specific pathogens

(Holdich et al. 1999; Davidson et al. 2010; Freeman et al. 2010) might also be effective for

crayfish.

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The objective of most treatment programs would be eradication; although for some

abundant, highly fecund invaders such as O. rusticus, population control may be more feasible

(Myers et al. 2000). Because introduced species are difficult to eradicate if well established

(Myers et al. 2000; Lodge et al. 2006), watersheds that support imperiled crayfish should be

routinely monitored (at least once per year) to ensure that invasions are detected quickly (see

similar, albeit less specific, recommendations in Lodge et al. 2006). Given that

eradication/control programs require public support and can be controversial, particularly if

chemicals are used in populated areas, such efforts should include outreach and public education

initiatives (Myers et al. 2000; Genovesi 2005). Due to the presence of C. (P.) sp. and recent

invasion by O. rusticus, Valley Creek would be an obvious candidate for treatment.

Eradication/control programs could be combined with restocking efforts to restore native

crayfishes to systems where they have been extirpated.

Reducing Environmental Degradation

Anthropogenic disturbances and associated declines in habitat and water quality are a

serious threat to North America‘s native crayfishes (Wilcove et al. 1998; Guiaşu 2002; Taylor et

al. 2007). Many of these disturbances can be related directly or indirectly to landscape scale

changes associated with agricultural and urban development. As a result, the preservation of

native crayfish should include efforts to preserve natural areas, particularly in the riparian zone

(Burskey and Simon 2010), and mitigate existing impacts. Riparian forests may be of particular

value because they reduce pollutant, sediment, and nutrient loading (Lowrance et al. 1984;

Peterjohn and Correll 1984; Pinho et al. 2008); lower water temperature (Burton and Likens

1973; Barton et al. 1985; Storey and Cowley 1997); and provide refugia from flooding (in the

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form of tree roots and woody debris; Smith et al. 1996; Parkyn and Collier 2004), which would

benefit crayfish communities directly via improved habitat and water quality and indirectly by

reducing the likelihood of crayfish invasions (see ‗Role of dams, temperature, and nutrients‘

section). In Pennsylvania, such benefits are particularly likely for C. (P.) sp. because it is

typically found in streams with relatively low temperatures and nutrients and appears to be

negatively affected by sedimentation and introduced crayfish (Lieb et al. 2008; Lieb and

Bhattarai 2009; Lieb et al. 2011). Nonetheless, because the benefits of riparian forests are not

always apparent (particularly in highly developed areas; Roy et al. 2005, 2006, 2007), their

presence alone will not necessarily assure the long-term survival of native crayfish.

In Pennsylvania, exceptional value (EV) status affords surface waters protection under

state law and mandates that ―water quality be maintained and protected‖ (25 Pa Code § 93.4a

2007). Surface waters qualify for EV status if they are of ―exceptional ecological significance‖,

defined as ―important, unique, or sensitive ecologically‖ (25 Pa Code § 93.1 2007). Although

surface waters that support imperiled crayfish such as C. (P.) sp. and O. limosus appear to meet

those criteria, most are not classified as EV and need to be reevaluated [especially those with C.

(P.) sp.]. More generally, whenever possible, imperiled crayfish should be considered when

surface waters are classified and antidegradation priorities are assigned.

Because urban areas support imperiled crayfish and are crisscrossed by pipelines,

railroads, and roadways that serve as conduits for wastes and toxic materials, efforts to prevent

spilled materials from reaching imperiled crayfish are needed. Those efforts should include the

diversion of road runoff away from populations of imperiled crayfish and the frequent inspection

and maintenance of pipelines, railroads, and roadways that are in the vicinity of those

populations. In Pennsylvania, such safeguards are especially pertinent to C. (P.) sp. because

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underground sewage conduits occur upstream of many C. (P.) sp. sites (Ryan and Packman

2006). Further, some of the largest and busiest highways and railroads in Pennsylvania are in the

vicinity of those sites and are a major supply route for chemicals, fuels, and other toxic materials

coming in and out of the Philadelphia area. Therefore, spills in this region could have serious

consequences for C. (P.) sp. In recent years, at least two substantial releases of diesel fuel from

tanker trucks involved in highway accidents have occurred downstream of C. (P.) sp. sites

(National Response Center 2002; Schaefer and Mastrull 2007). Given the continued expansion of

urban areas in SE Pennsylvania, future spills, including those upstream of C. (P.) sp. sites, seem

likely.

Additional Sampling

Because O. limosus and C. (P.) sp. are imperiled in Pennsylvania and elsewhere, efforts

to better define their ranges and monitor populations are needed. Range refinement will require

crayfish collections from watersheds that have not been sampled recently and more sampling of

drainages that currently support C. (P.) sp. and O. limosus. Once their distributions have been

refined, range-wide monitoring programs can be developed. Efforts to quickly detect crayfish

invasions and relate population sizes to conditions at the reach scale (e.g., instream habitat) and

basin scale (e.g., land use) should be included in those programs. Regular monitoring should

allow population declines to be detected and causative factors identified, ultimately providing the

information needed to protect C. (P.) sp. and O. limosus across their ranges. Initiatives of this

type should have widespread applicability, assisting efforts to conserve crayfish in a variety of

settings.

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Acknowledgments

I thank Nellie Bhattarai, Hannah M. Ingram, and Jeremy Harper for their substantial

contributions. The Wild Resources Conservation Fund, Pennsylvania Department of

Conservation and Natural Resources (Project Number AG050523); the National Park Service

(Grant Agreement H4560030064); and a Pennsylvania State Wildlife Grant (number

PFBC050305.01) provided financial support. Christopher A. Urban, Matt R. Marshall, and Sarah

Nichols administered grants and provided encouragement. Emily and Megan Lieb assisted in the

field at some sites. Patrick Martinez, an anonymous reviewer, and Marybeth Lieb provided

helpful critiques of the paper.

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Table 5.1. Historical and contemporary crayfish studies that aided in the development of the conservation

classifications (e.g., vulnerable, secure) and management strategies provided herein. Studies are listed by state (US)

or province (Canada). Statewide refers to studies that include most of the state; NPS=National Park Service,

PA=Pennsylvania.

State/Province Coverage Source

Historical

Maryland Statewide Meredith and Schwartz 1960

Patapsco River drainage Schwartz et al. 1963

New York Statewide Crocker 1957

Pennsylvania Statewide Ortmann 1906

Statewide Bouchard et al. 2007a

West Virginia Northern part of the state Ortmann 1906

Contemporary

Maryland Statewide Kilian et al. 2010

New York Upper Susquehanna River drainage Kuhlmann and Hazelton 2007

Schoharie Creek drainage Daniels 1998

North Carolina Western part of the state Simmons and Fraley 2010

Pennsylvania Statewide with emphasis on eastern PA Bouchard et al. 2007

NPS properties across the state Lieb et al. 2007a

Valley Creek Lieb et al. 2007b

Valley Creek Lieb et al. 2008

Southeastern part of the state Lieb and Bhattarai 2009

Southeastern part of the state Lieb et al. 2011

West Virginia Statewide Jezerinac et al. 1995

Statewide Loughman et al. 2009

Statewide Loughman and Welsh 2010

Eastern Potomac River drainage Swecker et al. 2010

Ontario south-central part of the province Edwards et al. 2009

aIncludes historical museum records.

Table 5.2. Historical and contemporary crayfish collections from resampled sites in the Susquehanna (S) and Potomac (P) River drainages of Pennsylvania.

Historical data were collected in 1912 (Conoy Creek), 1956 (Penns Creek tributary), or were taken from Ortmann (1906), who did not provide collection dates

for individual sites. Contemporary data were collected in 2006 and 2007. Abbreviations used: R=Raystown, Br=Branch, Cr=Creek, R=River, Trib=Tributary,

NA=Not available, bartonii=C. b. bartonii, limosus=O. limosus, obscurus=O. obscurus, rusticus=O. rusticus, virilis=O. virilis.

Stream

Lat, Long Historical

Contemporary

(drainage) County Nearby town (decimal °) Species n

Species n

Back Cr (P) Franklin Williamson 39.85422, -77.79622 limosus NA

virilis 18

Conococheague Cr (P) Franklin Chambersburg 39.96102, -77.64832 bartonii NA

bartonii 1

limosus NA

obscurus 8

virilis 11

Conococheague Cr (P) Franklin Williamson 39.84675, -77.79425 limosus NA

bartonii 1

obscurus 10

virilis 37

Bald Eagle Cr (S) Centre Milesburg 40.94309, -77.78700 bartonii NA

obscurus 25

limosus NA

Conoy Cr (S) Lancaster Bainbridge 40.08473, -76.66097 bartonii 20

rusticus 82

Conodoquinet Cr (S) Cumberland West Fairview 40.25543, -76.92745 limosus NA

rusticus 22

Fishing Cr (S) Columbia Bloomsburg 40.99537, -76.47353 limosus NA

obscurus 26

Montour Cr (S) Perry Green Park 40.35842, -77.31798 bartonii NA

obscurus 3

limosus NA

rusticus 55

R Br Juniata R (S) Bedford Bedford 40.02013, -78.50278 limosus NA

obscurus 7

Trib of Penns Cr (S) Union/Snyder New Berlin 2 possibilitiesa limosus 1

bartonii 10b

obscurus 17b

rusticus 56b

Yellow Breeches Cr (S) Cumberland/York New Cumberland 40.22395, -76.86070 limosus NA

rusticus 39 a40.87208, -77.01345 (Sweitzers Run) or 40.86767, -77.00650 (Tuscarora Creek); see methods for further explanation.

bTotal for Sweitzers Run and Tuscarora Creek.

167

168

Table 5.3. Conservation classifications for several of eastern

Pennsylvania's native crayfishes. Abbreviations used: CS=Currently

stable; G5, S5 (species classification) and T5 (subspecies

classification)=Secure; S4=Apparently secure; S3=Vulnerable;

S1=Critically imperiled; NL=Not listed; AFS=American Fisheries

Society; NHN=National Heritage Network; C.=Cambarus;

O.=Orconectes; b.=bartonii; P.=Puncticambarus. Updated

classifications were developed for this study. An asterisk (*)

indicates that more information is needed to update the

classification. See methods for further explanation of classification

procedures and sources.

Global

Pennsylvania

Species AFS NHN Updated

NHN Updated

C. b. bartonii CS G5T5 G5T5

S5 S5

C. (P.) sp. NL NL *

NL S1

O. limosus CS G5 *

S4 S3

169

Figure 5.1. Map of Pennsylvania with historical and contemporary crayfish collection sites. Sites

from Ortmann (1906) are plotted separately from the remaining historical data. Collection dates

were not available for some sites (Unknown Year). From east to west, the Delaware,

Susquehanna, Potomac, Genesee, and Ohio River drainages are delineated. The Lake Erie

drainage is shown in the northwest corner of the map. For simplicity, streams that flow directly

into the Chesapeake Bay are included in the Susquehanna drainage.

Figure 5.2. Map of eastern Pennsylvania with historical and contemporary O. limosus collection sites. Sites from Ortmann (1906) are plotted separately from the

remaining historical data. From east to west, the Delaware, Susquehanna, and Potomac River drainages are delineated. For simplicity, streams that flow directly

into the Chesapeake Bay are included in the Susquehanna drainage. Historical O. limosus sites in the Susquehanna and Potomac drainages that were resurveyed

for crayfishes are circled; O. limosus was not found at any of them. Because the Back and Conococheague Creek sites near the town of Williamson (Potomac

drainage) are close together, their site markers overlap. See Table 5.2 and methods for additional details.

170

Figure 5.3. Map of eastern Pennsylvania with historical and contemporary O. obscurus collection sites. The Ortmann (1906) site is plotted separately from the

other historical site. From east to west, the Delaware, Susquehanna, and Potomac River drainages are delineated. For simplicity, streams that flow directly into

the Chesapeake Bay are included in the Susquehanna drainage. See Table 5.2 and methods for additional details.

171

Figure 5.4. Map of eastern Pennsylvania with O. rusticus collection sites. From east to west, the Delaware, Susquehanna, and Potomac River drainages are

delineated. For simplicity, streams that flow directly into the Chesapeake Bay are included in the Susquehanna drainage. See Table 5.2 and methods for

additional details.

172

Figure 5.5. Map of eastern Pennsylvania with O. virilis collection sites. From east to west, the Delaware, Susquehanna, and Potomac River drainages are

delineated. For simplicity, streams that flow directly into the Chesapeake Bay are included in the Susquehanna drainage. Because the Back and Conococheague

Creek sites near the town of Williamson (Potomac drainage) are close together, their site markers overlap. See Table 5.2 and methods for additional details.

173

Figure 5.6. Map of eastern Pennsylvania with historical and contemporary C. b. bartonii collection sites. Sites from Ortmann (1906) are plotted separately from

the remaining historical data. From east to west, the Delaware, Susquehanna, and Potomac River drainages are delineated. For simplicity, streams that flow

directly into the Chesapeake Bay are included in the Susquehanna drainage. Historical C. b. bartonii sites in the Susquehanna and Potomac drainages that were

resurveyed for crayfishes are enclosed by circles; C. b. bartonii was not found at three of them. See Table 5.2 and methods for additional details.

174

175

Chapter 6

Determinants of Crayfish Community Structure

Introduction

The factors responsible for local community structure have long been debated by

ecologists. Frederic E. Clements (Clements 1916, Clements et al. 1929) supposed that

communities were tightly linked groups of species (complex organisms), implying that local

interactions (e.g., competition, predation, mutualism) were important in determining their

structure. Henry A. Gleason (Gleason 1926) opposed this view, instead arguing that communities

were chance assemblages of individually distributed species that occurred together at particular

points in space and time due to their need for similar environmental conditions, implying weak

local interactions. Robert A. MacArthur and colleagues (e.g., MacArthur 1965, MacArthur and

Levins 1967) built on earlier work by Grinnell (1917), Lotka (1925), Volterra (1926), Elton

(1927), Gause (1934), Hutchinson (1957) and others and ushered in the era of local determinism,

in which local interactions occurring in ecological time were thought to largely determine local

community structure. In this view, local processes such as competition, predation, and

mutualism, preceded to equilibrium rapidly, negating the importance of processes operating at

larger scales (Ricklefs 2008). Local determinism predicts that local communities should be

saturated with species, and that local species richness should be independent of regional species

richness (Terborgh and Faaborg 1980).

176

This view persisted for several decades until ecologists, most prominently Robert E.

Ricklefs (Ricklefs 1987), began to argue for the importance of regional and historical factors in

determining local community structure. Plots of local verses regional species richness, which

were often found to be linear (Lawton 1999, Loreau 2000, Mouquet et al. 2003), suggesting that

local communities were unsaturated and that regional and historical factors rather than local

factors control local community richness (Cornell and Lawton 1992, Cornell 1999, Oberdorff et

al. 1998), seemed to support this view. However, this approach has been widely criticized (e.g.,

Srivastava 1999, Loreau 2000, Hillebrand and Blenckner 2002, Hillebrand 2005, Shurin and

Srivastava 2005) and it now appears that inferring the absence of strong local interactions and

predominance of regional/historical factors from linear richness relationships was unfounded in

most cases (Loreau 2000, Hillebrand and Blenckner 2002, Hillebrand 2005).

Today, although the debate continues, there is a growing realization that both local and

regional/historical factors are important in determining local community structure (e.g., Palmer

et al. 1996, Loreau 2000, Ricklefs 2000, Mouquet et al. 2003, Cottenie 2005, Harrison and

Cornell 2008, White and Hurlbert 2010), and that their relative importance varies with time,

disturbance regime, the dispersal mode and ability of component species, and other factors

(Palmer et al. 1996, Valone and Hoffman 2002, Mouquet et al. 2003, Van De Meutter et al.

2007).

Hubbell‘s neutral theory (Hubbell 2001) is a more recent contribution to the debate on

what structures local communities, and has stimulated much interest. However, the basic premise

of the theory, mainly that species are ecologically equivalent, does not appear to fit well with

what is known about crayfishes (see Nyström 2002); therefore neutral theory will not be

discussed further. The objective of this chapter is to examine the potential contribution of local,

177

regional, and historical factors to the local community composition of a highly competitive group

of organisms, most of which are poor dispersers – the surface-dwelling crayfishes.

The Combined Influence of Local, Regional, and Historical Factors

In this chapter, I provide evidence in support of the view that a combination of local,

regional, and historical factors are important in determining local (within a single water body or

drainage network) surface-dwelling crayfish community structure. The idea that regional and

historical factors predominate over local factors may stem from the view that local communities

are artificial constructs with little ecological meaning because their boundaries are too small to

encompass the complete distributions of their component species (Ricklefs 2008). For widely

dispersing organisms, this is certainly a valid argument; however, for most surface-dwelling

crayfishes and other aquatic organisms that disperse less readily (those that lack an aerial adult

stage and are poor swimmers) and are therefore largely confined to well defined areas (drainage

networks for running waters and individual water bodies for unconnected standing waters), this

view may be less applicable (see Ricklefs 2004). For these organisms, communities can be

viewed as islands of water among a sea of land (sensu Heino 2011) with well-defined boundaries

(e.g., stream banks, lake shorelines). In these relatively small, more or less closed systems, local

factors may be at least as important as regional and historical factors in determining local

community structure (see Van De Meutter et al. 2007).

178

Local Influences

The interplay of competition with local environmental conditions appears to influence

local community structure in surface-dwelling crayfishes. For example, in Pennsylvania, C. b.

bartonii is often largely restricted to fast-current habitats (e.g., riffles) when in the presence of O.

obscurus or C. (P.) sp. but is more equally distributed among fast- and slow-current habitats

(e.g., pools) when alone (D.A. Lieb, PSU and R.W. Bouchard, ANSP, unpublished data).

Similarly, researchers in West Virginia, New York, and Canada have noted that C. bartonii and

O. obscurus occupy different habitat types when sympatric (Jezerinac et al. 1995, Hamr 1998,

Kuhlmann and Hazelton 2007). In Ohio streams that have been invaded by O. rusticus, resident

O. obscurus occur in headwater areas and O. rusticus in downstream reaches; whereas in streams

that have not been invaded by O. rusticus, O. obscurus occurs throughout the system (Thoma

and Jezerinac 2000). Similarly, Lieb et al. (2011a) speculated that, in Pennsylvania, C. b.

bartonii may be able to persist in the headwaters of streams that have been invaded by O.

rusticus because those areas are not preferred by O. rusticus. More generally, in Pennsylvania, C.

b. bartonii appears to prefer small to midsized streams and is uncommon in larger water ways,

which are often dominated by orconectids (O. obscurus, O. propinquus, O. rusticus ) (Ortmann

1906, Lieb et al. 2011a).

Although additional surveys and experimental work are needed to elucidate the cause of

these patterns, it seems plausible that, in many of these systems, competitive interactions interact

with environmental conditions (habitat type) such that each species is dominant in a different

habitat type and thus able to coexist at the scale of the entire stream but not at the scale of

individual habitats (see similar ideas in Loreau 2000 regarding the coexistence of species in a

mosaic of environmentally variable patches). This suggests that competitive interactions may

179

limit the number of species in a particular habitat type (patch) but that environmental

heterogeneity limits the number of species in the community.

A number of authors have noted that invasions often do not result in the loss of resident

species (e.g., Moore et al. 2001, Sax et al. 2002, Stohlgren et al. 2003, Fridley et al. 2007, Davis

2009, Davis et al. 2011), which has been cited as evidence for a lack of strong local control and

presumed importance of regional and historical factors in structuring local communities

(Ricklefs 1987, Ricklefs 2007, Ricklefs and Jenkins 2011). This view is based on the idea that, in

species saturated communities, structured by local conditions, new species should not be able to

invade without the compensatory loss of resident species (Ricklefs 1987).

Crayfish data from surface waters in Pennsylvania and elsewhere suggest that local

crayfish communities are often saturated and that the addition of exotics frequently results in the

loss of resident species (Schwartz et al. 1963, Berrill 1978, Capelli 1982, St. John 1991, Taylor

and Redmer 1996, Lodge et al. 2000, Wilson et al. 2004, Kuhlmann and Hazelton 2007, Taylor

et al. 2007, Loughman et al. 2009, Loughman and Welsh 2010, Kilian et al. 2010, Swecker et al.

2010, Lieb et al. 2011a, b). In Pennsylvania, replacements can occur rapidly (likely in <10 years)

and interactions between exotic and resident crayfishes can result in injuries to residents (D.A.

Lieb, PSU, personal observations). Thus, it appears that competition, interacting with local

environmental conditions, sets an upper limit to local crayfish species richness in these systems.

At larger scales, invasions have also resulted in the loss of native species (e.g., the

disappearance of O. limosus from much of eastern Pennsylvania, northern Maryland, eastern

West Virginia, and south central New York and other native crayfish from parts of the Midwest,

Canada, and Europe; Holdich 1999, Kuhlmann and Hazelton 2007, Taylor et al. 2007,

Loughman et al. 2009, Loughman and Welsh 2010, Kilian et al. 2010, Swecker et al. 2010, Lieb

180

et al. 2011a, b); however, some of these invaded areas currently harbor more species than they

did prior to invasion (e.g., southeastern Pennsylvania; Lieb et al. 2011a). It is possible that, over

longer time scales as more localities are invaded and species are excluded due to competitive

interactions that the diversity of these areas will decline. It is also possible that crayfish invasions

will end up increasing regional diversity (as was found by Stohlgren et al. 2003) while

decreasing local diversity (via competitive exclusion). This is possible if spatial heterogeneity

allows native crayfish to persist in some habitats that are not favored by exotics (e.g., C. b.

bartonii in the headwaters of drainage networks invaded by O rusticus) or if dispersal rates are

low enough to prevent exotics from colonizing some areas.

To date, most studies of crayfish invasions have taken place in naturally depauperate

areas such as Pennsylvania and nearby states that support a relatively small number of mostly

widespread species. In these areas, invasions would not be expected to immediately result in

range-wide extinction. Instead at short time scales, both natives and exotics would be present

across the landscape resulting in regional enrichment. At longer time scales; however, native

species may be driven to extinction resulting in declines in regional diversity. The effects of

crayfish invasions on more species-rich native faunas that harbor endemic species with much

smaller ranges (e.g., the crayfish fauna of the southeastern United States) are not yet known and

may be more pronounced, potentially resulting in relatively rapid declines in regional crayfish

diversity in those areas (see related ideas in Lodge et al. 2000 and Taylor et al. 2007).

The frequent disappearance of resident species from invaded systems suggests that local

crayfish communities are saturated and strongly influenced by competitive interactions. Across

larger areas (e.g. entire states), crayfish invasions are ongoing and their ultimate effect on

crayfish diversity at that scale is not yet known with certainty.

181

Regional and Historical Influences

Although biotic interactions (mainly competition) appear to limit the number of crayfish

species that can occur in individual communities, regional and historical processes likely

determine potential component species (see similar ideas in Heino et al. 2003, Cottenie and De

Meester 2004, Vellend 2010). For example, because large parts of Pennsylvania were

inhospitable to crayfishes during the last ice age, much of the state is occupied by relatively

recent arrivals that were able to persist in southern Pennsylvania and nearby states during the last

ice age (see Ortmann 1906). Ortmann (1906) even speculated that the range of one of

Pennsylvania‘s crayfish species, Cambarus dubius, may expand in the future due to the natural

colonization of suitable habitats, implying that the colonization process may not be complete for

some of the state‘s crayfishes. The current distributions of many of Pennsylvania‘s crayfish

species can be explained by shifts in drainage patterns related to glacial advances and retreats

(Ortmann 1906), again implicating historic glacial events in determining local community

composition in Pennsylvania. Glacial impacts are not limited to Pennsylvania and have had

substantial effects on crayfish distributions and hence crayfish community structure in other

states such as Illinois, Ohio, and New York (Crocker 1957, Page 1985, Thoma and Jezerinac

2000).

More broadly, the crayfish fauna of much of Pennsylvania and adjacent areas is relatively

young, having only had ~10,000-20,000 years to develop, which has probably contributed to its

depauperate state. In contrast, the crayfish fauna to the south is much older (on the order of

millions to tens of millions of years or more; see Hobbs 1988, Crandall and Buhay 2008) and

much richer. For example, over two-thirds of North America‘s 405 species and subspecies occur

182

in the southeastern United States, many of which are endemic to the region (Taylor 2002, Taylor

et al. 2007). Many of these species appear to have arisen due to the isolating effects of pre- and

post-Pleistocene shifts in river drainages (Crandall and Templeton 1999, Crandall and Buhay

2008). Thus, despite strong local structuring forces (mainly competition) that appear to limit the

number of species that can occur in any single water body or drainage network, unique regional

and historical influences have produced an exceptionally rich crayfish fauna in some parts of

North America. In these species-rich areas, the number of potential component species in any

given community may be larger than in species-poor areas.

Given the strength of competitive interactions and inability of many closely related

(within the same genus) crayfish species to coexist locally, it seems paradoxical that North

America can support such a rich crayfish fauna (400+ species and subspecies). However, this

paradox is reconciled by predictions that at low to intermediate levels of dispersal there is

regional coexistence of strong competitors, whereas when dispersal rates are high local

competitive exclusion extends to the regional scale reducing regional diversity (see Harrison and

Cornell 2008). Applying this concept to crayfishes, it appears that, historically, in Pennsylvania

and elsewhere in North America, strong competitors were able to coexist across the landscape

because low natural dispersal rates prevented them from coming into contact with one another.

In modern times, human introductions have substantially altered this dynamic, resulting in much

higher dispersal rates and, as predicted, competitive exclusion over large areas.

Concluding Remarks

It appears that a combination of local, regional, and historical processes operating across

a variety of temporal and spatial scales have shaped the surface-dwelling crayfish fauna of

183

Pennsylvania and nearby states over the long-term. In more recent times, the human-assisted

spread of exotic species is rapidly changing the crayfish fauna of these areas to an extent not

observed since the end of the last glacial epoch ~10,000 years ago and may eventually result in a

greatly homogenized crayfish fauna. More generally, the preceding discussion provides insights

into how communities of highly competitive, naturally weak dispersers might be assembled and

how they might respond to anthropogenic increases in dispersal rates.

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Sciences 61: 2255-2266.

VITA

David A. Lieb

Education

The Pennsylvania State University, PhD, Ecology 2011

The Pennsylvania State University, MS, Ecology 1998

The Pennsylvania State University, BS, Biology 1991

Selected Technical Reports and Publications

1. Lieb, D.A. and R.F. Carline. 1999. Effects of urban runoff from a detention pond on the macroinvertebrate

community of a headwater stream in central Pennsylvania. Journal of the Pennsylvania Academy of Science 73: 99-

105.

2. Lieb, D.A. and R.F. Carline. 2000. Effects of urban runoff from a detention pond on water quality, temperature,

and caged Gammarus minus (Say) (Amphipoda) in a headwater stream. Hydrobiologia 441: 107-116.

3. Lieb, D.A. and B. Blumberg. 2005. Crayfish Previously Unknown in Pennsylvania Found at Valley Forge. Page

71 in J. Selleck (editor), Natural Resource Year in Review – 2004. Publication D-1609. National Park Service,

Washington D.C.

4. Lieb, D.A., R.F. Carline, and V.M. Mengel. 2007. Crayfish Survey and Discovery of a Member of the Cambarus

acuminatus Complex (Decapoda: Cambaridae) at Valley Forge National Historical Park in Southeastern

Pennsylvania. Technical Report NPS/NER/NRTR—2007/084. National Park Service, Philadelphia, Pennsylvania.

5. Lieb, D.A., R.F. Carline, and H.M. Ingram. 2007. Status of Native and Invasive Crayfish in Ten National Park

Service Properties in Pennsylvania. Technical Report NPS/NER/NRTR—2007/085. National Park Service,

Philadelphia, Pennsylvania.

6. Bouchard, R.W., D.A. Lieb, R.F. Carline, T.R. Nuttall, C.B. Wengert, and J.R. Wallace. 2007. 101 Years of

Change (1906 to 2007). The Distribution of the Crayfishes of Pennsylvania. Part I. Eastern Pennsylvania. Academy

of Natural Sciences of Philadelphia Report No. 07-11. Philadelphia, Pennsylvania.

7. Lieb, D.A., R.F. Carline, J.L. Rosenberger, and V.M. Mengel. 2008. The discovery and ecology of a member of

the Cambarus acuminatus complex (Decapoda: Cambaridae) in Valley Creek, southeastern, Pennsylvania. Journal

of Crustacean Biology 28:439-450.

8. Lieb, D.A. 2010. The biology and management of invasive rusty crayfish in Pennsylvania. Pages 10-11 and 18-

23 in S. Grisé (editor), Conducting an Aquatic Invasive Species Early Response Exercise in Pennsylvania:

Proceedings of a Workshop for Evaluating the Effectiveness of Pennsylvania‘s Rapid Response Plan. Pennsylvania

Sea Grant, Harrisburg, Pennsylvania.

9. Lieb, D.A., R.W. Bouchard, and R.F. Carline. 2011. The crayfish fauna of southeastern Pennsylvania:

distributions, ecology, and changes over the last century. Journal of Crustacean Biology 31: 166-178.

10. Filipová, L., D.A. Lieb, F. Grandjean, and A. Petrusek. 2011. Haplotype variation in the spiny-cheek crayfish

Orconectes limosus: colonization of Europe and genetic diversity of native stocks. Journal of the North American

Benthological Society 30: 871–881.

11. Lieb, D.A., R.W. Bouchard, R.F. Carline, T.R. Nuttall, J.R. Wallace, and C.B. Wengert. 2011. Conservation

and management of crayfishes: lessons from Pennsylvania. Fisheries 36: 489-507.

Professional Positions 1. Invertebrate Zoologist, Western Pennsylvania Conservancy/Pennsylvania Fish & Boat Commission, 2011-present

2. Graduate Assistant (PhD) and Researcher, The Pennsylvania State University, 2003-2011

3. Staff Scientist, Stroud Water Research Center, 1997-2003

4. Graduate Assistant (MS), The Pennsylvania State University, 1994-1997

5. Staff Scientist, Academy of Natural Sciences of Philadelphia, 1992-1994

6. Research Technician, The Pennsylvania Fish and Wildlife Cooperative Research Unit, 1991-1992

7. Research Technician, The Pennsylvania Fish and Boat Commission, summer 1990

8. Research Technician, The Pennsylvania Fish and Wildlife Cooperative Research Unit, summer 1989

the ecology, distribution, conservation, and …

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