Esox lucius: Northern pike

Shannon Hennessey

FISH 423 Aquatic Invasion Ecology

Fall, 2011

Diagnostic information

Scientific name

Order: Esociformes

Family: Esocidae

Genus: Esox

Species: E. lucius

Common names: Northern pike, pike,

jackfish, grand brochet

Basic identification key

The Northern pike Esox lucius can

be characterized by a long body with a ‘duck

bill’ snout, a large mouth with many sharp teeth,

and cheeks that are completely scaled. The

dorsal and anal fins are set posteriorly on the

body with a narrow caudal peduncle and a

mildly forked caudal fin. E. lucius have greenish

dorsal and lateral surfaces with yellow bars or

rows of spots running along the sides, and a

whitish ventral surface (Figure 1). Body lengths

range from 46-51 cm on average, with an

average weight of 1.40 kg (Morrow 1980).

However, in the United States these fish can

grow to sizes up to 1.5 m long with weights up

to 35 kg.

Life history and basic ecology

Life cycle

Esox lucius has a relatively simple life

cycle, in which they have 4 life stages as defined

by Inskip (1982), all of which have specific

habitat requirements. The embryo stage is when

the fish has not yet emerged from the egg.

Immediately after hatching, these become fry

until they assume adult proportions at a size of

approximately 6.5 cm (Franklin and Smith

1960). Juveniles are defined as those fish from

6.5 cm in length to the onset of sexual maturity,

or the stage at which their gonads begin to

develop. Once these fish have reached sexual

maturity, they become adults until the end of

their life cycle. These fish are typically solitary

and highly aggressive (Craig 2008).

Spawning occurs during the spring flood soon

after ice-out, when water temperatures are 8-

12°C and can last from a few days to more than

a month (Franklin and Smith 1963, Inskip 1982,

Casselman and Lewis 1996). E. lucius migrate

up tributaries and spawns in calm, shallow

waters of wetlands or flooded marshes where

there are mats of submerged vegetation. This

Figure 1: Northern pike Esox lucius color image (top) and black

and white image with diagnostic information (bottom) (Montana

State Government’s Field Guide).

vegetation is essential not only to the survival of

the eggs, but will also become important nursery

habitat once the juveniles have emerged

(Casselman and Lewis 1996, Mingelbier et al.

2008). Eggs are deposited where they then stick

to the vegetation mats, which suspend them off

of the potentially anoxic sediments until

hatching approximately two weeks later

(Franklin and Smith 1963, Casselman and Lewis

1996). Water level is a very important factor in

embryo survival, due to the fact that E. lucius

usually spawn in water as shallow as 0.1 – 0.2 m

deep (Inskip 1982). High water levels during

spawning can also be associated with larger

juveniles as the high waters bring an influx of

nutrients, increasing the productivity in areas

where larval fish are growing (Johnson 1957,

Casselman and Lewis 1996).

Once the eggs hatch, young-of-the-year fish

remain among the submerged vegetation, which

provides important nursery habitat. At hatching,

these fish are 7-9 mm in length on average

(Frost and Kipling 1967, Forney 1968, Inskip

1982). During the first few days, fry remain

attached to the vegetation until their yolk sac

was absorbed (Frost and Kipling 1967, Inskip

1982). The juveniles grow rapidly, increasing

their size and activity, and the shelter provided

by the vegetative cover helps enhance survival

(Casselman and Lewis 1996). As they grow,

juveniles move to more floating and submergent

vegetation, rather than the emergent vegetation

preferred by fry, but remain in shallow waters

(Casselman and Lewis 1996, Craig 2008).

Maturation is highly dependent on growth rate,

with males typically maturing at 34-42 cm total

length and females at 40-48 cm (Frost and

Kipling 1967; Priegel and Khron 1975). In the

US, both males and females typically mature at

about 2 years of age, although there is variation

due to differential growing conditions (Inskip

1982). E. lucius can live as long as 24 years, but

longevity is also strongly correlated with growth

rate (Miller and Kennedy 1948). At the more

southern end of their distribution, these fish may

only live up to 4 years. (Buss and Miller 1961,

Schryer et al. 1971, Inskip 1982). Adults are

also strongly associated with vegetation and

shallow waters, showing a preference for

submergent vegetation as it facilitates optimum

foraging efficiency (Casselman and Lewis 1996,

Craig 2008).

Feeding habits

E. lucius is characterized as a keystone

piscivore that can shape the composition,

abundance and distribution of fish communities

(Craig 2008). They are visual predators that are

primarily active during the day, feeding on a

wide variety of prey from invertebrates to fishes

(Polyak 1957, Carlander and Cleary 1949,

Casselman and Lewis 1996, Craig 2008). As

opportunistic feeders E. lucius will feed on prey

that is seasonally abundant, although the size of

their prey is limited by both their size and the

size of their prey (Craig 2008). They can

consume a wide range of prey sizes, but have

also been shown to be size-selective predators

(Nilsson and Bronmark 2000, Craig 2008).

Although they can be cannibalistic, this has not

been shown to comprise a large portion of their

diet (Frost 1954, Lawler 1965, Mann 1976).

Aquatic vegetation is particularly important for

feeding as these fish utilize and ‘ambush’ style

of predation (Inskip 1982, Casselman and Lewis

1996). Intermediate vegetation densities have

been associated with optimum predation

efficiency (Craig and Black 1986), and calm,

clear waters provide better visibility associated

with more efficient prey capture (Craig 2008).

Fry begin feeding once they reach a length of

approximately 10-12 mm in length, about 10

days after hatching (Franklin and Smith 1963).

They initially feed on zooplankton, but soon

begin to feed on aquatic insect larvae and fish,

marking the start of piscivory very early in their

life (Hunt and Carbine 1951, Frost 1954, Inskip

1982). Within 4-5 weeks after hatching, at a

length of approximately 50-60 mm, their diet is

comprised mostly of fish, and fry as small as 21

mm have been shown to be cannibalistic (Hunt

and Carbine 1951). As they continue to grow,

their prey is predominantly fish, although they

have been known to prey on crayfish, waterfowl

and even small mammals (Frost 1954, Lagler

1956, Seaburg and Moyle 1964, Lawler 1965,

Mann 1976, Inskip 1982).

Reproductive strategies

E. lucius is an iteroparous species,

undergoing multiple reproductive events, with a

relatively high fecundity. These fish form

spawning groups, usually consisting of one

female and either one or several males. 5-60

eggs are released at any one spot, where they are

then fertilized by males (Svardson 1949, Clark

1950). The gametes are broadcasted, with no

parental care provided post-spawning (Eddy and

Underhill 1974, Inskip 1982). Any one

spawning group can release gametes over a large

area of spawning habitat (Koshinsky 1979).

Franklin and Smith (1963) found the number of

eggs produced to be highly dependent on female

body size, described by the equation y = 4401.4x

– 66245, with y equal to the number of eggs

produced, and x as the total length of the fish in

inches. Females weighing 0.75 lbs may produce

from 9,000 to 10,000 eggs, while a female

weighing 10 lbs may produce 100,000 eggs

(Lagler 1956).

Environmental optima and tolerances

Northern pike are a cool water species,

but have a wide range of environmental

tolerances including water temperature,

dissolved oxygen concentration, and water

clarity, which, in part, can be attributed to their

success as an invasive species (Casselman 1978,

Steinberg 1992, Casselman and Lewis 1996).

These optima and tolerances, however, vary

among life-cycle stages (Inskip 1982).

E. lucius embryos are tolerant of temperatures

up to 19°C (Siefert et al. 1973), with maximum

hatching success occurring at temperatures from

9-15°C and severe mortality at temperatures

near 5°C (Hassler 1970). Dissolved oxygen

concentrations of 4.5 mg/L is optimal for

embryo development, while concentrations of

3.2 mg/L or less result in high embryo mortality

(Siefert et al. 1973). Embryos are particularly

sensitive to high rates of siltation (≥1 mm/day)

(Hassler 1970), and exposure to hydrogen

sulfide of concentrations greater than 0.014-

0.018 ppm for 96 hours decreases hatching

success (Adelman and Smith 1970a).

Fry survival and growth is greatest at

temperatures from 18.0-20.8°C, with poor

survival at temperatures lower than 5.8°C and

higher than 25.6°C (Lillelund 1966, Hokanson et

al. 1973). Hydrogen sulfide concentrations

greater than 0.004-0.006 ppm for 96 hours

significantly decreased survival of yolk sac fro

(Adelman and Smith 1970a).

Juvenile E. lucius reach maximum growth rates

at temperatures ranging from 19-21°C, with

significantly decreased survival at temperatures

lower than 3°C and above 28°C (Casselman

1978). Growth rates were hindered at dissolved

oxygen concentrations below 7 ppm, and very

low juvenile survival occurred at concentrations

below 3 ppm (Adelman and Smith 1970b).

Feeding ceased at less than 2 ppm and no fish at

dissolved oxygen concentrations of 1 ppm

survived more than 20 hours in a study by Petit

(1973).

Adults have the greatest environmental

tolerances of the life-cycle stages, with a

maximum temperature tolerance of over 30°C

(Ridenhour 1957). Optimum growth occurs at

approximately 20-21°C, but adult E. lucius have

shown no apparent stress at temperatures as low

as 0.1°C prior to freezing in a shallow lake

(Casselman 1978). Despite these wide

temperature tolerances, sudden drops in

temperature can be lethal (Ash et al. 1974,

Inskip 1982). A significant decrease in feeding

has been observed in adults exposed to dissolved

oxygen concentrations around 2-3 mg/L, and

feeding has been shown to stop altogether at

concentrations less than 2 mg/L (Adelman and

Smith 1970b, Casselman and Lewis 1996). E.

lucius can inhabit areas with pHs ranging from

6.1-8.6 (Margenau et al. 1998), and can tolerate

some salinity, having been found frequently in

the Baltic Sea (Crossman 1979).

Biotic associations

Biotic associations of E. lucius vary

across the native and introduced range of the

species, although there are numerous pathogens

and parasites that can be associated with this

species. One notable ectocommensal organism

associated with E. lucius is the ciliate

Capriniana piscium, also known as Trichophyra

piscium. C. piscium attaches to the lamellar

epithelia of the gill surface of E. lucius using

microfobrils that connect to the host cell

membrane (Lom 1971, Hofer et al. 2005; Figure

2). It was previously thought that high densities

of these organisms could cause tissue damage in

the host, however, there is no evidence of C.

piscium feeding on the host cells (Lom and

Dykova 1992). Instead, this commensal uses its

tentacles to feed on ciliates that are in the water

that passes through the fish gill lamellae (Lom

1971, Dovgal 2002, Hofer et al. 2005).

Current geographic distribution

Distribution in the United States

and the PNW

In the United States, the native

range of Esox lucius includes the

Great Lakes and Mississippi

River basins as well as Alaska,

Pennsylvania, Missouri and

Nebraska (Page and Burr 1991),

and the South Saskatchewan

River Drainage in Montana

(Holton and Johnson 1996).

However, E. lucius has been

reported to have non-native

populations in 41 states, including Washington,

Oregon and Idaho (Figures 3 and 4).

In the Pacific Northwest, E. lucius has an

established population in Coeur d'Alene Lake,

Idaho, and has been reported to have established

populations in the Spokane River in both Idaho

and Washington, as well as Lake Pend Oreille,

Idaho, and the Pend Oreille River in Washington

and Idaho. There have also been general reports

of the presence of established E. lucius

populations in the Columbia River in Oregon as

well as Washington (Fuller 2011) (Figure 4).

History of invasiveness

Esox lucius has a long history of

introduction and subsequent invasions, both in

the United States and elsewhere. This species is

historically absent from Mediterranean France,

Figure 2: C. piscium in the interlamellar space of fish

gills. The tentacles protrude from the gill surface where

they can capture prey (Hofer et al. 2005).

Figure 3: Native and invaded ranges of E. lucius in the United States (US

Geological Survey 2011).

central Italy, southern and western Greece, and

northern Scotland, but has been widely

translocated throughout Europe (Kottelat and

Freyhof 2007), introduced to Spain, Portugal,

and Ireland (Welcomme 1988), among other

locations. E. lucius has also been introduced to

Algeria, Ethiopia, Madagascar, Morocco,

Tunisia, and Uganda (Welcomme 1988, Lever

1996).

As an important game fish, the introduction

history of E. lucius outside of its native range in

the United States dates back to the 1800’s. The

first recorded introduction of Esox lucius in the

United States outside of its native range was in

the 1840’s when the United States Fish

Commission intentionally introduced the fish

into the Hudson River Basin, where it

subsequently spread to the lower Hudson River

by 1976 (Mills et al. 1997). Widespread

stocking of E. lucius in the Chesapeake Basin

began in the 1960’s in Pennsylvania, followed

by stocking in Maryland and Virginia

(Denoncourt et al. 1975). In 1992, 4000 E.

lucius fingerlings were released in the District of

Columbia, although the survival of these fishes

is unknown (Christmas et al. 2000). In

Colorado, E. lucius was introduced to the Elk-

head Reservoir of the Yampa River drainage in

1977, where they subsequently invaded the

Green River basin of Colorado and Utah in 1981

(Wick et al. 1985), with similar introduction

histories for other states with established E.

lucius populations.

Figure 4: Native and invaded range of E. lucius in the Pacific Northwest with general ranges as well as point

occurrences of populations (Adapted from the US Geological Survey 2011).

E. lucius was first introduced to the Pacific

Northwest in the early 1950’s (Brown 1971) and

now occurs throughout the Columbia River

basin. It was illegally stocked into Coeur

d'Alene Lake, Idaho, in the early 1970’s (Rich

1993), where it then spread into several other

lowland lakes in northern Idaho (McMahon and

Bennett 1996). Although E. lucius is native to

Montana in the Saskatchewan River drainage, it

has now spread throughout the state (DosSantos

1991), and has also spread to Idaho, Washington

and Oregon.

Invasion process

Pathways, vectors and routes of introduction

The primary introduction pathway of Esox

lucius is the intentional stocking of the fish for

recreational purposes (Fuller 2011). As an

important sport fish, E. lucius has been

intentionally introduced across the country

initially by the United States Fish Commission,

and later by various state agencies, to stimulate

fishing opportunities in various parts of the

country (Jenkins and Burkhead 1993; Scott and

Crossman 1973). Intentional introductions still

occur due to public pressures for fishing

opportunities, despite the risks associated with

introductions (McMahon and Bennett 1996).

Illegal stocking, or bait-bucket transfer, also

frequently occurs, in which E. lucius are

intentionally introduced to an ecosystem without

authorization. This is typically done to promote

fishing opportunities in the recipient ecosystem

for those stocking the water body, but this

unregulated introduction of E. lucius can play a

large role in facilitating the spread of this

species (McMahon and Bennett 1996).

In the Pacific Northwest, one of the initial

introductions of E. lucius was via illegal

stocking with Coeur d’Alene Lake, Idaho (Rich

1993), resulting in the subsequent spread of this

species across northern Idaho. E. lucius

populations in Washington are a result of illegal

stocking in the Flathead, Bitterroot and Clark

Fork River systems in Montana. These fish then

migrated into Lake Pend Orielle, through Idaho

by way of the Pend Orielle River, into

Washington (Washington Department of Fish

and Wildlife). In the past few years, these fish

have spread from Boundary Reservoir into the

Columbia River, and can now be found in

Oregon as well, most likely though downstream

migration in the Columbia River (McMahon and

Bennett 1996).

Factors influencing establishment and spread

The establishment and spread of a species

is determined by the environmental tolerances of

that species, as well as certain life-history

characteristics. E. lucius can withstand a wide

range of environmental conditions (Casselman

1978, Steinberg 1992, Casselman and Lewis

1996), increasing the likelihood of establishment

and spread of this species due to the fact that

there is a large amount of habitat with tolerable

environmental conditions available. E. lucius is

also a relatively fecund species (Casselman and

Lewis 1996), which may allow for rapid

establishment of populations and subsequent

spread to new areas.

The main factor that may restrict the ability of E.

lucius to establish and spread, however, is the

availability of shallow habitat with submerged

vegetation (DosSantos 1991) vital in spawning

as well as adult foraging, as well as the presence

of suitable fluctuation of water levels during the

spawning period (see life-cycle section) (Inskip

1982). The nature of these specialized habitat

requirements therefore serve to limit the

distribution and likelihood of spread (Jones

1990). Because these fish are highly predatory,

an abundant prey base in the recipient

community is also necessary to support E. lucius

populations (McMahon and Bennett 1996),

which may further constrain the amount of

suitable habitat available for colonization.

Potential ecological and/or economic impacts

There are many potential ecological and

economic impacts associated with the

introduction of E. lucius outside of its native

range. As a keystone piscivore, this fish can

shape the composition, abundance and

distribution of fish communities (Craig 2008),

which has important implications when

considering the native fish communities, as well

as sport fisheries. In places where E. lucius is

overpopulated, there is a resultant overfeeding

on their prey base, which impedes the growth of

these fish. Stunted growth, however, does not

result in lower reproduction, so overabundant E.

lucius populations can not only severely

decrease prey fish abundances (He and Kitchell

1990), but also create undesirable fisheries due

to their small size. If E. lucius populations were

left unchecked, they could cause a loss of

revenue from sport fisheries as well as have

drastic impacts on native fish populations

(Washington Department of Fish and Wildlife).

The effects that E. lucius can have on native

fishes have very important implications,

especially when considering the native fishes of

the Pacific Northwest. One of the main concerns

associated with the spread of E. lucius is the

impact this species can have on local salmon

populations (McMahon and Bennett 1996). E.

lucius have been shown to have drastic negative

impacts on salmon populations as they feed on

salmon smolts migrating to sea (Larson 1985,

Petrvozvanskiy et al. 1988) and these fish have

been associated with the extinction of local

salmonid populations (Bystrom et al. 2007,

Spens 2007, Spens and Ball 2008), making their

invasion a serious threat.

While the introduction of E. lucius threatens to

cause serious declines in a popular Pacific

Northwest sport fish, E. lucius in itself is also an

important sport fish, and there are strong

economic benefits associated with the

introduction of this species. Stocking of these

fish can generate popular sport fisheries, which

can create important revenue that enhances local

economies (McMahon and Bennett 1996).

However, this economic benefit can to lead to an

increase in the frequency of illegal stocking

(Vashro 1990, 1995), further contributing to the

continued spread of E. lucius and the harmful

effects that can follow.

Management strategies and control methods

There are several different management

strategies and control methods for Esox lucius

populations, the most effective of which,

however, is prevention. Once established, these

fish can spread to neighboring habitats,

drastically affecting the recipient biotic

communities (He and Kitchell 1990, Craig

2008), making a preemptive response the best

approach. One of the main prevention strategies

is education, allowing for an early-warning

system for new introductions in which a quick

response can be enacted, as well as increasing

awareness of the impacts of E. lucius, hopefully

deterring the intentional introduction of the

species.

However, in the cases where introduction has

already occurred, primary strategies for the

control of E. lucius include the suppression of E.

lucius populations, the prevention of spread to

other waterways, and removal of as many

organisms as possible using a variety of

methods. Prevention of spread to other

waterways is particularly important in

attempting to control E. lucius populations,

because by limiting their access to habitat it

constrains their ability to spread and establish

subsequent populations. Electrofishing, trapping

and the use of rotenone, a fish toxicant, are

common strategies for fish population

suppression and removal, although they tend to

be costly and/or labor intensive, with tradeoffs

associated with each strategy (CDF&G et al.

2006).

An important management strategy in

preventing the spread of E. lucius is regulation

of illegal introductions. Many states have laws

that prevent the transport of live fish from a

waterbody (e.g., Idaho, Oregon, and western

Montana), but there is strong opposition from

the public and it is difficult to closely manage

the actions of individuals stocking fish illegally

(McMahon and Bennett 1996). In Montana, the

legislature stiffened penalties associated with the

illegal stocking of fish, such as fines, suspension

of fishing privileges, and liability for cost of

restoring a fishery, and they have even offered

rewards for reporting such activity (McMahon

and Bennett 1996). Following the actions of the

Montana legislature in creating public incentive

seems to be a good place to start in terms of

finding better ways to raise awareness and

prevent the introduction of invasive species.

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Other key sources of information and bibliog

raphies

California Department of Fish and Game

http://www.dfg.ca.gov/lakedavis/biology.html

FishBase

http://www.fishbase.org/summary/Esox-

lucius.html

USGS Nonindigenous Aquatic Species

Database. Pam Fuller. 2011. Esox lucius.

http://nas.er.usgs.gov/queries/FactSheet.aspx?Sp

eciesID=676 Revision Date: 6/21/2010

Washington Department of Fish and Wildife

http://wdfw.wa.gov/ais/esox_lucius/

Expert contact information in PNW

David H. Bennett

Fish and Wildlife Resources Department

University of Idaho, Moscow, ID 83844-1136

dbennett@uidaho.edu

Thomas E. McMahon

Biology Department, Fish and Wildlife Program

Montana State University, Bozeman, MT 59717-

0346

ubitm@msu.oscs.montana.edu

Deane Osterman

Executive Director for Natural Resources

Kalispel Tribe

Kalispel Tribal Headquarters

P.O. Box 39

Usk, WA 99180

Phone: (509) 445-1147

Fax: (509) 445-1705

Current research and management efforts

Currently, there are numerous ongoing

efforts to control the spread of Esox lucius, with

a focus on eradicating populations that have

been introduced illegally. In Montana, E. lucius

removal programs have been implemented in the

Milltown Dam Reservoir to help restore native

cutthroat and bull trout. The dam impedes

salmonid migration causing them to concentrate

in the reservoirs, providing easy prey for the E.

lucius that reside there (Dickson 2003). The

Montana Department of Fish, Wildlife, and

Parks have temporarily lowered the later levels

of the reservoir each year to kill yearling E.

lucius that occupy the back channels, resulting

in reduced fish populations, although the process

is labor intensive. Montana has also recruited

angler organizations to help control E. lucius

populations, as well as prevent illegal

introductions (McMahon and Bennett 1996).

The California Department of Fish and Game

(CDF&G) has been treating a lake with an E.

lucius population with rotenone, a common fish

toxicant, in an attempt to eradicate the fish. The

first time this was done, E. lucius were found

two years later, so another eradication attempt is

planning to be undertaken (CDF&G et al. 2006).

Experimental control measures such as the use

of net barriers, electrofishing, and encircling

nets are also being used to control E. lucius

populations, as well as the blockage of spawning

areas, reducing food availability, increasing

public awareness and implementing a

comprehensive fish monitoring program.

In Washington, management efforts are being

directed towards minimizing the impacts of E.

lucius on native fish species and reducing E.

lucius abundances in the Box Canyon Reservoir.

The Washington Department of Fish and

Wildlife (WDFW) is working with the Kalispel

Tribe Natural Resources Department (KNRD) to

devise an appropriate management strategy for

the Pend Orielle River. Surveys are being

conducted to determine the relative abundances

of E. lucius, the structure of the overall fish

community, and the timing of E. lucius

spawning activities. The WDFW is attempting to

learn more about the impacts of E. lucius on

native salmonid populations, using events that

occurred in south-central Alaskan watersheds as

a model to attempt to prevent similar damage to

Washington salmonid populations, and has

proposed to remove E. lucius’s classification as

a game fish, causing it to be listed solely as a

prohibited species.