-9 '

CREEL SURVEY FOR THE

WEST BRANCH OF THE PENOBSCOT RIVER

ChemRisk® A Division of McLaren/Hart

Stroudwater Crossing 1685 Congress Street

Portland, Maine 04102 (207) 774-0012

November 22, 1991

CO oz V) oo

oOofihemRisk NJ

A Division of McLaren/Hart Environmental Engineering

ChemRisk A Division of McLaren/Hart Environmental Engineering

CREEL SURVEY FOR THE

WEST BRANCH OF THE PENOBSCOT RIVER

prepared by:

ChemRisk® Division of McLaren/Hart

Stroudwater Crossing 1685 Congress Street

Portland, Maine 04102 (207)774-0012

Reviewed and Approved By:

Ellen S. Ebert Date Project Manager

CREEL SURVEY FOR THE WEST BRANCH OF THE PENOBSCOT R I V E R

Table of Contents

1.0 Introduction 1

2.0 Data Collection and Analysis 3

2.1 Selection of Study Areas 3 2.2 Survey Development and Data Collection 3 2.3 Data Analysis 5

3.0 Results 8

4.0 Discussion 10

5.0 References 13

APPENDIX A: Interpretation of Notched Box Plots A-l

APPENDIX B: Uncertainty Analysis B-l

CREEL S U R V E Y FOR THE WEST BRANCH OF THE PENOBSCOT RIVER

List of Figures

Figure 1. General Creel Census Form 3a

Figure 2. Fish Consumption Survey Form 3b

Figure 3. West Branch Penobscot Study Areas 4a

Figure 4. Notched Box Plots for Fish Consumption by Fishing Location 9a

APPENDIX A:

Figure A-l. Notched Box Plot Diagram A-la

CREEL S U R V E Y FOR THE WEST BRANCH OF THE PENOBSCOT R I V E R

List of Tables

Table 1. Fish Harvest by Interviewed Resident Anglers 6a

Table 2. Analysis of Fish Consumption Rates for Consuming Anglers on the West Branch 8a

APPENDIX B:

Table B-l. Monthly Distribution of Interviews in Consumption Survey B-la

Table B-2. Distribution of Angler Participation and Harvest by Month B-2a

Table B-3. Distribution of Calculated Minimum Fish Consumption Rates B-4a

Table B-4. Distribution of Frequency of Fishing Trips Reported in Consumption Survey B-4b

Table B-5. Distribution of Angler Participation by Month B-4c

Table B-6. Distribution of Fish Creeled and Intended for Consumption by Interviewed Anglers B-5a

Table B-7. Distribution of Fish Creeled per Angler by Month and Adjustment Factors B-5b

Table B-8. Comparison of Monte Carlo Simulation Results with Original Consumption Rate Estimates B-7a

CREEL SURVEY FOR THE WEST BRANCH OF THE PENOBSCOT RIVER

1.0 Introduction

The Maine Department of Environmental Protection is proposing to establish a water quality

standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in ambient waters of the state. Due to

the physical and chemical properties of TCDD that influence its environmental fate and transport,

the consumption of fish is the primary route of human exposure to TCDD found in aquatic

environments. Therefore, the estimation of a representative rate offish consumption is critical to

the derivation of a scientifically based and health-protective water quality standard for TCDD in the

State of Maine.

Published studies that specifically investigate or estimate freshwater fish consumption in Maine are

nonexistent. The fish consumption data that are available in the scientific literature are based on

information gathered from other regions of the country (Humphrey, 1976; Fiore et al., 1989;

Turcotte, 1986; Honstead et al., 1971) where fishing patterns are different, waters are more fertile,

and species composition is either different or more diverse than in Maine rivers. Because

differences in the availabilities of desirable species, fishing habits, fishing regulations, regional

climate, and cultural heritage all influence the amount of freshwater fish that is consumed by

anglers in a particular region of the country, the applicability of data from other regions to the

consumption habits of Maine residents is of limited value and questionable validity. Availability of

target species, like salmon and trout, is likely to be lower in Maine rivers than in larger freshwater

systems in other regions of the country. Bag limits for target species, designed to preserve

fisheries resources, further limit the amount of fish that can be creeled by individual anglers. In

addition, many of the more available fish, like bass, perch, and pickerel, that are resident in

downriver reaches of Maine's larger rivers, are less desirable as food fish.

According to the Maine Department of Inland Fisheries and Wildlife (MeEFW), freshwater fish

species are not locally harvested and commercially marketed in Maine (MelFW, Personal

Communication, 1990). Consequently, the only dietary source of local freshwater fish is through

recreational fishing. Only those individuals who fish or who share in the catch of other anglers are

able to consume freshwater fish from Maine's waters.

Although Maine has more than 200,000 licensed resident anglers, no extensive study has been

conducted on the consumption habits of those individuals. MelFW has monitored angler use and

catch on many of the State's lakes and ponds but few of its rivers. Consequently, any significant

information on the catch of river anglers is limited and consumption data are unavailable.

During the Spring of 1990, three studies were initiated in an effort to characterize fish consumption

by resident Maine anglers: a mail survey, designed to collect information from a representative

sample of Maine's resident angling population, and two site-specific creel surveys, designed to

gather data from anglers fishing on individual rivers in Maine. The purpose of these studies was to

collect sufficient data to allow the characterization of fish consumption rates for representative

waterways and for the State as a whole, thereby providing a sound basis for the development of

health-protective water quality standards for Maine.

This report summarizes the results of the creel survey conducted on the West Branch of the

Penobscot River (West Branch). The results of the statewide mail survey and the creel survey

conducted on the Saco River are presented in two separate reports (ChemRisk, 1991a,b).

2.0 Data Collection and Analysis

2 .1 Selection of Study Areas

In selecting rivers for the creel surveys, a question was raised as to the effect that fish consumption

advisories issued on several major rivers in the State might have on angler effort or consumption

rates. To deal with this issue, river reaches for which no fish consumption advisories have been

issued were selected as study areas. These were the Saco River in southern Maine (ChemRisk,

1991b) and the West Branch of the Penobscot River (West Branch) in north-central Maine.

Selection of these two rivers provided both geographical and fish species diversity. In addition,

the two study areas represent diversity in angler population density; the Saco River is located in the

most densely populated region of the State while the West Branch is located in an area of the State

that has a low population density (MelFW, 1990). Despite these differences, both rivers were

expected to have high use by recreational anglers as the Saco River has brown trout and bass

fisheries easily accessed by anglers living in the southern part of the state, and the West Branch is a

target destination for many anglers due to its world-famous landlocked salmon fishery.

2.2 Survey Development and Data Collection

Great Northern Paper has conducted yearly creel surveys for the fisheries of the West Branch since

1977 as part of its ongoing fisheries monitoring program. The questionnaire that has been

traditionally used in conducting angler interviews (Figure 1) was designed to collect data on angler

effort, catch, and the portion of the catch that is creeled. A review of this survey form indicated

that there was a need for supplemental questions that would specifically address the issue of fish consumption. With the assistance of Edward Spear, the fisheries biologist who supervised and

conducted the Great Northern Paper creel surveys, additional questions were designed (Figure 2).

These questions asked anglers how often they went fishing on the West Branch, whether they

intended to consume the fish they had creeled, who would share in the catch, how that fish was to

be prepared, and which parts of the fish would be consumed. These supplemental questions were

asked only when survey clerks interviewed anglers who had creeled fish. The survey clerk

weighed and measured each creeled fish and recorded the information by species. All data were

collected on an individual fish basis to account for the differences in sizes and variations in

preparation method that might occur among species.

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The fish consumption portion of the survey was added to the ongoing survey being conducted by

Great Northern. It was begun on May 26, 1990 and continued through September 30, 1990, the

last day of the open water fishing season. Fisheries management data was collected

simultaneously, and although these data were not used to estimate consumption rates, they were

helpful in defining the uncertainty associated with the consumption rate estimates (Appendix B).

The West Branch was divided into two main study areas for the purpose of this survey (Figure 3).

Section A is a pristine area in which landlocked salmon provide the principal fishery. Section B,

located downstream of the Millinocket Impoundment (i.e., Quakish Lake), is a developed area that

provides bass, perch and pickerel fisheries, with salmon providing only a seasonal fishery.

Both Sections A and B of the West Branch contain lacustrine areas and/or hydroelectric facilities

that create boundaries and thus define sections, or reaches, of the river. These different reaches

support different types of fisheries. Within the two main study areas, the following reaches of the

West Branch were surveyed:

Section A

1. Ripogenus Dam to Abol Bridge

2. North Twin Dam tailwater (to Quakish Lake)

Section B

3. Millinocket Mill tailwater to Shad Pond

4. Shad Pond Falls to Dolby Dam (Dolby Impoundment)

5. Dolby Dam tailwater

While the number of survey days per week varied during the season, a minimum of three days per

week were spent surveying the river, with one day falling on a weekend or holiday. Although the

length of the survey day varied with the reach of river being surveyed, seven hours was the

minimum length of a survey day. On survey days, all observed anglers were counted and, when

possible, interviewed. When two or more anglers were fishing together, data were collected from

a party spokesperson.

Due to the topography, access is limited for the river reach between the Millinocket and Dolby

Impoundments. This, coupled with the large number of boat anglers, limited interviews by the

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survey clerk along this reach. Therefore, in addition to the interviews conducted on this reach,

flights were used to collect information about angler use of the reach. Flight clerks recorded the

number of anglers fishing the reach at a given time, yielding instantaneous angler counts.

2.3 Data Analysis

Fish consumption rates were estimated for each individual angler interviewed to yield a distribution

of fish consumption rates. Each consumption estimate reflects the average daily consumption rate

for the angler and for all of the fish-consuming individuals with whom the angler shares his or her

catch. Separate fish consumption distributions were generated for the following populations: all

consuming anglers interviewed, all consuming anglers on Section A, and all consuming anglers on

Section B. The distributions of fish consumption rates for West Branch Sections A and B are

subsets of the distribution for the combined total for all reaches within the study area. The

calculation of an average daily fish consumption rate was completed for each angler using the

following equation:

d = Wi x P x I/Hi x Ti x L x 1/D

Where:

Cj = Average consumption rate for persons consuming catch of angler i (g/person-day)

Wj = Total weight of fish caught and creeled by angler i (g whole fish/trip)

P = Edible portion (g edible/g whole fish)

HI = Number of persons who share angler i's catch (persons)

T, = Angler i's average number of fishing trips per week (trips/week)

L = Length of fishing season (26 weeks/year)

D = Total days per year (365 days/year)

If fish were creeled, but were to be given away, they were not included in the calculation of the

consumption rate for the anglers.

Survey clerks recorded the weight of whole or field-dressed fish creeled by the angler at the time of

the interview. To account for those portions of a whole fish that arc not generally consumed, it

was necessary to determine the edible portion relative to whole fish weight for the species

harvested from the West Branch. Edible portion estimates were determined for landlocked salmon

and smallmouth bass (Ebert, 1991). Edible portion for white perch was determined using data

collected as part of Great Northern's ongoing fisheries work. Together these three species

represented 95 percent of the total fish weight consumed by the anglers interviewed (Table 1).

To determine the edible portion of West Branch landlocked salmon, 12 landlocked salmon, ranging

in size from 398 to 1,174 g (14 to 41 oz.), were collected from the West Branch (Ebert, 1991).

Fish lengths ranged from 371 to 477 mm (15 to 19 in.). The whole body weight of each of the

fish collected was recorded. The fish was then field dressed and reweighed to determine the

weight of the viscera. Finally, the fish was filleted and the fillet weight was recorded. The

average edible fraction for landlocked salmon was 37 percent. The 90 percent upper confidence

limit of 39 percent was used in this analysis as the edible portion for landlocked salmon.

To calculate the total body weight of field-dressed salmon, a species-specific linear equation

relating dressed weight to whole weight was used. This equation was derived using data from

field samples of landlocked salmon collected from the West Branch (Ebert, 1991). The edible

portion was then applied to this estimated whole weight to calculate the consumed weight.

A similar method was used to determine the edible portion of smallmouth bass. Eleven

smallmouth bass, ranging in size from 356 to 613 g (13 to 22 oz.), were collected from the West

Branch (Ebert, 1991). Fish lengths ranged from 308 to 360 mm (12 to 14 in.). The whole body

weight and fillet weight of each of the fish collected were recorded. The edible portion ratio was

then calculated by averaging the percent of edible fish from all of the individual fish. For

smallmouth bass, the average edible portion was 29 percent. The 90 percent upper confidence

limit of 31 percent was used for this analysis as the edible portion for smallmouth bass.

The edible portion of white perch was estimated from field data collected from the Dolby

Impoundment in March 1990 by Great Northern as part of their ongoing fisheries work. Nineteen

white perch, ranging in length from 183 to 288 mm (7 to 11 in.), were collected. Their full body

weights ranged from 50 to 400 g (2 to 14 oz.). After weighing, the fish were filleted and

reweighed and the fillet weights were recorded. These fillet weights were then compared to the

whole body weights to determine the edible portion of each fish. The average edible portion ratio

was then derived from the edible portion ratios calculated for each individual fish. For white

Table 1. Fish Harvest by Interviewed Resident Anglers8

Weight Number Number Consumed

Species Creeled Consumed (kg)

White Perch 103 86 30.4

Landlocked Salmon 39 37 30.8

Smallmouth bass 29 27 12.0

Pickerel 4 4 3.39

Brook trout 2 2 0.45

a. Based on single interviews and the fish creeled at the time of the interview.

6a

perch, the average edible portion was 24 percent. The 90 percent upper confidence limit of 26

percent was used as the edible portion for white perch.

For brook trout and pickerel, two species for which no field data were available, a default value of

30 percent was used in accordance with EPA guidelines (EPA, 1989).

Each angler who had creeled fish was asked to indicate the number of individuals who would be

sharing the creeled catch. This value was assumed to be constant for all of the angler's fishing

trips, and it was used rather than household size because it was recognized that there might be

members of an angler's household who do not consume freshwater fish. Although adults and

children were tallied separately by the survey clerk, no distinction was made between adults and

children in calculating consumption rates.

To estimate the angler's weekly fishing frequency for the season, anglers were asked to report the

number of trips to the West Branch taken prior to the interview. The number of reported trips to

the river to date was used to estimate weekly frequency, assuming that fishing frequency remained

constant throughout the season. For example, if a fisherman reported that he had taken two trips to

the river since the beginning of the fishing season, and the fishing season had been underway for

eight weeks, his weekly frequency was estimated at 0.25 trips per week.

The fishing season on the West Branch lasts from April 1 to September 30, for a total of 183 days

(26.1 weeks). For the purpose of this study, it was assumed that the length of the fishing season

was 26 weeks.

Standard reporting of fish consumption rates is on an average daily basis. As there are no

commercial sources of local freshwater fish in Maine, only fish caught during the fishing season

were included in the estimates of consumption. Because anglers may freeze, smoke, or can a

portion of their catch for consumption during the winter months, the daily fish consumption rate

was annualized.

3.0 Results

To calculate a fish consumption rate, only those resident anglers who caught and retained their fish

were included. A total of 78 resident anglers who had creeled fish were interviewed during the

course of the survey. For estimating consumption, none of the interviews were repeat contacts.

Of these 78 anglers, 36 (46 percent) individuals fished Section A and 42 (54 percent) fished

Section B. Seventy-four (95 percent) of the anglers interviewed indicated that they intended to

consume or share the fish they had creeled. The estimated frequency of fishing trips ranged from

0.05 to 6 trips per week.

The number of individuals sharing a catch ranged from one to eight individuals when combining

Sections A and B. In Section A, the number of individuals sharing a catch ranged from one to

seven. In Section B, the number of individuals sharing a catch ranged from one to eight. Of the

total number of individuals reported to share the catch, 75 percent were adults and 25 percent were

children.

As described previously, average fish consumption rates were estimated for the persons

consuming each angler's catch. Fish consumption rates ranged from a low of 0.013 g/day to a

maximum of 98 g/day for one angler who creeled 0.59 kg (1.3 Ib) of whole fish and reported that

it would be consumed entirely by one adult. This angler reported a fishing frequency of six trips

per week. As equal success is assumed for each trip taken, this maximum estimate is extremely

conservative. It is unlikely that this single angler will fish six days/week for the entire fishing

season and catch 0.59 kg of fish on every trip.

For the consuming angling population interviewed in Sections A and B combined, a median fish

consumption rate was estimated to be 1.3 g/day with a 75th percentile of 3.7 g/day and a 95th

percentile of 11 g/day. For consuming anglers interviewed on Section A, the median fish

consumption rate was estimated to be 2.5 g/day with a 75th percentile of 4.8 g/day and a 95th

percentile of 11 g/day. For Section B, the median consumption rate for consuming anglers was

0.90 g/day with a 75th percentile of 2.2 g/day and a 95th percentile consumption rate of 10 g/day.

The mean consumption rates for consuming anglers in Sections A and B combined is 5.1 g/day

and corresponds to the 84th percentile of calculated consumption rates (Table 2). On Section A,

the mean consumption rate of 8.1 g/day corresponds to the 89th percentile of calculated

Table 2. Analysis of Fish Consumption Rates for Consuming Anglers on the West Branch

Combined Reaches Section A Section B

Number of Cases a

74 35 39

Minimum*3 0.013 0.35 0.013

Median (50th Percentile)b>c 1.3 2.5 0.90

75th Percentileb>c 3.7 4.8 2.2

Arithmetic Meanb 5.1 8.1 2.3

Percentile at the Meanc 84th 89th 82nd

c90th Percentileb- 8.4 9.0 3.9

95th PercentilebtC 11 11 10

Maximum13 98 98 23

a. Includes only those individuals who indicated that their creeled catch was intended for consumption. b. Grams/person-day. c. Calculated based on rank without assuming a statistical distribution.

8a

consumption rates. Similarly, the mean rate of 2.3 g/day calculated for Section B corresponds to

the 82nd percentile.

It is important to note that because the fish consumption rates are positively skewed rather than

symmetrically distributed, the arithmetic mean is not an appropriate descriptive measure of the

center of the distribution. The median, or 50th percentile, is a more physically relevant central

tendency measure for a skewed dataset because 50 percent of the consumption rate estimates lie

above the median and 50 percent fall below the median. Consequently, the median values provide

the most representative consumption rate estimates for each of the angler populations. Therefore,

we have defined the "typical individual" as that individual who is consuming freshwater fish at the

rate observed at the center of the distribution.

Notched box plots were created for fish consumption rates from Section A and Section B (Figure

4) to determine if the observed differences in consumption rates were statistically significant.

Notched box plots provide a simple graphical summary of the observed fish consumption rates

(McGill et al., 1978). Creating a notched box plot does not require assuming a statistical

distribution for the data. The plots show approximately the 25th percentile, the median, and the

75th percentile of the fish consumption rates, all of which are measures of location in a dataset that

are resistant to the impact of a few extreme values (Hoaglin et al., 1983). Additionally, the notches

centered on the median in each plot represent the approximate 95 percent confidence interval on the

median. Because the confidence intervals about the median consumption rates do not overlap for

the two sections, the median consumption estimates are statistically different at approximately the

95 percent confidence level (McGill et al., 1978). Additional information on the interpretation of

notched box plots is provided in Appendix A.

Figure 4. Notched Box Plots for Fish Consumption by Fishing Location

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0.01 Section A Section B

Fishing Location

9a

4.0 Discussion

An important factor in determining safe levels of chlorinated compounds in ambient waters is a

consideration of fish consumption. Since lipophilic compounds like 2,3,7,8-TCDD tend to

bioaccumulate in the fatty tissues of fish, it is necessary to consider the exposure of anglers who

catch and consume these fish.

Recently, a peer review panel of experts for the EPA has recommended that the median provides

the most accurate estimate of lifetime exposure through fish consumption (EPA, 1991). Results of

the West Branch creel survey indicate that the median fish consumption rate for the typical

consuming fisherman from that river is 1.3 g/day.

It is likely that fish consumption rates have been overestimated in this study as there are several

biases associated with choosing the West Branch as a study area. Portions of the West Branch are

tailwaters of hydroelectric facilities. The tailwater effect produces an enriched environment that

results in increased populations of resident invertebrates and fish. In addition, smelt from the

impoundments move downstream into riverine reaches where they provide food for salmon and

other species. The availability of this additional food increases the size and improves the condition

of the fish over those observed in other landlocked salmon fisheries. In addition, access for

fishermen is enhanced as a result of unique recreational agreements and leases between landowners

and the State. Thus, it is likely that more fish and larger fish are harvested from the West Branch

study area than would be harvested from other riverine landlocked salmon fisheries in Maine.

Therefore, the results of this creel survey likely overstate consumption that would be observed on

other free-flowing waters in Maine.

Notched box plots show that the median consumption rate for Section B (0.90 g/day) is

significantly lower than that for Section A (2.5 g/day) at an approximate 95 percent confidence

level. Several factors may contribute to the difference. As discussed, the landlocked salmon

fishery in Section A is world-renowned. High angler use and effort, in combination with the

desirability of landlocked salmon and brook trout as food fish, may account for increased

consumption within Section A. Conversely, although Section B contains a popular smallmouth

bass fishery, the lower popularity of the species as a food fish may account for the lower

consumption rates within Section B. It is also conceivable that the presence of industrial

discharges in Millinocket might result in lower consumption rates in Section B.

10

Several conservative assumptions were used throughout this analysis. It was assumed that success

rate is constant for the individual anglers. If an angler had creeled a fish at the time of the

interview, it was subsequently assumed that on each of his or her previous and future fishing trips,

the angler creeled an equivalent amount of fish. It was also assumed that the reported frequency

of fishing trips taken before the time of the interview would continue throughout the remainder of

the season.

These assumptions almost certainly result in overestimated rates of consumption for consuming

anglers and their families for two key reasons. First, fishing pressure is generally highest during

the spring and early summer due to greater availability of fish during that time (Spear, Personal

Communication, 1991). Thus, the frequency of fishing trips is likely to decrease as the season

progresses, rather than remain constant. Second, as demonstrated in the Saco River Creel Survey

(ChemRisk, 1991b), a high percentage of fishing trips are unsuccessful. To assume that an

individual who creeled fish on the day of the interview will creel fish on every trip taken during the

season is highly conservative. This potential overestimation is further exaggerated for those

individuals who reported a high frequency of fishing trips.

Appendix B provides an analysis of the uncertainty associated with these consumption rate

estimates. Using fisheries management data simultaneously collected from the West Branch

(Spear, 1991), the trends in participation and harvest rates over the season were identified. These

trends were then used to derive monthly adjustment factors for fishing frequency and harvest rates.

These monthly adjustment factors were incorporated into a Monte Carlo computer simulation to

derive a distribution of consumption rates for the West Branch that incorporates seasonal

fluctuations. Results of the analysis indicate that the median rate of consumption is likely to be 0.5

g/day, lower than the estimated median reported in Table 2 by a factor of 2.7.

Additional overestimation may have occurred due to survey bias. Chase and Harada (1984) have

reported that individuals tend to over-report their participation in recreational activities. Factors that

affect over-reporting include the length of the recall period, the frequency of fishing trips, the

interest in or importance of the activity to the individual, and the perceived social desirability of the

activity (USFWS, 1989). As a result, the reported frequencies of fishing trips taken previous to

the interview may be overstated, particularly for more avid anglers and for those interviewed later

in the season.

11

The Penobscot River supports significant landlocked salmon, smallmouth bass, and white perch

fisheries and is a target fishing area for many anglers. The presence of these fisheries, coupled

with the river's pristine nature and its high recreational usage, make the West Branch a

conservative choice for assessing riverine fishing habits in Maine. Despite the desirability of the

West Branch as a fishing location, the results of this study indicate that the consumption of

freshwater fish from the West Branch is low.

12

5.0 References

Chase, D.R., and M. Harada. 1984. Response error in Self-reported recreation participation. Journal of Leisure Research 15(4):322-329.

ChemRisk. 199 la. Consumption of Freshwater Fish by Maine Anglers. ChemRisk. Portland, ME. March 26.

ChemRisk. 1991b. Saco River Creel Survey. ChemRisk. Portland, ME. June 21.

Ebert, E.S. 1991. Edible portion of smallmouth bass and landlocked salmon in Maine Rivers. Memorandum from E. S. Ebert to W.E. Taylor. January 11.

EPA. 1991. Peer Review of Land Application of Sludge from Pulp and Paper Mills Using Chlorine and Chlorine-Derivative Bleaching Processes: Proposed Rule For Human Dietary and Ecotoxicologic Risks. Prepared for the U.S. Environmental Protection Agency, Office of Toxic Substances. October.

EPA. 1989. Assessing Human Health Risks from Chemically Contaminated Fish and Shellfish: A Guidance Manual. U.S. Environmental Protection Agency. Office of Marine and Estuarine Protection. Office of Water Regulations and Standards, Washington, DC. EPA-503/8-89-002. September.

Fiore, Beth Jones, H.A. Anderson, L.P. Hanrahan, L.J. Olson, and W.C. Sonzogni. 1989. Sport fish consumption and body burden levels of chlorinated hydrocarbons: A study of Wisconsin anglers. Arch. Env. Health 44(2):82-88.

Hoaglin, E.G., F. Mosteller, and J.W. Tukey. 1983. Understanding Robust and Exploratory Data Analysis. John Wiley and Sons, Inc. New York.

Honstead, J.F., T.M. Beetle, and J.K. Soldat. 1971. A Statistical Study of the Habits of Local Fishermen and Its Application to Evaluation of Environmental Dose, A Report to the Environmental Protection Agency by Battelle Pacific Northwest Laboratories, Richland, WA 99352. (cited in TetraTech, 1986).

Humphrey, Harold E.B. 1976. Evaluation of Changes of the Level of Polychlorinated Biphenyls (PCB) in Human Tissue. Michigan Department of Public Health. Final Report on FDA Contract 223-73-2209. June.

McGill, R., J.W. Tukey, and W.A. Larsen. 1978. Variations in box plots. Am. Stat. 32(l):l2-\6.

MelFW. 1990. Statewide Trends for fishing on Maine's Inland Waters as Indicated by Creel Surveys, Voluntary Angler Reports, and License Sales from 1969 to 1989. Maine Department of Inland Fisheries and Wildlife. Job F104.

Turcotte, M-D.S. 1983. Georgia Fishery Study: Implications for Dose-Calculations. E.I. DuPont de Nemours & Co., Arkeu, SC. Sponsored by Department of Energy, Washington, DC. DE86-008041. Augusts.

13

USFWS. 1989. Investigation of Possible Recall/Reference Period Bias in National Surveys of Fishing, Hunting and Wildlife-Associated Recreation. Final Report. Contract no. 14-16-009-87­008. Prepared by Westat, Inc. Rockville, MD. December.

Velleman, P.P., and D.C. Hoaglin. 1981. Applications, Basics, and Computing of Exploratory Data Analysis. Boston: Duxbury Press.

Wilkinson, L. 1989. SYGRAPH: The System for Graphics. SYSTAT, Inc. Evanston, Illinois.

14

APPENDIX A

INTERPRETATION OF NOTCHED Box PLOTS

APPENDIX A Interpretation of Notched Box Plots

Notched box plots are simple graphical summaries of five important features of data sets: ( 1 )

location; (2) spread; (3) skewness; (4) tail length; and (5) outlying data points. Notched box plots

are variations on the box plot which additionally display the approximate 95% confidence limits on

ihe median (McGill et al., 1978). These plots are a useful tool in exploratory data analysis and in

preparing visual summaries of data (McGill et al., 1978). The notched box plots presented in this

report were created using SYSTAT version 5.0 (Wilkinson, 1989) and a Macintosh SE/30

computer.

Figure A-l presents a diagram of a notched box plot and labels its features. A notched box plot is

characterized by a central box wi th two "whisker" lines extending from it (Wilkinson, 1989)

Asterisks or open circles may be plotted outside the two "whiskers." Location is summarized

w i t h i n a plot by the median, which is displayed as the crossbar in the interior of the central box.

The ends of the central box, called fourths or hinges, give an indication of the spread of the data.

By definition, the central fifty percent of the observed values fall within the limits of the central

box. Just as the median splits the ranked data in half, the fourths split the remaining halves in half

again. The lower fourth or hinge corresponds approximately to the 25th percentile (i e , first

quartile, or Qi) of the observed values, while the upper fourth or hinge corresponds approximately

to the 75th percentile (i.e., third quartile, or Cb) of the observed values. The length of the central

box shows the fourth-spread of the data, which is comparable to the interquartile range. The

relative position of the median, lower fourth, and upper fourth give an indication of the skewness

of the data. If the median is much closer to the lower fourth than to the upper fourth, the data is

positively skewed, i.e., the observations are not symmetrically distributed but rather are clumped

near the lower end of the scale. Because the fish consumption rates presented in this report were

>o positively skewed, use of a logarithmic scale was necessary to show detail on the box plots.

The plot's "whiskers" provide an indication of tail length, another measure of data spread

(Velleman and Hoaglin, 1981). The limits of the whiskers are called the inner fences. By

definition, the lower inner fence is located 1.5-times the fourth-spread below the lower fourth.

Similarly, the upper inner fence is located 1.5-times the fourth-spread above the upper fourth.

Another set offences, known as the outer fences, are located at 3-times the fourth-spread below

and above the fourths. Outer fences are not displayed on notched box plots. Asterisks appearing

on the plot represent individual observations outside the inner fences but within the outer fences.

A-l

Figure A-l. Notched Box Plot Diagram

Upper Inner Fence Q3 + 1.5(Q3-Q1)

Upper Fourth Q3 Upper Conf. Limit

(approx. 95%) Whiskers

Fourth-spread Median Q3-Q1

Lower Conf. Limit (approx. 95%)

Lower Fourth Ql

Lower Inner Fence Ql - 1.5(Q3-Q1)

Outside Values <Q1 ­ 1 .5(Q3-Ql)but > Q 1 - 3 ( Q 3 - Q 1 )

Far Outside Value <Q1-3(Q3-Q1)

A-la

Open circles represent observations outside the outer fences. Both asterisks and open circles

indicate outlying values.

Notched box plots also include confidence intervals on the median at approximately the 95% level

(McGill et al., 1978). The confidence intervals are shown as notches beginning at the median and

returning to full width at the lower and upper confidence limits. Notched box plots are useful for

comparing results among several groups. If the plotted confidence intervals do not overlap, then

one can be confident at about the 95% level that the population medians are different. Conversely,

if confidence intervals do overlap, then populations medians are not significantly different at

approximately the 95% confidence level.

A-2

APPENDIX B

UNCERTAINTY ANALYSIS

APPENDIX B Uncertainty Analysis

When survey data pertaining to consumption of fish were collected for the West Branch, anglers

were interviewed only one time and only if they held fish in their creels. During that single

interview, information was gathered on the size and number of fish creeled at the time of the

interview, and the number of individuals with whom the anglers reported that they intended to

share their creeled catch. In addition, anglers were asked how many trips to the river they had

taken up to and including the time of the interview. In order to calculate a daily rate of

consumption of West Branch fish over the entire year, it was necessary to estimate the number of

additional trips to the river the angler would likely take during the remainder of the season, and to

estimate the percentage of the time that the individual would be successful at creeling a fish for

consumption. Because the data collected were obtained during a single event, the year-long

extrapolation required making assumptions about the frequency of future trips and the success rate

for those trips.

The frequencies of fishing trips by the individual anglers were estimated by dividing the total

number of previous trips reported by the angler at the time of the interview by the number of weeks

of the fishing season that had elapsed. While this was a reasonably accurate method for estimating

the frequency of trips already taken by the angler, assumptions had to be made about how each

angler's frequency of trips was likely to change during the remainder of the season. Absent

evidence to the contrary, ChemRisk assumed that the angler's reported frequency for past trips

would remain constant for the remainder of the season and that on every previous and subsequent

fishing trip, the angler creeled the same weight of fish as that measured in his creel at the time of

the interview.

Both of these assumptions are likely to overpredict actual consumption rates. The frequency of

fishing trips is highly variable during fishing season due to differences in weather conditions and

changing availabilities of target species. A review of the consumption data indicates that 85 percent

of the anglers with creeled fish were interviewed in May and June with the greatest number of

anglers interviewed in June (Table B-l). After June, the number of interviews dropped

considerably, because in addition to there being fewer anglers on the river to interview, the

percentage of those anglers who had creeled fish was also lower.

B-l

Table B-l. Monthly Distribution of Interviews in Consumption Survey

... . Number of Month ,Interviews

Aprila NA

May a 16

June 46

July 8

August 3

September 2

a. Survey was begun on May 26, 1990 NA = Not available

B-la

This trend can also be seen in the unpublished data gathered from Georgia Pacific's simultaneous

fisheries management survey of the Penobscot River (Table B-2; Spear, 1991). In that survey, the

greatest number of anglers fishing the river was observed in the month of June with steady

decreases during the months of July, August, and September. At the same time, the number of

fish creeled followed the same pattern. Anglers in June creeled the greatest number of fish per

angler (average of 0.26 fish per angler). However, by September, the average was only 0.076

fish creeled per angler. Thus, even if an angler did fish with the same frequency as that reported

early in the season, he or she was much less likely to creel fish at the same rate during the latter

part of the season. To assume that an angler will fish with the same frequency and harvest rate

throughout the season is very likely to overpredict the angler's level of participation and harvest for

the season.

To quantify the degree of overestimation likely to be found in the consumption rate estimates

reported in Table 2, ChemRisk used a Monte Carlo computer simulation. Monte Carlo computer

simulations can be used to more explicitly define the distribution of the populations by repeatedly

solving an equation based on the probability distribution for each defined parameter that has been

defined (EPA, 1989). Once the relevant distributions have been entered, the simulation selects

randomly from each distribution to solve the equation (EPA, 1989). Through repeated iterations, a

distribution of the results is created. The Monte Carlo method eliminates reliance on a single point

estimate for each parameter, allowing the full range of possible values and integrating their

likelihoods of occurrence. The Monte Carlo analysis allows factors to be introduced that can adjust

for variations in the individual parameters over the season, resulting in a more realistic range of

fish consumption values.

Several steps were necessary to prepare the distributions for input into the Monte Carlo analysis.

These included:

• Identification of the distribution of the minimum consumption rates for the anglers.

• Identification of the distribution of weekly fishing frequencies calculated for each

angler up to and including the date of the interview.

B-2

Table B-2. Distribution of Angler Participation and Harvest by Month3

Percent of No. of Anglers Total Observed Number of Fish per

Month Observedb for Season0 Fish Harvestedd Angler6

April 899 9.6 109 0.12

May 1.161 12.4 112 0.097

June 2,778 29.8 711 0.26

July 1,902 20.4 229 0.12

August 1,632 17.5 161 0.097

September 964 10.3 73 0.076

Total 9,336 100 1,395

a. From simultaneous Georgia Pacific fisheries management survey for the West Branch (Spear, 1991). b. Includes all resident and nonresident anglers observed regardless of whether they had creeled fish. c. (Number of anglers observed during month)+(Total number of anglers for season). d. Total number of fish creeled by observed anglers. e. (Number of fish harvested during the month)-i-(Number of anglers observed during month)

B-2a

• Estimation of the monthly variations in the number of trips taken per month by

Penobscot River anglers, based on the larger dataset collected as pan of the

simultaneous fisheries management survey conducted by Georgia Pacific.

• Identification of the distribution of the number of fish creeled per angler by the

interviewed anglers.

• Estimation of the monthly variations in the number of fish creeled per angler based

on the larger dataset collected as part of the simultaneous fisheries management

survey.

Each of these factors is discussed below.

Minimum Consumption Rate

The theoretical minimum consumption rates for each angler are based only on the data collected

during the interview. The minimum rate assumes that the angler creeled no fish on trips taken prior

to the date of the interview, and would catch no additional fish for the remainder of the season,

(i.e., one trip per year). A minimum consumption rate estimate was derived for each angler

interviewed using the following equation:

Qn = Wj x P x T x I/Hi x 1/D

Where:

Cm = Minimum consumption rate (g/person-day)

Wj = Total weight of fish caught and creeled by angler i (g whole fish/trip)

P = Edible portion (g edible/g whole fish)

T = Trips per year (1 trip per year)

Hj = Number of persons who share angler i's catch (persons)

D = Total days per year (365 days/year)

For example, if the angler had creeled 1 fish with a total weight of 1 kg, it was assumed that 30

percent of that fish (300 g) was edible (EPA, 1989). Then, if the angler reported that he intended

B-3

to share that fish with 2 other household members, it was estimated that each of the 3 individuals

would consume 100 g of fish. To annualize that consumption rate, the 100 g was divided by 365

days so that it estimated the minimum rate of consumption for that angler, 0.27 g/day. Table B-3

reports the distribution of the calculated minimum consumption rates for the 74 anglers interviewed

for the consumption survey who indicated that they intended to consume their catch.

Distribution of Frequency of Fishing Trips

The frequency of fishing trips for each individual angler was estimated by dividing the number of

trips reported by the angler to have been taken up to and including the day of the interview by the

total number of weeks that had elapsed during the fishing season. Thus, if an angler was

interviewed on the 10th week of fishing season and reported that this was his first trip to the river,

the total of 1 trip divided by 10 weeks resulted in an estimated weekly frequency of 0.10

trips/week. This was then multiplied by 26 weeks/year (the total number of weeks of open water

fishing season) to derive a frequency of 2.6 trips per year.

Table B-4 reports the distribution of the frequency of fishing trips reported by the anglers

interviewed for the consumption portion of the survey. The estimated frequencies were quite low

for most of the anglers; 45 percent were estimated to take 2.6 or fewer trips per year. The

maximum number of trips per year was estimated to be 156 trips per year. This frequency was

estimated for two individuals who were interviewed early in June and who indicated that they had

fished nearly every day since the beginning of fishing season.

Adjustment Factor for Frequency of Fishing Trips

Because anglers were not likely to maintain a constant fishing frequency throughout the season, a

monthly adjustment factor for the frequency of fishing trips taken was derived using the data

collected as part of the Georgia Pacific fisheries management survey (Spear, 1991). Data from that

survey were sorted by month so that the number of anglers per month could be established. In

order to adjust frequency rates, all monthly frequencies (anglers/month) were normalized to June

which had the highest number of interviews and was assigned a factor of 1. The relative values

assigned to the other months are reported in Table B-5 and are based on the relative percentages of

the total interviews during the season that were represented by the number of interviews reported

for each individual month.

0

Table B-3. Distribution of Calculated Minimum Fish Consumption Rates

Number of Cases 74

Minimum 0.01b

Median (50% Percenule)c 0.29 b

75lh percentilec 0.49 b

Mean 0.38b

Percentile at the Mean c 65th

90lh pcrcenulec 0.69b

95th perccntilec 1 2

a. Based on [Weight of fish creeled at time of interview x 30% edible portion] + [number of persons sharing catch x 365 days]

b. g/person-day c. Calculated based on rank without assuming a statistical distribution.

B-4a

Table B-4. Distribution of Frequency of Fishing Trips Reported in Consumption Survey (trips/year)

Number of Trips per Individuals Year

s 10.4 13

2 15'6

3 18.2 2 20.8 , 26.0

78

2 156

B-4b

a Table B-5. Distribution of Angler Participation by Month

Month of Interview

No. of Anglers Observed

Percent of Total Observed

Adjustment Factor for

MontlJ3

April 899 9.6 0.322

May 1,161 12.4 0.416

June 2,778 29.8 1

July 1,902 20.4 0.684

August 1,632 17.5 0.587

September 964 10.3 0.346

Total 9,336 100

a. From Georgia Pacific Fisheries Management Survey database for Penobscot River. (Spear, 1991) b. Normalized to June.

B-4c

Distribution of Number of Fish Creeled per Trip

The distribution of the number of fish creeled per trip was determined from the data collected at the

time of the interview. At the time of the interview, 61 percent of the successful anglers

interviewed had 1 fish in their creel that they intended to consume, and 18 percent had 2 fish

(Table B-6). The remaining individuals interviewed had creeled between 3 and 15 fish that they

intended to consume.

Adjustment Factor for Number of Fish Creeled per Angler

The estimated adjustment factors for the number of fish creeled per angler during each month were

derived based on the data collected as part of Georgia Pacific's simultaneous fisheries management

survey (Spear, 1991). Data were sorted so that the number of fish creeled per angler could be

established for each month (Table B-7). In order to adjust harvest rates, all monthly frequencies

were normalized to June which was assigned a value of 1. The values assigned to the other

months are reported in Table B-7 and were based on the relative percentages of the numbers of fish

creeled per angler during each month.

Monte Carlo Analysis

The following equation was used for the Monte Carlo simulation:

Cadjj = Cm x A

Where:

Cadjj = Average adjusted consumption rate for persons consuming catch of angler i

(g/person-day)

Cm = Minimum consumption rate (g/person-day)

A = Adjustment factor (unitless)

B-5

Table B-6. Distribution of Fish Creeled and Intended for Consumption by Interviewed Anglers

Number of Individuals

45

13

5

1

2

4

1

2

1

Fish Creeled per Angler

1

2

3

4

5

6

7

8

15

B-5a

Table B-7. Distribution of Fish Creeled per Angler by Month and Adjustment Factors

Number of Fish Adjustment Month of Number of Fish Anglers per Factor for Interview Harvested3 Observed Angler0 Monthb

April 109 899 0.12 0.462

May 112 1,161 0.097 0.373

June 711 2,778 0.26 1.00

July 229 1,902 0.12 0.462

August 161 1,632 0.097 0.373

September 73 964 0.076 0.292

a. From Georgia Pacific fisheries management survey of West Branch (Spear, 1991) b. (Total fish creeled during month)/ (Total number of anglers observed during month) c. Normalized to June.

B-5b

The adjustment factor (A) is a multiplier that takes into account increases above the minimum

consumption rate that one would expect to see due to additional fish caught during the additional

trips taken during the season. It is defined as follows:

dj X At X W^ X Aw

Where:

A = Adjustment factor (unitless)

Tadj = Adjusted frequency of trips compared to minimum frequency

(trips taken / trips taken,™)

At = Seasonal adjustment factor for trips per year (unitless)

Wadj = Adjusted weight of fish creeled per trip compared to minimum (fish weight per

trip / fish weight per tripmin)

Aw = Seasonal adjustment factor for fish per trip (unitless)

The following distributions were entered into the Monte Carlo analysis:

• the full distribution of calculated minimum consumption rates based on the weight

of a single day's catch, a 30 percent edible portion, the number of individuals

reported to share the catch, and an assumption of one trip per year (Cm);

• the weighted distribution of trip/year frequencies as reported by the anglers (Tadj);

• the fishing frequency adjustment factors for each month of fishing season. These

factors were all weighted equally (At);

• the weighted distribution of the number of fish creeled per interviewed angler as

reported during the interview (Wadj); and,

• the fish per angler adjustment factors for each month of fishing season. These were

also weighted equally (Aw).

B-6

The adjustment factors for fishing frequency and fish creeled per trip were dependent variables.

This is because each factor was derived for an individual month. Thus, if an individual iteration of

the simulation randomly selected the fish per angler adjustment factor for August, it also selected

the fishing frequency adjustment factor for August

Results

Twenty thousand iterations that randomly picked from the five separate input distributions were

run for the Monte Carlo analysis. The median rate of consumption (50th percentile) estimated by

the uncertainty analysis was 0.49 g/day with a 75th percentile of 1.6 g/day and a 95th percentile of

10.7 g/day (Table B-8). The mean rate of consumption was estimated to be 3.0 g/day and appears

to fall between the 80th and 85th percentile of the simulated consumption rates.

Discussion

The results of the Monte Carlo simulation indicate that the consumption rates are lower when

adjustment factors relating to the seasonality of fishing activity and fish availability are considered

(Table B-8). Differences are greatest at the lower end of the consumption rate scale as the median

is lower by a factor of approximately 2.7 while the 95th percentile is approximately the same as

that reported in Table 3 of the original analysis.

These results are reasonable when one considers that the highest consumers are likely to be the

more avid anglers. Avid anglers are more likely to fish with a constant frequency than are anglers

for whom fishing is a lower priority. Thus, the assumption originally used in estimating

consumption rates, that frequency remains constant over the season, is more likely to be true for

the higher consumers who are also the more avid anglers. In addition, more avid anglers are likely

to be more skilled fishermen and have greater rates of harvest than occasional fishermen. Thus,

the original assumption, that fish creeled per trip remains constant over the season, may be a

reasonable assumption for the more skilled anglers as they are more likely to obtain fish when fish

availability is low than are those individuals who are not as skilled.

However, for the majority of anglers, the rates reported in Table 3 most likely overpredict actual

fish consumption by more than a factor of 2. As the fishing season on the West Branch

progresses, fish become more difficult to catch. Fishing trips taken later in the season are likely to

B-7

Table B-8. Comparison of Monte Carlo Simulation Results with Original Consumption Rate Estimates

N of Cases

Minimum

Median

75th percentile

Mean

90th percentile

95th percentile

a Combined reaches, Table 2 b. g/person-day

Original Estimates

74

0013b

1.3"

3.7b

5.1b

8.4 b

l l b

Monte Carlo Simulation

74

00013b

0.49 b

1.6b

30b

53b

107b

B-7a

result in decreased harvests. In addition, as harvest success decreases with progress of the season,

it is reasonable to infer that less avid anglers will not be as likely to maintain their fishing

enthusiasm and trip frequency.

The results of this uncertainty analysis indicate that the consumption rate estimates reported in

Table 2 may be overpredicted by as much as a factor of 2. This overprediction is the result of the

seasonal variations in fishing effort and fish availability that occur during the open water season.

Adjusting consumption rate estimates to incorporate these seasonal variabilities results in

substantially lower estimated rates of consumption than those reported in Table 2.

In addition, because the West Branch is located in a remote area with a low population density, it is

likely that many of the anglers who use the fishery must travel some distance to reach the river. As

a result, they are likely to make fewer trips that are longer in duration than would a local angler.

Consequently, while their fishing intensity might be high during the time that they are in proximity

to the river, it is likely that their fishing intensity is much lower when considered for the entire

season. Thus, the original assumption that frequency would remain constant throughout the

remainder of the season is unlikely for the great majority of these individuals and would, almost

certainly, result in a considerable overprediction for the composite rate of fish consumption from

the West Branch.

B-8