Biomonitoring of Environmental Status and Trends (BEST)

Program: Environmental Contaminants and their Effects on

Fish in the Yukon River Basin

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Scientific Investigations Report 2004—5285

U.S. Department of the Interior

U.S. Geological Survey
Front cover: The Alaska state map shows the Yukon River Basin (green) and staions sampled in this study (orange). Shown in gray

(inset map) are major river basins and stations in the conterminous U.S. sampled during other Biomonitoring of Environmental Status

and Trends (BEST) Program investigations.
Biomonitoring of Environmental Status and

Trends (BEST) Program: Environmental

Contaminants and their Effects on Fish in

the Yukon River Basin

By Jo Ellen Hinck, Timothy M. Bartish, Vicki S. Blazer, Nancy D. Denslow, Tim S.

Gross, Mark S. Myers, Patrick J. Anderson, Carl E. Orazio, and Donald E. Tillitt

Scientific Investigations Report 2004—5285

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Hinck, J.E., Bartish, T.M., Blazer, V.S., Denslow, N.D., Gross, T.S., Myers, M.S., Anderson, P.J., Orazio, C.E., and Tillitt, 

D.E., 2004, Biomonitoring of Environmental Status and Trends (BEST) Program: Environmental Contaminants and their 

Effects on Fish in the Yukon River Basin: U.S. Geological Survey, Columbia Environmental Research Center, Columbia, 

Missouri, Scientific Investigations Report 2004—5285, 87 p.
Preface iii

Preface

The study described in this report was conducted as part of the U.S. Geological Survey (USGS) 

Biomonitoring of Environmental Status and Trends (BEST) Program. BEST evolved from 

previous Federal monitoring programs including the National Pesticide Monitoring Program 

(NPMP) of the 1960s, renamed the National Contaminant Biomonitoring Program (NCBP) in 

the early 1970s, which also screened for elemental contaminants. The U.S. Fish and Wildlife 

Service (USFWS) participated in the NPMP and maintained the NCBP by monitoring concentrations of persistent contaminants in freshwater fish and avian wildlife through 1986. The 

BEST Program was initiated in the 1990s to build on information produced by these earlier 

programs and to provide more biologically relevant information regarding potential contaminant effects on lands and species under USFWS management. The program was transferred 

to the National Biological Survey in 1993 and ultimately to USGS in 1996. The Large River 

Monitoring Network of BEST has principal emphasis to identify, monitor, and assess the 

effects of chemical contaminants on the fish health in the nation’s large rivers. The 2002 

Yukon River Basin (YRB) study represented a continuation of studies conducted in the Mississippi River Basin in 1995 and the Columbia River and Rio Grande Basins in 1997. 

Acknowledgements

This study was conducted jointly by the USGS through its research centers in Columbia, 

Missouri (Columbia Environmental Research Center, CERC), Gainesville, Florida (Florida 

Integrated Science Center), and Kearneysville, West Virginia (Leetown Science Center, LSC); 

the Northwest Fisheries Science Center (NWFSC) of the National Oceanic and Atmospheric 

Administration (NOAA) in Seattle, Washington; and the U.S. Fish and Wildlife Service 

(USFWS) of Fairbanks, Alaska. The study was facilitated through a Research Work Order 

with the USGS-Florida Cooperative Fish and Wildlife Research Unit at the University of 

Florida (UF), Gainesville, Florida. Many individuals representing USGS, USFWS, UF, and 

other organizations contributed substantially during the conduct of the study. K. Mueller and 

A. Matz (USFWS) organized and supervised field portions of the study. C. Hemming, C.M. 

Hemming, T. Wertz, F. Anderson, C. Anderson, D. Nigro, J. Akaran, M. Annis, D. Nicks, and 

P. Anderson participated in field collections. R. Carroll, D. Bowers, and B. Bowers provided 

lodging during collections. E. Greer (CERC) provided fish samples for practice dissections. 

S. Yess (La Crosse USFWS) provided northern pike for a vitellogenin induction study, and A. 

Delonay (CERC) and R. Gordon and D. Elowiese of the Genoa National Fish Hatchery aided 

in the transportation of those northern pike. Chemical analyses were conducted by T. May, K. 

Echols, K. Feltz, J. Meadows, M. Tanner, G. Tegerdine, J. Arms, W. Brumbaugh, and M. Walther of the CERC Environmental Chemistry and Inorganic Chemistry laboratories. Laboratory 

analyses for biomarkers were performed by D. Nicks (CERC), D. Bowling (LSC), and K. Kroll 

(UF). D. Bowling (LSC), T. Lee (NWFSC), K. Spring (LSC), and M. Willis (NWFCS) assisted 

in the histology slide preparation, and E. Frankenberry (LSC) assisted with the macrophage 

aggregate evaluation. R. Brown (USFWS), and J. Candrl and A. Donahue (CERC) aged the 

fish. A. Donahue also produced report graphics. R. Lipkin (CERC) managed the bibliographic 

database and prepared the report for publication. D. Boyt, J. Fox, and M. Keuss provided quality assurance for tables and figures. Special thanks to C. Schmitt (CERC) who provided technical advice on the writing of the report. K. Mueller (USFWS), L. Verbrugge (state of Alaska), 

and A. Matz (USFWS) reviewed the report and provided additional information.
iv Environmental Contaminants and their Effects on Fish
Contents v

Contents

Preface .......................................................................................................................................................... iii

Acknowledgements..................................................................................................................................... iii

Abstract.......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Yukon River Basin Overview.............................................................................................................. 2

Hydrology and Environmental Setting..................................................................................... 2

Description of Population................................................................................................. 3

Land Ownership and Economy........................................................................................ 4

Water Quality Impairments and Fish Consumption Advisories.................................. 4

Extant Sources of Information on Contaminants in the Yukon River Basin ............................... 5

Major Sources of Contaminants to the Yukon River Basin........................................................... 6

Military Facilities......................................................................................................................... 6

Mining and Extractive Industries ............................................................................................ 6

The Trans-Alaska Pipeline System (TAPS).................................................................... 6

Air Pollution Patterns ................................................................................................................. 7

Industrial and Municipal Sources................................................................................... 7

Comprehensive Environmental Response, Compensation, and Liability Act ................... 8

Materials and Methods ............................................................................................................................... 8

Collection Sites .................................................................................................................................... 8

Target Species and Sampling Strategy............................................................................................ 8

Monitoring Methods Overview.......................................................................................................... 9

Field Procedures................................................................................................................................ 13

Fish Collection ........................................................................................................................... 13

Sample Processing................................................................................................................... 13

Laboratory Analysis........................................................................................................................... 14

Composite Sample Preparation.............................................................................................. 14

Elemental Contaminants and Moisture Content.................................................................. 14

Organochlorine Contaminants and Lipid Content ............................................................... 15

H4IIE Rat Hepatoma Cell Bioassay ........................................................................................ 16

EROD Activity............................................................................................................................. 16

Fish Health Indicators ....................................................................................................................... 17

General Histopathological Analyses ..................................................................................... 17

Quantitative Organism-Level Indicators ............................................................................... 17

Macrophage Aggregates ........................................................................................................ 17

Reproductive Indicators ................................................................................................................... 17

Gonadal Histopathology .......................................................................................................... 17

Vitellogenin ................................................................................................................................ 20

Steroid Hormones..................................................................................................................... 20

Data Set Composition and Statistical Analyses ........................................................................... 21

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

Geographic Distribution and Demographic Characteristics of the Fish Collected................. 22

Accumulative contaminants, H4IIE Bioassay, and EROD Activity............................................. 24

Elemental Contaminants................................................................................................................... 24

Arsenic ....................................................................................................................................... 24

Selenium..................................................................................................................................... 25
vi Environmental Contaminants and their Effects on Fish

Mercury...................................................................................................................................... 26

Lead............................................................................................................................................. 29

Cadmium..................................................................................................................................... 30

Zinc.............................................................................................................................................. 30

Copper......................................................................................................................................... 31

Chromium and Nickel............................................................................................................... 32

Organochlorine Chemicals............................................................................................................... 32

DDT and Its Primary Metabolites........................................................................................... 32

Cyclodiene Pesticides.............................................................................................................. 34

Chlordane and Heptachlor............................................................................................. 34

Dieldrin .............................................................................................................................. 34

Endrin................................................................................................................................. 36

Other Organochlorine Compounds ........................................................................................ 36

Mirex.................................................................................................................................. 36

Toxaphene......................................................................................................................... 36

Hexachlorocyclohexanes (HCH) ................................................................................... 37

Hexachlorobenzene (HCB)............................................................................................. 38

Total PCBs, H4IIE-Derived Dioxin Equivalents, and EROD Activity............................................ 38

Total PCBs .................................................................................................................................. 38

H4IIE Bioassay .......................................................................................................................... 38

Ethoxyresorufin O-Deethylase (EROD) Activity ................................................................... 39

EROD in Northern Pike.................................................................................................... 39

EROD in Longnose Sucker.............................................................................................. 39

EROD in Burbot ............................................................................................................... 39

Accumulative Contaminants, H4IIE, and EROD: Summary ......................................................... 43

Fish Health Indicators ....................................................................................................................... 43

Organism-Level Indicators...................................................................................................... 43

External Gross Lesions ................................................................................................... 43

Health Assessment Index............................................................................................... 44

Condition and Organosomatic Indices.................................................................................. 44

Condition and Organosomatic Indices in Northern Pike........................................... 44

Condition and Organosomatic Indices in Longnose Sucker .................................... 45

Cellular and Histopathological Indicators ............................................................................ 48

Macrophage Aggregates ............................................................................................... 48

MA-#..... .................................................................................................................... 48

MA-Size.................................................................................................................... 49

MA-%........................................................................................................................ 50

Fish Health Indicators: Summary .................................................................................................... 51

Reproductive Biomarkers................................................................................................................. 54

Gonadal Histopatholgy, Vitellogenin, and Steroid Hormones ........................................... 54

Female Northern Pike ..................................................................................................... 55

Male Northern Pike ......................................................................................................... 56

Female Longnose Sucker............................................................................................... 58

Male Longnose Sucker................................................................................................... 60

Reproductive Biomarker: Summary................................................................................................ 61

Spatial patterns in contaminant concentrations and biomarker responses ........................... 63

Geographic Summaries ........................................................................................................... 63

Correlations Between Contaminant Concentrations and Biological Endpoints ............ 67
Contents vii

Summary and Conclusions........................................................................................................................ 67

References................................................................................................................................................... 68

Appendix 1 ................................................................................................................................................... 83

Appendix 2 ................................................................................................................................................... 85

Figures

1. Map of the Yukon River Basin................................................................................................................ 3

2. Gonadal stages and atresia in female fish ovaries.......................................................................... 18

3. Gonadal stages in male fish testes..................................................................................................... 19

4. Concentrations of arsenic and selenium by station and species in whole body fish composite 

samples collected in the Yukon River Basin in 2002............................................................ 25

5. Concentrations of mercury by station and species in whole body fish composite samples collected in the Yukon River Basin in 2002 ................................................................................. 29

6. Concentrations of cadmium by station and species in whole body fish composite samples 

collected in the Yukon River Basin in 2002............................................................................ 30

7. Concentrations of zinc, copper, chromium, and nickel by station and species in whole body 

fish composite samples collected in the Yukon River Basin in 2002................................. 31

8. Weighted geometric mean concentrations of p,p’-DDT, DDE, and DDD by station in whole 

body fish composite samples collected in the Yukon River Basin in 2002....................... 34

9. Concentrations of p,p’-DDE, toxaphene, total chlordanes, and dieldrin by station and species 

in whole body fish composite samples collected in the Yukon River Basin in 2002....... 36

10. Weighted geometric mean concentrations of chlordane-related compounds by station in 

whole body fish composite samples collected in the Yukon River Basin in 2002........... 37

11. Concentrations of total PCBs by station and species in whole body fish composite samples 

collected in the Yukon River Basin in 2002............................................................................ 38

12. Hepatic microsomal EROD activity by station in female and male northern pike and longnose 

sucker collected in the Yukon River Basin in 2002............................................................... 44

13. Fish health indicators by station in female and male northern pike collected in the Yukon 

River Basin in 2002..................................................................................................................... 49

14. Fish health indicators by station in female and male longnose sucker collected in the Yukon 

River Basin in 2002..................................................................................................................... 51

15. Splenic macrophage aggregate parameters by station in northern pike collected in the 

Yukon River Basin in 2002......................................................................................................... 53

16. Splenic macrophage aggregate parameters by station in longnose sucker collected in the 

Yukon River Basin in 2002......................................................................................................... 53

17. Gonadal stage of female and male northern pike collected in the Yukon River 

Basin in 2002............................................................................................................................... 56

18. Reproductive health indicators by station in female northern pike collected in the Yukon 

River Basin in 2002..................................................................................................................... 58

19. Reproductive health indicators by station in male northern pike collected in the Yukon River 

Basin in 2002............................................................................................................................... 60

20. Gonadal stage of female and male longnose sucker collected in the Yukon River Basin in 

2002 .............................................................................................................................................. 61

21. Reproductive health indicators by station in female longnose sucker collected in the Yukon 

River Basin in 2002..................................................................................................................... 62

22. Reproductive health indicators by station in male longnose sucker collected in the Yukon 

River Basin in 2002..................................................................................................................... 62

23. Maximum concentrations of mercury and selenium in composite samples of whole fish..... 65
viii Environmental Contaminants and their Effects on Fish

24. Plasma vitellogenin in male northern pike and longnose sucker................................................ 66

25. Ratio of estradiol to 11-ketotestosterone in northern pike and longnose sucker..................... 67

Tables

1. Stations sampled in 2002 and collection date..................................................................................... 9

2. Methods incorporated into the YRB project in 2002 ........................................................................ 10

3. Organochlorine chemical and elemental contaminants measured in whole body fish composite samples.................................................................................................................................. 11

4. Monitoring and assessment strategy for polycyclic aromatic and polyhalogenated 

hydrocarbons ............................................................................................................................. 13

5. Number of fish collected, organized by species, station, and gender in the Yukon 

River Basin in 2002..................................................................................................................... 22

6. Lengths, weights, and ages of northern pike collected in the Yukon River Basin in 2002......... 23

7. Lengths, weights, and ages of longnose sucker and burbot collected in the Yukon River Basin 

in 2002 .......................................................................................................................................... 24

8. Percent of samples and stations that exceeded limit of detection concentrations for elemental contaminants in composite samples of whole fish from the Yukon River Basin in 

2002 .............................................................................................................................................. 26

9. Unweighted geometric mean, minimum, and maximum concentrations of elemental contaminants in fish collected in the Yukon River Basin in 2002 ..................................................... 27

10. Spatial trends of chemical contaminants in fish collected in the Yukon River Basin 

in 2002 .......................................................................................................................................... 28

11. Percent of samples and stations with concentrations exceeding the limit of detection for 

organochlorine chemical residues in composite samples of whole fish in the Yukon 

River Basin in 2002..................................................................................................................... 33

12. Unweighted geometric mean, minimum, and maximum concentrations of organochlorine 

chemical contaminants in fish from stations in the Yukon River Basin in 2002 .............. 35

13. Results of preliminary analysis of variance investigating the effects of various factors on 

biomarker responses in northern pike and longnose sucker in the Yukon River 

Basin in 2002............................................................................................................................... 40

14. Geometric mean and range of microsomal EROD activities (pmol/min/mg protein) in fish collected in the Yukon River Basin in 2002 ................................................................................. 45

15. Number and location of external lesions identified on fish collected in the Yukon River Basin 

in 2002 .......................................................................................................................................... 46

16. Distribution of Health Assessment Index (HAI) scores among northern pike, longnose 

sucker, and burbot collected in the Yukon River Basin in 2002.......................................... 47

17. Arithmetic mean of condition factor and hepatosomatic index by species and station in 

northern pike, longnose sucker, and burbot collected in the Yukon River Basin 

in 2002 .......................................................................................................................................... 48

18. Arithmetic mean of splenosomatic index by species, gender, and station in northern pike, 

longnose sucker, and burbot collected in the Yukon River Basin in 2002 ........................ 50

19. Arithmetic mean of macrophage aggregate density, macrophage aggregate area, and percent tissue occupied by macrophage aggregate by species, gender and 

station in northern pike, longnose sucker, and burbot collected in the Yukon River 

Basin in 2002............................................................................................................................... 52

20. Arithmetic mean of gonadosomatic index, vitellogenin, and atresia by gender, species, and 

station in northern pike, longnose sucker, and burbot collected in the Yukon River 

Basin in 2002............................................................................................................................... 57
Contents ix

21. Arithmetic mean of estradiol, eleven-ketotestosterone, and ratio of E/KT by gender, species, 

and station in northern pike, longnose sucker, and burbot collected in the Yukon River 

Basin in 2002............................................................................................................................... 59

22. Summary of chemical and biological indicator results by Yukon River Basin station............. 64

23. Significant Spearman rank correlations between biomarkers and contaminants................... 68

Appendix 1. Nominal Method Detection Limits and results of quality assurance for 

organochlorine chemicals analyzed in whole body fish composites 

collected in the Yukon River Basin in 2002............................................................................ 84

Appendix 2. Histological observations in northern pike, longnose sucker, and burbot 

collected in the Yukon River Basin in 2002............................................................................ 86

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in)

millimeter (mm) 0.03937 inch (in)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 0.3861 square mile (mi)

cubic kilometer (km3) 0.2399 cubic mile (mi3)

Volume

milliliter (mL) 0.03381 fluid ounce (fl. oz)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

cubic meter (cm3) 0.0002642 million gallons (Mgal)

Mass

kilogram (kg) 2.205 pound, avoirdupois (lb)

Concentration

microgram per gram (μg/g) = part per million (ppm; 106)

nanogram per gram (ng/g) = part per billion (ppb; 109

)

picogram per gram (pg/g) = part per trillion (pptr; 1012)

milligram per millimeter (mg/mL) = part per thousand (ppt; 103

)

milligram per liter (mg/L) = part per million (ppm; 106

)

microgram per liter (μg/L) = part per billion (ppb; 109

)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8
x Environmental Contaminants and their Effects on Fish
Biomonitoring of Environmental Status and Trends (BEST)

Program: Environmental Contaminants and their Effects

on Fish in the Yukon River Basin

Jo Ellen Hinck1, Timothy M. Bartish2, Vicki S. Blazer

3

, Nancy D. Denslow4, Tim S. Gross5, Mark S. Myers6,

Patrick J. Anderson7, Carl E. Orazio1, and Donald E. Tillitt

1

Abstract

This project collected, examined, and analyzed 217 fish 

representing three species at 10 stations in the U.S. portion 

of the Yukon River Basin (YRB) from May to October 2002. 

Four sampling sites were located on the Yukon River; two 

were located on the Porcupine River, and one site was on each 

of the Ray, Tanana, Tolavana, and Innoko Rivers. Northern 

pike (Esox lucius), longnose sucker (Catostomus catostomus), 

and burbot (Lota lota) were weighed, measured, and examined in the field for external and internal lesions, and liver, 

spleen, and gonads were weighed to compute somatic indices. 

Selected tissues and fluids were collected and preserved for 

analysis of fish health and biomarker analyses. Composite 

samples of whole fish from each station were grouped by species and gender and analyzed for organochlorines and elemental contaminants and for dioxin-like activity using the H4IIE 

rat hepatoma cell bioassay.

Mercury and selenium were the only contaminants 

measured that exceeded wildlife guidelines or thresholds, 

and both had been identified as contaminants of concern in 

previous studies in the YRB. Concentrations of mercury 

1

U.S. Geological Survey, Columbia Environmental Research Center 

(CERC), 4200 New Haven Rd., Columbia, MO 65201.

2

U.S. Geological Survey, BEST Program, 2150 Centre Ave., Building C, 

Fort Collins, CO 80526.

3

U.S. Geological Survey, Leetown Science Center (LSC), 1700 Leetown 

Rd., Kearneysville, WV 24530.

4

Center for Environmental and Human Toxicology, PO Box 110885, University of Florida, Gainesville, FL 32611.

5

U.S. Geological Survey, Florida Integrated Science Center (FISC), 7920 

NW 71st St., Gainesville, FL 32653.

6

National Oceanic and Atmospheric Administration, Northwest Fisheries 

Science Center, 2725 Montlake Blvd., E, Seattle, WA 98112.

7

Johnson Controls, c/o USGS, 2150 Centre Ave., Building C, Fort Collins, 

CO 80526.

exceeded 0.1 μg/g ww in at least one species from every YRB 

station. One or more northern pike and burbot samples from 

stations on the Tanana River downstream of Fairbanks and on 

the Yukon River near Galena and The Bridge had concentrations of Hg >0.3 μg/g ww. Concentrations of selenium (>0.6 

μg/g ww) also exceeded wildlife criteria in fish samples collected near Fairbanks, The Bridge, near the Charley-Kandik 

confluence, and Fish Hook Bend. The natural weathering of 

rocks is believed to be the primary source of selenium to the 

YRB. Other studies have indicated that atmospheric deposition is currently the major contributor of mercury in the YRB 

although mining inputs have been reported historically. Fish 

accumulation of mercury remains a concern for indigenous 

people and commercial fisheries in the YRB.

Fish health and reproductive biomarkers did not indicate 

widespread responses to contaminants, but individual fish 

from sites throughout the basin expressed isolated responses. 

Concentrations of vitellogenin >0.01 mg/mL in male fish 

may indicate exposure to estrogenic compounds. Multiple 

male fish collected from near the Charley-Kandik confluence, Fairbanks, Galena, and Innoko had concentrations of 

vitellogenin >0.01 mg/mL. Steroid hormone concentrations 

(estradiol in female fish and 11-ketotestosterone in male fish) 

were low in northern pike and longnose sucker or both from 

most YRB stations. Other reproductive biomarkers and fish 

health indicators were normal in YRB fish. The health of fish 

was generally good and the concentrations of most chemical 

contaminants was low in the YRB. 

Introduction

The Yukon River and its major tributaries are considered 

the transportation corridor of the sparsely populated, roadless 

interior of Alaska. The river provides fish for subsistence living and drinking water for many rural villages. Other activi-
2 Environmental Contaminants and their Effects on Fish

ties in the basin include commercial fishing, mining, logging, 

tourism, and military uses (Brabets and others, 2000). Water 

quality data are limited for the Yukon River Basin (YRB) 

although reports indicate that variation in basin water chemistry is due to natural rather than anthropogenic activities 

(Brabets and others, 2000).

The Yukon River and several of its largest tributaries were studied during the summer of 2002 as part of the 

Biomonitoring of Environmental Status and Trends (BEST) 

Program’s Large River Monitoring Network (LRMN). The 

BEST Program is unique among national monitoring programs 

with its emphasis on characterizing the effects of environmental contaminants on the health of the biota and their supporting 

habitat. BEST accomplishes this by measuring chemical concentrations and by evaluating the physiological, morphological, and histopathological responses of contaminant exposure 

by the organism. The primary objective of this study was to 

document the occurrence and distribution of contaminants and 

their effects on fish in the YRB and to evaluate the potential 

risk represented by these contaminants to other biota. Secondary objectives were to compare biomonitoring results from 

the YRB to other major river systems in North America and 

to further define benchmarks for the quantification of longterm trends and interpretation of biomarker results. These 

latter objectives were achieved by building on the results 

of similar investigations conducted in the Mississippi River 

Basin (MRB) in 1995 (Schmitt, 2002a), the Rio Grande Basin 

(RGB) in 1997 (Schmitt and others, 2004), and the Columbia 

River Basin (CRB) in 1997 (Hinck and others, 2004). The 

2002 YRB project was also designed to evaluate the compatibility of the BEST LRMN with the USGS National Stream 

Quantity Accounting Network (NASQAN) program, which 

monitors concentrations of dissolved pesticides and other constituents in the waters of the largest U.S. rivers (USGS, 2001).

Findings of the 2002 YRB study are reported in this document. Data from this study have been incorporated into an 

interactive national database at: www.cerc.usgs.gov/data/best/

search/index.htm. Results from this study, together with those 

from similar investigations conducted in other river basins, 

will help resource managers and scientists assess contaminant 

impacts on fish and on wildlife and human consumers of those 

fish and to identify areas that warrant further investigation of 

contaminant threats.

Yukon River Basin Overview

Hydrology and Environmental Setting

The YRB is the fourth largest basin in North America; 

it drains 854,696 square kilometers (km2) and is fifth largest 

in terms of average discharge (Schumm and Winkley, 1994). 

As a result, the Yukon River is a major contributor of water 

and solutes to the Arctic Ocean and Bering Sea ecosystems 

(Aagaard and Carmack, 1989). The Yukon River originates 

from the Llewellyn Glacier near Atlin Lake in northwestern 

British Columbia (Brabets and others, 2000), flows more than 

3,219 km through the Yukon Territory of Canada and central 

Alaska, and empties into the Bering Sea. The basin receives 

most of its inflow from runoff from rainfall, snowmelt, and 

glacial melt with a mean annual discharge near its mouth of 

200,000 cubic feet per second (cfs) (Brabets and others, 2000). 

Most runoff occurs from May to September although timing varies throughout the basin depending on geological and 

geographical characteristics.

Major tributaries of the Yukon River include the Pelly, 

Stewart, White, Porcupine, Tolovana, Tanana, Tozitna, 

Nowitna, Koyukuk, and Innoko Rivers (Fig. 1; Brabets and 

others, 2000). The Porcupine River, the largest tributary, 

drains 116,449 km2 in the northeastern part of the YRB and 

has a mean annual discharge of 22,000 cfs. The Tanana 

River, the second largest tributary, drains the north side of the 

Alaska Range (114,736 km2) and has the greatest mean annual 

discharge (44,600 cfs) of all tributaries in the YRB. The 

Koyukuk River drains part of the Brooks Range (90,650 km2) 

and has the greatest mean annual discharge (27,200 cfs) in the 

western YRB. The Pelly, Stewart, and White Rivers drain the 

eastern portion of the basin in Canada.

Five general physiographic regions have been recognized in the YRB (Bostock, 1970; Wahrhaftig, 1965). Rolling 

topography and gentle slopes (37%) and low mountains (24%) 

are the largest regions followed by plains and lowlands (20%), 

moderately high rugged mountains (17%), and extremely high 

rugged mountains (2%). The ecology of the YRB is diverse 

with mountains, rolling plateaus, bottomlands, wetlands, and 

coastal plains and the basin has been divided into 20 ecological provinces (Gallant and others, 1995). The dominant ecoregions in the basin are Interior Forested Lowlands and Uplands 

(21.2%) and Interior Highlands (16.9%). Interior Forested 

Lowlands and Uplands have short warm summers and long 

cold winters and include lowlands and plateaus along the 

Yukon River that are underlain with permafrost. The Interior 

Highlands are found in much of the Tanana River Basin and 

have rounded low mountains and receive more precipitation 

than the surrounding lower altitude areas. Talbot and Markon 

(1986) classified 90% of the land cover in the YRB as needleleaf forest, tall and low shrublands, broadleaf forest, lichens, 

barren, and wet herbaceous with the majority (53.5%) identified as needleleaf forest dominated by white spruce in welldrained areas and black spruce in lowland areas. Permafrost is 

present in much of the YRB and acts as a barrier to infiltration 

that increases the likelihood of flash flooding in streams draining permafrost areas (Brabets and other, 2000). However, the 

melting and diminishing of permafrost has become a concern 

to many residents in the YRB.

The YRB has variable climate due to its large size and 

range of altitude of land surface (Brabets and others, 2000). 

All of the YRB except for the Yukon Delta is located in the 

continental zone that has great temperature extremes, and air 

temperature averages -5.6 ̊C. The Yukon Delta is in the transi-
YUKON

TERRITORY

INNOKO R 

YUKON R 

KOYUKUK R 

PORPUCINE R 

NENANA

R 

S$

#

S#

Introduction 3

$ Major Cities or Towns 

S# Best YRB Sampling Sites (2002) 

YRB Hydrology 

Landowership: 

Federal Lands 

Native Lands 

State Lands 

Military 

ALASKA

302 

303 Fort Yukon 

304 

S#$ 301 

The Bridge S#

307 

S#$ 306 

Eagle $

308 S Tanana # 305 $

$ S# S# TANANA R $ Fairbanks 

Galena Nenana 

309 

310 S#

$S#

Kotlik 

$

Holy Cross 

Figure 1. Map of the Yukon River Basin including international boundary, towns and villages, major tributaries, land ownership, and 

sites sampled in 2002. See Table 1 for station descriptions.

tion zone, which has an average air temperature of -2.8 ̊C. 

Precipitation ranges from 25 to 330 centimeters (cm) annually 

and approximately half of the precipitation falls as snow from 

November to March. High mountains may have snowfall 

year-round, where much of it is stored for long periods in 

glaciers and icefields. Historical climate records indicate a 

warming trend in interior Alaska near Fairbanks (Brabets and 

others, 2000).

Description of Population

The human population of the YRB is approximately 

126,000. Ten percent of these people maintain a subsistence 

lifestyle, and depend on the basin’s fish and game resources 

(Brabets and others, 2000). Whitehorse is the population center (23,000 residents in 1998) in the Canadian portion of the 

YRB (Environment Canada, 1999). Dawson (2,000 residents) 

and Faro (1,000 residents) are the next largest Canadian towns, 

and the remaining villages have populations ranging from 100 

to 500 residents. The greater Fairbanks area (Fairbanks and 

North Star Borough) is the center of the Alaskan population 

with 84,000 residents in 1996 (Alaska Department of Labor, 

1999). Approximately 12,000 other residents are located in 

43 YRB villages from the Canadian border to the mouth of the 

Yukon River. Village populations range from approximately 

30 to 800 people with typical villages having fewer than 300 

residents, and villages in the Yukon-Koyukuk Delta are larger 

than interior villages (K. Mueller, personal communication). 

Accessibility to many villages is restricted to water and air 

transportation, which isolates the villages from surrounding areas (Alaska Department of Community and Economic 

Development (ADCED), 2004a). 

Many villages in the Yukon-Koyukuk area have high 

proportions of Athabascan or Yup’ik natives in the population 
4 Environmental Contaminants and their Effects on Fish

who maintain a traditional lifestyle and diet (ADCED, 2004a). 

Subsistence living represents not only a food source but also 

a cultural tradition for many native populations, and villages 

are more dependent on subsistence living when roads are not 

available to transport fresh fruits and vegetables (ADCED, 

2004b; Egeland and others, 1998). The annual harvest of wild 

foods including fish, mammals, birds, shellfish, and plants has 

been estimated to range from 170 to 206 kg/person in rural 

areas of Alaska (ADCED, 2004b; Wolfe, 2000). The ADCED 

reported 65% of the subsistence diet is composed of fish, 

mostly salmon (Onchorhynchus spp.), in the Yukon-Koyukuk 

area (ADCED, 2004b). Therefore, the potential risk from contaminants in traditional diets is a concern in the region (Ballew 

and others, 2004; Egeland and others, 1998). 

Land Ownership and Economy

The YRB in Canada includes parts of two Canadian 

National Parks and several Habitat Protection Areas (Brabets 

and others, 2000) and 9% of the land area of the Canadian 

Yukon. The U.S. government owns 68% of the YRB in 

Alaska (Fig. 1). Four national parks cover 10% of the area, 

eight National Wildlife Refuges (NWRs) cover 32%, and lands 

managed by the U.S. Bureau of Land Management (USBLM) 

cover 22%. The U.S. military and native corporations each 

own 1% of the land.

Many villages in the YRB rely on Federal and state 

governments for employment opportunities (ADCED, 2004a; 

2004b). The ADCED (2004b) reported 24.2% of the population in the Yukon-Koyukuk area was below the poverty level 

in 2000, and unemployment rates were higher than statewide 

averages. These percentages are likely a reflection of the 

time and effort directed toward subsistence living and limited 

opportunities to earn money (ADCED, 2004b). It has been 

estimated that the replacement cost of wild harvest foods 

would be $3-5 per pound ($131-219 million annually), indicating the importance of subsistence living in the rural economy 

(Wolfe, 2000). 

Commercial fishing, fish processing, timber processing, 

oil and gas exploration, fur trapping, and mining are important 

economic activities in the YRB (ADCED, 2004b; Brabets and 

others, 2000). Commercial export fishery development has 

enabled subsistence-based villages to obtain a cash-oriented 

economy. Salmon including chinook (Onchorhynchus tshawytscha), chum (Onchorhynchus keta), and coho (Onchorhynchus kisutch) are the primary targets of commercial fishing 

in the YRB, and stocks have remained healthy because their 

spawning, rearing, and migration habitat remain largely undisturbed. However, declines in salmon populations are being 

reported (ADCED, 2004b; Brabets and others, 2000). Gross 

earnings from commercial fishing have dropped 78% (from 

approximately $1,250,000 to <$100,000) from 1995 to 2000 in 

the Yukon-Koyukuk area due to poor salmon runs (ADCED, 

2004b). 

Mining in the YRB has historically occurred in localized, 

discrete, headwater streams. Three gold mines are in operation in the YRB and include Illinois Creek mine near Galena, 

Fort Knox and associate mines near Fairbanks, and Pogo mine 

near Delta. Logging could add to the YRB economy as large 

tracts of Federal land are transferred into native corporations 

and state ownership and as local and export timber demands 

increase (Brabets and others, 2000). Currently, the Tanana 

River Basin is the primary logging area in the U.S. portion of 

the YRB.

Water Quality Impairments and Fish Consumption

Advisories

Waters (rivers, streams, lakes) that do not meet defined 

water quality standards are listed as impaired. Section 303(d) 

of the Clean Water Act requires each state to assess all surface 

waters and list those that are impaired. There are relatively 

few water bodies throughout the YRB on Alaska’s 2002/2003 

303(d) list (Alaska Department of Environmental Conservation (ADEC), 2003a). Most impaired rivers and streams are 

located in small drainages and are listed for turbidity, toxic 

metals, and petroleum products. Most impaired waters in the 

YRB are within or near the town of Fairbanks. These waters 

include the Chena River, Chena Slough, Garrison Slough, 

Goldstream Creek, and Noyes Slough. Two impairments are 

located within Denali National Park, and one impairment is 

located in Wrangell-St. Elias National Preserve within the 

upper Tanana River drainage.

Fifteen miles of the Chena River have been designated as 

100% impaired from petroleum hydrocarbons, oil, and grease 

in the sediment attributed to urban runoff from Fairbanks 

(ADEC, 2003a). These pollutants are also associated with 

the Chena Slough (for 13 miles) and the Noyes Slough (for 7 

miles) impairments. Mining activities are responsible for turbidity impairments within Denali National Park, Goldstream 

Creek, Birch Creek, and Crooked Creek drainages and metal 

impairments [manganese (Mn), arsenic (As), iron (Fe), copper 

(Cu), and cadmium (Cd)] on Cabin Creek within WrangellSt. Elias National Preserve (ADEC, 2003a). The impairment 

of Garrison Slough has been attributed to polychlorinated 

biphenyls (PCB) waste (contaminated sediments and waste 

disposal) from Eielson Air Force Base and although remediation activities have occurred, this waterway remains on the list 

until remedial actions result in attaining water quality standards (ADEC, 2003a).

The U.S. Environmental Protection Agency’s (USEPA) 

National Listing of Fish and Wildlife Advisories (NLFWA) 

database was queried for any advisories for any pollutants 

within Alaska (USEPA, 2003a). Restrictions have not been 

placed for consuming fish from any waterbody within the state 

by the USEPA or the state of Alaska. The state of Alaska 

evaluated fish contaminant data from Alaska and the human 

health implications of fish consumption and recommended the 

unrestricted consumption of fish from Alaskan waters (Alaska 
Introduction 5

Department of Health and Social Services (ADHSS), 2001; 

Egeland and others, 1998).

Extant Sources of Information on Contaminants

in the Yukon River Basin

Water quality in the YRB has not been as extensively 

studied as other large U.S. river basins. The Yukon River 

drains an extensive landscape, and most water quality studies 

have focused on particular areas or regions within the basin. 

In addition, the YRB has considerably fewer anthropogenic 

impacts and has generally been considered pristine compared 

to other large U.S. river basins. However, rising concerns over 

atmospheric mercury (Hg) deposition and metal contamination 

from mining have led to contaminant studies within the YRB. 

Information for local contaminant sources such as permitted discharges, fish consumption advisories, and hazardous 

waste sites has been made available through USEPA databases 

including the Toxic Release Inventory (TRI), Permit Compliance System (PCS), and the Comprehensive Environmental 

Response, Compensation, and Liability Information System 

(CERCLIS). These databases provided information for U.S. 

facilities and sites only.

Comparatively few national or regional investigations 

have focused on the YRB. The National Contaminant Biomonitoring Program (NCBP) collected fish from one YRB site 

(Station 305) from 1969 to 1986 and analyzed organochlorine 

and elemental contaminants (Schmitt and others, 1999b). The 

NASQAN program recently completed an environmental 

and hydrologic overview of the YRB that includes information on water quality issues, specifically carbon cycling and 

Hg (Brabets and others, 2000). The Canadian government 

performed a national contaminant study from 1997 to 2003 as 

part of its Northern Contaminants Program (NCP). Summaries of contaminant impacts pertaining to the physical environment, human health issues, and biological impacts have 

recently been published (NCP, 2003). Data were available for 

the headwaters of the Yukon River within the Yukon Territory. 

The NCP reported that predatory freshwater fish, specifically 

burbot (Lota lota), contained high concentrations of Hg, and 

concentrations were increasing in some lakes, especially Lake 

Laberge. Concentrations of organic contaminants were much 

lower than Hg. However, concentrations of toxaphene in 

burbot livers exceeded consumption guidelines in fish collected from Lake Laberge, although concentrations have been 

decreasing since the mid-1990s.

There are eight NWRs managed by U.S. Fish and Wildlife Service (USFWS) located within the YRB. These include 

the Arctic, Yukon Flats, Kanuti, Nowitna, and Tetlin NWRs in 

eastern Alaska and Koyukuk, Innoko, and Yukon Delta NWRs 

in western Alaska. The USFWS has studied contaminant 

issues in multiple YRB NWRs since the late 1980s, and data 

are available for water, sediment, fish, and mammals. Mueller 

and others (1995) reported northern pike (Esox lucius) consistently had the greatest concentrations of Hg, and longnose 

sucker (Catostomus catostomus) consistently had the greatest 

concentrations of Cd and Cu in Kanuti NWR. Concentrations of metals were not anticipated to be problematic in fish 

including northern pike and longnose sucker in the Koyukuk 

and Northern Unit of the Innoko NWRs (Snyder-Conn and 

others, 1992), although in a subsequent study from these 

NWRs, concentrations of Hg and selenium (Se) in fish muscle 

were greater than background concentrations from other areas 

(Mueller and others, 1996). The USFWS (Mueller and Matz, 

2000) reported Fort Wainwright Army Base and Eielson Air 

Force Base near Fairbanks were a probable local source of 

PCB and dichlorodiphenyltrichloroethane (DDT) contamination to the Tanana River and the city of Fairbanks. Another 

study determined that pesticides and dioxins were not at concentrations of concern in northern pike or burbot from a YRB 

lake (Snyder-Conn, 1992). 

The ADEC was established to conserve and monitor 

natural resources and the environment within the state (ADEC, 

2003b). The ADEC has a fish monitoring project that analyzes methylmercury (MeHg), lead (Pb), and Cd in multiple 

marine fish species and northern pike from various lakes 

within the YRB (ADEC, 2003b). The project was initiated to 

determine if concentrations of heavy metals in Alaskan fish 

were below concentrations justifying consumption advisories. 

The ADEC concluded that concentrations of methylmercury were low and not a public health concern in frequently 

consumed fish, especially salmon. The ADEC also monitors 

illegal releases of contaminants including oil and diesel spills 

into the environment. Many YRB stations sampled in 2002 

including near the Charley-Kandik confluence, Fort Yukon, 

Kotlik, Tanana, and Fairbanks were in the vicinity of airstrips. 

All of these locations had small spills reported from leaking 

petroleum tanks, some of which contaminated surrounding 

soils (ADEC, 2003c). The ADEC has an ongoing investigation of two underground 1 million-gallon tanks (one diesel and 

one jet fuel) that have leaked into the soil and potentially into 

the groundwater near Galena. Fairbanks also had multiple 

reported incidents including pipeline spills and high concentrations of PCBs at some facilities, as well as trichloroethene 

contamination in groundwater (ADEC, 2004a).

Most YRB contaminant studies have been limited to 

reporting chemical concentrations. Biomarker studies in the 

YRB are extremely limited and available only for specific species and locations. Therefore, the primary basis of comparison 

for biomarkers and contemporary concentrations of contaminants in whole fish is previous BEST LRMN Program data 

from the MRB (Schmitt, 2002a), RGB (Schmitt and others, 

2004) and CRB (Hinck and others, 2004), which included fish 

species collected in the YRB.
6 Environmental Contaminants and their Effects on Fish

Major Sources of Contaminants to the Yukon

River Basin

Activities such as mining and logging brought nonindigenous people to the YRB in the 1800s. As a result, military services were brought to the basin to provide law and order to the 

land, and several large bases and test ranges were established 

that have contributed to surface water, groundwater, and sediment contamination within the YRB. Many mining districts 

for gold and other precious metals were established prior to 

concerns about potential impacts on the environment and have 

resulted in contaminant problems. In addition, contamination 

from the transport and exploration of crude oil continues to be 

a concern throughout Alaska. Air patterns provide a pathway 

for contaminants sources to enter the region and result in the 

primary mechanism of pollutant load to the YRB.

Military Facilities

Active military bases and test ranges are major contributors of non-point source pollution in the YRB (Yukon River 

Inter-Tribal Watershed Council (YRITWC), 2002). Contaminants at these locations include petroleum products, solvents, 

pesticides, batteries, and asbestos, although water quality data 

associated with these non-point source pollutants is lacking.

The U.S. Department of Defense is responsible for environmental restoration of properties known as formerly used 

defense sites (FUDS) that were previously owned or utilized 

by the Federal government and under the jurisdiction of the 

Secretary of Defense. The locations of FUDS were acquired 

from the U.S. Army Corps of Engineers (USACE) geographic 

information system (GIS) data layer (USACE, 1999), and 

information on contaminants associated with FUDS was 

obtained from the Formerly Used Defense Site Geographic 

Information System (USACE, 2003). Approximately 113 of 

600 FUDS in Alaska are located in the YRB. Most FUDS are 

positioned along the major river corridors with many in the 

Tanana River Basin, centrally located near Fairbanks. Other 

clusters of FUDS are at Delta Junction, Tok, Tanacross, and 

Galena. At least 12 sites within the basin are known to have 

hazardous chemical compounds. Sites often contain ordnance, 

above- and below-ground storage tanks, drums, transformers, 

landfills, and spill areas. Hazardous materials known to occur 

at FUDS include trichloroethane (TCE), PCBs, pesticides, 

radioactive waste, and various petroleum and fuel-related 

compounds. Seven sites are known or suspected to be disposal 

sites for chemical weapons. These sites are located at Fort 

Greely, Fort Wainwright, and the Gerstle River test sites near 

Healy Lake.

Mining and Extractive Industries

Mining occurred in the YRB since the mid-1880s discovery of gold in the upper Yukon Basin along the Fortymile 

River. Early discoveries formed the Fortymile, Eagle, and 

Circle mining districts prior to the famous Klondike Gold 

Rush in Canada’s Yukon Territory in 1896. Mining activities 

have since taken place throughout the basin. The most frequently mined commodities are gold and other precious metals, Pb, zinc (Zn), coal, and more recently diamonds (mostly in 

the Yukon Territory, Canada). The area between Tanana and 

Eagle along the U.S.-Canada border continues to be one of the 

most productive gold producing areas within the basin. Most 

of the 800 past producing mines located in the U.S. portion of 

the basin are clustered around Circle, Livengood, Fairbanks, 

Wiseman, Eagle, and Tanana (Causey, 1998). Almost 90% 

of these mines were placer operations with 10% being lode 

operations (hard rock mining).

Impacts from unregulated mining and abandoned mines 

have been documented for more than 100 years in the YRB. 

Panning and using small sluice boxes were the most common 

forms of placer mining until the 1920s when mining practices 

included more destructive methods such as large-scale hydraulic and dredging operations. Today some of these mines are 

designated USEPA Superfund sites and on the Alaska Department of Energy (DOE) list of contaminated sites. Past mining 

operations have also contributed to the designation of impaired 

streams and rivers. Mines that do not fall into a specific category for cleanup or remediation and for which a technically 

responsible party to maintain or reclaim a site is not named 

pose additional challenges (YRITWC, 2002). Mining impacts 

such as habitat disturbance and contamination by trace metals 

have been cited as adversely affecting anadromous fisheries 

within the YRB (Buhl and Hamilton, 1990; Salomone and 

Bergstrom, 2004; USFWS, 1986; 1991).

The Trans-Alaska Pipeline System (TAPS)

The TAPS was built in 1974-1977 and transports crude 

oil from the North Slope of Alaska 800 miles south to Port 

Valdez in Prince William Sound. Over 13 billion barrels of 

crude oil have moved through TAPS, contributing approximately 11% of U.S. domestic oil production (USBLM, 

2002). The peak daily flow of 2.03 million barrels per day 

was reached in 1988 with the current rate approximately at 

1 million barrels per day (USBLM, 2002). The infrastructure of the pipeline valves and pump stations is strategically 

placed to facilitate movement of crude oil, isolate sections 

of the pipeline for maintenance, and minimize the volume of 

potential spills. There are six pump stations along the TAPS 

within the YRB; however, some of these stations are being 

phased out (TAPS Owners, 2001). TAPS crosses numerous creeks and large rivers in the YRB including the Yukon, 

Koyukuk, Tanana, Tolovana, Chena, Salcha, and Delta, many 

of which are classified as sensitive and critically sensitive 
7

habitats to resident and anadromous fisheries (TAPS Owners, 2001). TAPS owners and regulatory agencies identified 

numerous environmental impacts attributed to the operation of the pipeline (TAPS Owners, 2001; USBLM, 2002). 

Impacts associated with contaminant inputs relate primarily 

to oil spills, water discharges, and emission of volatile organic 

compounds (VOCs) from valves and pump stations. Activities 

associated with the pipeline that have affected water quality 

are construction, excavation, and maintenance of the pipeline, 

material sites and quarries, dewatering, permitted discharges, 

handling hazardous materials, and spills. However, impacts 

from these activities have not been associated with irreversible 

or irretrievable effects on water quality (TAPS Owners, 2001; 

USBLM, 2002).

Spills were identified as the greatest concern for continued operation of the pipeline (TAPS Owners, 2001; USBLM, 

2002). In addition to crude oil, the pipeline also contains 

hazardous materials and other hydrocarbon-based compounds 

that are injected into the pipeline to increase flow efficiency 

and reduce shipping and handling costs (TAPS Owners, 2001). 

A large oil spill on land would be expected to have localized effects on vegetative communities, birds and mammal 

populations, and on fish populations in adjacent water bodies 

(TAPS Owners, 2001; USBLM, 2002). Past operation of the 

pipeline resulted in numerous spills within the YRB although 

most were small and localized (TAPS Owners, 2001). Five 

large spill events occurred within the YRB between 1978 and 

2001, resulting in over 24,000 barrels of spilled crude (ADEC, 

2003c; TAPS Owners, 2001). The most recent spill associated with TAPS within the YRB (October 4, 2001) resulted 

in 285,600 gallons of crude being spilled within 1 mile of the 

Tolovana River (ADEC, 2003c).

Another pipeline that has been associated with contaminants in the YRB is the Haines-Fairbanks Pipeline, originally 

used by the U.S. Army (1954–1973) to transport petroleum 

products from Haines to military bases near Fairbanks and into 

Canada. The U.S. Army reportedly used a mixture of 2,4-

dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) to maintain the 326 miles of pipeline 

corridor (ADEC, 2003d). ADEC recently reported that dioxin 

contamination associated with this mixture of compounds did 

not pose a health threat (ADEC, 2004b).

Air Pollution Patterns

Ocean and atmospheric currents are key pathways for 

long-range transport of heavy metals, organic pollutants, and 

radionuclides from industrial and agricultural sources to arctic 

regions (NCP, 2003). Global air transport of pollutants is the 

primary mechanism by which the YRB receives the majority of its pollutant load. In general, concentrations of many 

heavy metals and organic pollutants are declining in northern 

Canada and Alaska; however, Hg remains a concern. Mercury 

is deposited from the atmosphere onto the snow surface during 

Hg depletion events and is linked to polar sunrise (MacdonIntroduction

ald and others, 2003; NCP, 2003). Climate change may also 

modify atmospheric and ocean currents in the future causing 

more contaminants to reach the Arctic Ocean (Macdonald and 

others, 2003; NCP, 2003). In addition, increased temperatures 

may also lead to an increase in the distribution of wetlands 

with the melting of permafrost causing sinks for Hg deposition 

(Macdonald and others, 2003).

The U.S. National Park Service (USNPS) operates two 

air deposition monitoring sites within the YRB located near 

the northeast corner of Denali National Park and Preserve 

and at Poker Flat northeast of Fairbanks. Both sites are part 

of the Clean Air Status and Trends Network (CASTNet) that 

measures dry deposition of atmospheric chemical compounds. 

Deposition of atmospheric sulfur-containing and nitrogenous 

compounds was measured following CASTNet Protocols at 

these sites from July 1998 to June 2001 and a third site located 

south of the YRB to compare ambient air quality at Denali 

National Park and Preserve against regional conditions (Air 

Resource Specialist Inc. and Cahill, 2003). Concentrations 

of sulfur-containing and nitrogenous compounds from these 

sites were low compared to other CASTNet sites across the 

U.S. Seasonal trends and timing of peak concentrations among 

all three sites for sulfates, sulfur dioxide, particulate nitrate 

and ammonium, and gaseous nitric acid indicated most of the 

measured compounds are from regional sources and not local 

sources. These results support other studies that document 

global transportation of anthropogenic emissions to the Arctic 

(AMAP, 1998; Macdonald and others, 2003).

Industrial and Municipal Sources

Records describing the location of regulated industrial 

and municipal facilities and the types and amounts of chemicals released were reviewed. Location and discharge data for 

permitted facilities operating in the U.S. portion of the YRB 

were derived from the USEPA’s TRI and Permit Compliance 

System (PCS). The TRI database contains basic facility information and chemical data on facilities that release toxic chemicals and compounds to the air, surface water, land, underground injections, and transfers to off-site locations. Only 

those facilities reporting releases to surface water, air (fugitive 

and stack), and on-site lands for the years 1997 through 2001 

were included in the review for this report (USEPA, 2003b). 

The PCS database contains information on facilities permitted 

through the National Pollutant Discharge Elimination System 

(NPDES) to discharge effluent into navigable waters. Records 

for all major and minor permitted dischargers located in the 

YRB were reviewed from the PCS database (USEPA, 2003c).

Fourteen industrial facilities reported releases of toxic 

chemicals within the YRB during 2001 according to the TRI 

database (USEPA, 2003b). Eleven TRI facilities are located 

at or near Fairbanks, Alaska, and other facilities are located at 

Healy, Delta Junction, and Clear, Alaska. Industry classifications for these facilities include National Security (military 

bases and training areas), power generation, gold ore mining, 
8 Environmental Contaminants and their Effects on Fish

petroleum refineries and storage, and chemical manufacturing. 

TRI facilities did not report permitted releases to any streams 

or rivers although two industrial facilities did report releases to 

on-site gravel pits and ponds. Facilities associated with Eielson Air Force Base near Fairbanks reported discharging small 

amounts of Hg (0.05 kg), Pb (4.5 kg) and dioxin or dioxin-like 

compounds (8 g) into a pond, and a petroleum refinery located 

in North Pole, Alaska discharged >340 kg (in 2000) and 11.3 

kg (in 2001) of benzene, toluene, and xylene compounds to a 

gravel pit. Large quantities of toxic chemicals and compounds 

were released in 2001 to on-site lands by six TRI facilities, 

which were among the top 10 Alaskan facilities for the largest 

on-site land releases. The Fort Knox mine near Fairbanks 

reported on-site land releases >6.8 million kg including Pb 

(709,609 kg), Cu (331,575 kg), Mn (4,466,977 kg), chromium 

(Cr) (865,454 kg), cyanide (205,930 kg), Hg (205 kg), nickel 

(Ni), nitrates, and ammonia compounds. Other compounds 

released by the remaining facilities include toluene, xylene, 

benzene, cumene, and similar aromatic compounds. Ten TRI 

facilities including three military bases, two power generators, two mining companies, two petroleum refineries, and a 

chemical manufacturing company also reported large amounts 

of toxic chemicals (362,874 kg in 2001) released to the air 

through stack and fugitive emissions and some were among 

the top 10 air-emitting Alaskan facilities. Barium (Ba) and Ba 

compounds were the most abundant toxic chemicals emitted (175,495 kg) followed by hydrochloric acid (35,267 kg), 

hydrogen fluoride (33,112 kg), chlorine (31,942 kg), phosphorus (24,276 kg), and ammonia (19,595 kg). Only 4.5 kg (4%) 

of the Hg emitted was considered fugitive emissions.

There are approximately 563 facilities within the YRB 

that are permitted to discharge to navigable waters, 548 of 

which are involved with gold ore production (USEPA, 2003c). 

The PCS database did not contain parameter discharge information for these operations, and most are involved with placer 

mining and discharge into small tributaries of the Fortymile, 

Tolovana, Chatanika, Chena, Tanana, and Koyokuk Rivers, 

Birch Creek, and the Yukon-Charley River confluence. Only 

three facilities are listed as a major dischargers (>3,700,00 L 

effluent/day), including a coal mine and a power generator in 

Healy and the wastewater treatment plant operated by the city 

of Fairbanks. Three additional power plants, two at Fairbanks 

and one at Eielson Air Force Base, ultimately discharge into 

the Chena River. The classification of the remaining NPDES 

facilities includes three facilities associated with petroleum 

production and transportation, an apartment complex, and a 

bus tour line. 

Comprehensive Environmental Response,

Compensation, and Liability Act (CERCLA -

Superfund) Site Summary

Documentation and Record of Decisions related to 

USEPA Superfund sites in the YRB were obtained through 

USEPA’s CERCLIS database (USEPA, 2003d). There are 19 

CERCLIS sites located within the YRB, and eight sites are 

located at Fairbanks or nearby military bases. The remaining 

sites are located at Delta Junction, Tanacross, Tanana, Galena, 

Eagle, Denali National Park and Preserve, Tok, and Northway. Thirteen of the sites are associated with past military 

activities. Other sites are a result of past mining, storage, and 

landfill activities. Two of the military sites, located on Fort 

Wainwright and Eielson Air Force Base, are currently on the 

USEPA Superfund National Priority List (NPL) for cleanup 

of hazardous substances. Contaminated media at the military 

sites include soil, groundwater, sediments, and surface water 

from numerous landfills, chemical dumps, drum burial sites, 

ordnance and detonations areas, broken pipelines, and spills. 

Contaminants include heavy metals (As, Hg, Cd), solvents, 

pesticides, paints, ordnance compounds and volatile organic 

compounds (benzene, xylene, trichloroethylene, and toluene). The Chena River, a tributary of the Tanana River, flows 

through some of the contaminated areas within Fort Wainwright. PCB-contaminated fish have been found in a slough 

that runs through the Eielson Air Force Base NPL site but not 

in the Tanana River (USEPA, 1998; 1999). A Fairbanks salvage yard situated on the floodplain of the Tanana and Chena 

Rivers is also on the NPL list for groundwater contamination 

with TCE and soil contamination with industrial solvents, 

PCBs, and Pb although contaminants have not been reported 

in the rivers (USEPA, 1995; 2003e).

Materials and Methods

Collection Sites

Fish were collected at 10 sites in the YRB in Alaska (Fig. 

1; Table 1). Four of the ten sites were located on the mainstem Yukon River; two sites were on the Porcupine River; and 

one site each was on the Ray, Tanana, Tolovana, and Innoko 

Rivers. Most fish were collected in early May to mid-July 

in 2002. Station 302 was sampled in mid-August 2002 and 

Station 305 was sampled multiple times with the last collection occurring in mid-October. Sampling at most sites was 

completed during one visit spanning 2-4 days.

Target Species and Sampling Strategy

This study was designed to establish baseline contaminant data for the Yukon River and major tributaries and to 

compare with other investigations based on composite samples 

of whole fish while accommodating the biological measurements incorporated into the overall investigation (Schmitt and 

Dethloff, 2000). Many of these biological measurements are 
Materials and Methods 9

Table 1. Stations sampled in 2002 and collection date (first-last) in the Yukon River Basin (YRB). Stations are 

listed upstream to downstream. 

Yukon 

Porcupine 

301 

302 

Nearby Landmark 

Near Charley-Kandik 

Confluence, AK 

Fish Hook Bend, AK 

Collection Dates 

6/5/02-6/6/02 

8/14/02-8/16/02 

Latitude, Longitude 

65°22’28.56”N, 142°30’20.88”W 

67°12’50.94”N, 142°09’58.56”W 

Porcupine 303 Fort Yukon, AK 6/12/02-6/14/02 66°35’21.06”N, 145°19’59.40”W 

Ray 

Tanana 

Tolovana 

304 

305 

306 

Near the Bridge, AK 

Fairbanks, AK 

Tolovana, AK 

6/4/02-6/7/02 

5/30/02-5/31/02, 

6/28/02, 10/10/02 

6/4/02-6/6/02 

65°53’01.26”N, 149°48’00.72”W 

64°45’02.52”N, 148°03’15.84”W 

64°56’56.40”N, 149°44’13.44”W 

Yukon 307 Tanana, AK 6/5/02-6/7/02 65°08’09.72”N, 152°24’54.72”W 

Yukon 

Innoko 

Yukon 

308 

309 

310 

Galena, AK 

Innoko NWR Field 

Station, AK 

Kotlik, AK 

6/10/02-6/14/02 

7/15/02-7/17/02 

5/9/02-5/12/02 

64°41’56.22”N, 156°58’36.30”W 

63°38’33.66”N, 158°00’43.56”W 

63°02’12.18”N, 163°34’22.56”W 

River 

Station 

Number 

gender-specific and require live or freshly killed individual 

fish. To standardize fish health and biomarker results, it was 

desirable to collect the same species at each site in the basin. 

Review of the literature determined that one of the most 

prevalent bottom-dwelling species was longnose sucker and 

the most prevalent predator species was northern pike. Thus, 

for this project, longnose suckers and northern pike were 

the targeted species at all sites. Burbot, a preferred alternate 

predator species, was collected when northern pike could not 

be obtained. The collection goal at each site was 10 individual 

fish of each gender of each species (one predator and one bottom-dwelling species). More than two species were collected 

at sites with incomplete quotas for the target predator species. Collectors were instructed to obtain adult fish of a size 

representative of those believed to be present based on extant 

information and to avoid extremely large or small fish.

Monitoring Methods Overview

A suite of chemical and biological methods was 

employed to characterize the exposure of fish to contaminants 

and the effects of exposure (Schmitt and Dethloff, 2000). The 

suite included reproductive biomarkers, measures of cytochrome P450 enzyme induction (to assess response to planar 

halogenated hydrocarbons (PHHs) and polyhalogenated 

aromatic hydrocarbons (PAHs), fish health assessments, and 

chemical analyses of fish carcasses (Table 2). Additional 

information on these methods is available elsewhere (see 

Schmitt, 2002a; Schmitt and Dethloff, 2000; Whyte and 

others, 2000; Whyte and others, 2004 and references cited 

therein). Concurrent determination of tissue residue concentrations along with the suite of fish health indicators and reproductive biomarkers supports the interpretation of relationships 

between exposure and biological responses.

The organochlorine and elemental contaminants analyzed 

in composite samples (Table 3) were selected to provide the 

maximum amount of information on accumulative contaminants of potential concern at minimal cost and to maintain 

continuity with the historical NCBP database (Schmitt, 

2002a). Extracts of the composite samples were screened 

with the H4IIE rat hepatoma cell bioassay (Whyte and others, 

2004), which responds to planar PHHs (Table 4). In addition, the livers of the individual fish were assayed for ethoxyresorufin O-deethylase (EROD) activity, which indicates 

recent exposure to exogenous AhR ligands including PHHs 

and PAHs (Kennedy and Jones, 1994; Pohl and Fouts, 1980; 

Whyte and others, 2000). Together, these assays and analyses 

allow estimation of the relative concentrations of potential 

biological effects of PHH and PAH, without the expense of 

instrumental analyses for these compounds (Table 4; Schmitt 

and others, 2002a).

Measures of fish health at various levels of biological 

organization, immune system responses, and reproductive status were included in the suite of indicators to address potential 

impacts from nonaccumulative contaminants and contaminant 
10 Environmental Contaminants and their Effects on Fish

Table 2. Methods incorporated into the YRB project in 2002. 

Method Description 

Tissue(s) 

Examined 

Primary 

Reference(s) Sensitivity 

Histopathology Microscopic examination for Liver, gill, Overall organism Hinton and others (1992); 

the presence of lesions; can gonads, spleen, health and Hinton (1993); Goodbred 

provide early indication of and kidney contaminants and others (1997) 

chemical exposure 

Ethoxyresorufin O- Enzyme induction by planar Liver PCBs; Pohl and Fouts (1980); 

deethylase (EROD) hydrocarbons chlorinated, Kennedy and Jones (1994); 

activity dioxins, and Whyte and others (2000) 

furans; PAHs 

Macrophage Macrophages are important in Spleen Multiple Blazer and others (1994); 

aggregate analysis the immune system, serving as contaminants Blazer and others (1997) 

a first line of defense for the including PAHs 

organism and as an antigen and metals 

processing cell 

H4IIE bioassay A screening tool to determine Whole fish PCBs; Tillitt and others (1991); 

the presence of certain classes (composite chlorinated Whyte and others (2004) 

of planar halogenated samples) dioxins and 

compounds furans 

Vitellogenin A precursor of egg yolk, Blood plasma Endocrine- Denslow and others (1999) 

normally synthesized in the modulating 

liver of female fish substances 

Steroid hormones Determine reproductive health Blood plasma Endorcrine- Guillette and others (1994); 

(estradiol and and status modulating Goodbred and others 

testosterone) substances (1997) 

Chemical analyses Organochlorine chemical Whole fish Specific analytes Schmitt and others 

residues and elemental (composite (1999a) 

contaminants samples) 

Somatic indices The relative mass of some Gonads, spleen, Overall organism Grady and others (1992) 

organs is often indicative of liver health 

chemical exposure 

Necropsy-based fish Visual assessment of All Overall organism Goede (1988, 1996); 

health external/internal anomalies (for health Adams and others (1993); 

assessment example, lesions, parasites, Adams (1990) 

tumors), which may indicate 

contaminant-related stress 

mixtures (Table 2). Measures of fish health included 1) gross 

observation of abnormalities; 2) condition and organosomatic 

indices; and 3) histopathological examination (Hinton and others, 1992; Hinton, 1993; Goodbred and others, 1997; Myers 

and Fournie, 2002). Gross observations and determination of 

indices based on relative fish and organ sizes such as condition 

factor (CF), hepatosomatic index (HSI), and splenosomatic 

index (SSI) are relatively simple and indicative of cumulative, 

organism-level changes (Grady and others, 1992). However, 

they are nonspecific in terms of causal mechanisms and may 

reflect early, subtle alterations and may foreshadow subsequent effects at the individual or population level.

Immune system indicators included the measurement of 

macrophage aggregates (MA) in preserved spleen and anterior kidney histology (Table 2). Macrophage aggregates, also 

known as melanomacrophage centers, are discrete aggregations of pigment-bearing macrophages found in the spleen, 

kidney, and sometimes liver of advanced teleosts (Agius, 

1980). These specialized cells are thought to be responsible 

for centralizing foreign material and debris for destruction, 

detoxification or reuse, storing waste products, contributing 

to the immune response, and storing/recycling Fe (Ellis and 

others, 1976; Ferguson, 1976). Although they may be affected 

by a variety of factors, MA measurements have responded 

to contaminant exposure in both field and laboratory studies 

(reviewed by Wolke (1992) and Blazer and others (1997)).

Measures of reproductive condition included plasma 

vitellogenin (vtg) concentrations, gonadosomatic index (GSI), 

and gonadal histopathology (Table 2). Although reproductive condition in fish can be influenced by many factors (for 
1

1

Table 3. Organochlorine chemical and elemental contaminants measured in whole body fish composite samples.—ContinuedContaminant Class and Analyte Chemical Name(s) or Atomic Symbol Principal Uses and Sources to Aquatic Ecosystems Organochlorine chemicals

p,p'-DDE 

p,p'-DDD (TDE) 

p,p'-DDT 

o,p'-DDE 

o,p'-DDD (TDE) 

o,p'-DDT

Total polychlorinated biphenyls (PCBs) Aldrin Dieldrin Endrin 

Heptachlor epoxide cis-Chlordane trans-Chlordane 

cis-Nonachlor 

trans-Nonachlor 

Oxychlordane (octachlor epoxide) 

HeptachlorMethoxychlor

2,2-bis (p-chlorophenyl)-1,1-dichloroethylene 

2,2-bis (p-chlorophenyl)-1,1-dichloroethane 

2,2-bis (p-chlorophenyl)-1,1,1-trichloroethane 

2-(o-chlorophenyl)-2-(p-chlorophenyl)-1,1-

dichloroethylene 

2-(o-chlorophenyl)-2-(p-chlorophenyl)-1,1-

dichloroethane 

2-(o-chlorophenyl)-2-(p-chlorophenyl)-1,1,1-

trichloroethane 

Mixture containing as many as 209 mono- through 

octa-chloro-substituted biphenyl congeners. 

1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro1,4:5,8-dimethanonaphthalene 

1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,8,8ahexahydro-1,4-endnnno-exo-5,8-dimethanonaphthalene 

1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8aoctahdyro-1,4- endo-endo-5,8-dimethanonaphthalene 

1,4,5,6,7,8,8-heptachloro-2,3-epoxy-3a,4,7,7atetrahydro-4,7-methano-1H-indene 

1,2,4,5,6,7,8,8-octachloro-2,3,3a,4,7,7a-hexahydro-4,7-

methano-1H-indene (1-α,2-α,3a-α,4-β,7-β,7a-α)

1,2,4,5,6,7,8,8-octachloro-2,3,3a,4,7,7a- hexahydro-4,7-

methano-1H-indene(1-α,2-β,3a-α,4-β, 7-β,7a-α)

1,2,3,4,5,6,7,8,8-nonachloro-2,3,3a,4,7,7a- hexahydro4,7-methano-1H-indene (1-α,2-α, 3-α, 3a-α, 4-β, 7-β, 

7a-α)

1,2,3,4,5,6,7,8,8-nonachloro-2,3,3a,4,7,7a- hexahydro4,7-methano-1H-indene(1-α,2-β,3-α, 3a-α,4-β,7-β,7aα)

2,3,4,5,6,6a,7,7-octachloro-1a,1b,5,5a,6, 6a-hexahydro2,5-methano-2H-indeno(1,2-b)oxirene (1a-α,1b-β,2-

α,5-α,5a-β,6-β,6a-α)

1H-1,4,5,6,7,8-8-heptachloro-3a,4,7,7a-tetrahydro-4,7-

methanoindene 

1,1’-(2,2,2-trichloroethylidene)-bis[4-methoxybenzene] 

DDT-metabolite

Insecticide; DDT-metabolite

Insecticide 

o,p'-DDT metabolite 

o,p'-DDT metabolite 

p,p'-DDT impurity Dielectric, hydraulic, and transformer fluids; lubricants; extenders; de-dusting agents; carbonless copy paperInsecticide Insecticide; aldrin metabolite

Insecticide; isodrin metaboliteHeptachlor metabolite; technical chlordaneconstituent/metaboliteInsecticide; technical chlordane constituent

Technical chlordane constituent

Technical chlordane constituent 

Technical chlordane constituent 

cis-Chlordane metabolite Insecticide 

Insecticide 

MaterialsandMethods
1

2

Table 3. Organochlorine chemical and elemental contaminants measured in whole body fish composite samples.—ContinuedContaminant Class and Analyte Chemical Name(s) or Atomic Symbol Principal Uses and Sources to Aquatic Ecosystems 

Toxaphene Chlorinated camphene mixture averaging 62% chlorine Insecticide; herbicide 

by weight 

α-Hexachlorocyclohexane (HCH) 1,2,3,4,5,6-hexachlorocyclohexane Constituent of insecticide mixture containing various HCH

isomers; also know as α-benzene hexachloride (BHC) 

β-HCH 1,2,3,4,5,6-hexachlorocyclohexane Technical HCH (BHC) constituentδ-HCH 1,2,3,4,5,6-hexachlorocyclohexane Technical HCH (BHC) constituentγ-HCH (Lindane) 1,2,3,4,5,6-hexachlorocyclohexane Insecticide; technical HCH (BHC) constituentHexachlorobenzene (HCB) Perchlorobenzene Fungicide; industrial intermediate Pentachlorobenzene Chlorinated benzene Fungicide; fire retardant

Pentachloroanisole Chlorinated benzene Fungicide; metabolite of chlorinated aromatic chemicalsEndosulfin I 6,9-methano-2,4,3-benzodioxathiepin,6,7,8,9,10,10- Pesticide 

hexachloro-1,5,5a,6,9,9a 

Endosulfin II 6,7,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9- Pesticide

methano-2,4,3-benzodiozathiepin-3-oxide, (3α, 5aα,

6β, 9β, 9aα)

Endosulfan sulfate 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9- Endosulfan byproduct 

methano,2,4,3-benodiatiepin 3,3-dioxide 

Mirex 1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodecachloro- octahydro- Insecticide; fire retardant 

1,3,4-metheno-1H-cyclobuta(cd)pentalene 

Elemental contaminants

Arsenic As Industrial sources; herbicides; defoliants Cadmium Cd Mining, smelting and other industrial sources; urban runoff; 

sewage discharges

Chromium Cr Mining, tanning, and other refractory and chemical industrial

sources

Copper Cu Mining, smelting and other industrial sources Lead Pb Mining, smelting and other industrial sources; urban runoff; 

atmospheric pollution; fishing sinkers; lead shot 

Mercury Hg Herbicides; fungicides; pulp, paper, and textile effluents;

open-cycle chloralkali cells; landfills; mining; atmosphericpollution

Nickel Ni Mining, smelting, and other industrial sourcesSelenium Se Coal-fired powerplants; irrigation return flows Zinc Zn Mining, smelting and other industrial sources; urban runoff 

EnvironmentalContaminantsandtheirEffectsonFish
Materials and Methods 13

Table 4. Monitoring and assessment strategy for Field Procedures

polycyclic aromatic and polyhalogenated 

hydrocarbons (PAHs and PHHs). a

Total PCBs were Teams of three to seven biologists collected and prodetermined by gas chromatography with electron- cessed the fish. The leader of each team (and other team 

capture detection. b

7-ethoxyresorufin O-deethylase. members) had participated in a training session to gain c

H4IIE bioassay was performed after reactive cleanup familiarity with collection, dissection, storage, handling, and 

to remove AhR-active PAHs. d

And other planar recording protocols. Sampling commenced in May 2002 and 

organic compounds. + responds; – does not respond; was completed in July 2002 with the exception of Station 305, 

*AhR-active isomers and congeners only. which was completed in early October 2002. Teams spent 2-5 

days at each station.

PAHs

GC-ECDa + - -

(carcass) Fish Collection

EROD * * * Fish were collected by angling, gill nets, and fyke nets. 

activityb Collection was generally conducted along the shoreline or 

(liver) backwater areas of the river being sampled. More than 10 fish 

H4IIE 

bioassayc 

(carcass) 

* * - of a given species and gender were collected at some sites if 

gender was not easily discernible in the field. Global Positioning System (GPS) coordinates were obtained at the upstream 

and downstream locations at the sampling site where fish were 

collected. Fish were held in live wells or tethered in the water, 

example gender, age, reproductive stage, season, water temperature), contaminants, particularly estrogen mimics, have 

transported to processing sites, and usually processed within a 

few hours of collection.

been shown to impact reproduction in laboratory and field 

studies (Allen and others, 1999; Gimeno and others, 1998). 

Estrogen mimics are capable of stimulating the production of Sample Processing

vtg, a precursor of yolk protein, in the livers of oviparous vertebrates. A number of endocrine-disrupting compounds have The methods used to process the fish have been fully 

been shown to induce abnormal vitellogenesis (Servos, 1999; described (Table 2; Schmitt and others, 1999a; Schmitt and 

Tyler and others, 1998). Vitellogenin production is normally Dethloff, 2000). Briefly, a live fish was selected and identified 

associated with female fish; however, it can be produced in to species. A blood sample was collected from the posterior 

males if estrogen or an estrogen-like chemical is present. The caudal artery and vein with a heparinized needle and syringe 

detection of levels typical of early- to mid-vitellogenic females and placed on wet ice. From this sample, plasma was later 

in male fish has been associated with exposure to exogenous obtained for determination of vtg and steroid hormone conestrogens (Bowman and others, 2002; Denslow and others, centrations. The fish was then weighed, measured, and killed. 

1999; Folmar and others, 1996; Folmar and others, 2000; Observations of external features were recorded, and tissue 

2001). To document these and other possible alterations and anomalies were removed by dissection and preserved in 10% 

to establish baseline concentrations, vtg was measured in both neutral buffered formalin (NBF) for histopathological analysis. 

male and female fish. GSI and gonadal histopathology (stage, The abdominal cavity of the fish was dissected open and the 

presence of atretic oocytes, and intersex conditions [presence liver (in species with a discrete liver), spleen, and gonads were 

of female reproductive tissue in males or vice versa]) were removed and weighed. Liver weights for longnose sucker 

also assessed as measures of reproductive health and status. were not determined because this species has a dispersed 

The GSI relates the proportional size of the gonad to the body hepatic organ. The liver, gall bladder, posterior and antesize and may reflect changes resulting from a variety of physi- rior kidneys, gonads, mesenteric fat (in certain species), and 

ological factors such as reproductive stage and environmental spleen were examined, and the gender of the fish was visually 

factors, including exposure to contaminants. Elevated occur- determined. Pieces of liver were collected and immediately 

rence of atretic (reabsorbed and/or degenerating) eggs has flash-frozen in liquid nitrogen dry shipper and remained there 

been noted in fish exposed to contaminants (Cross and Hose, until sample shipment; these samples were later analyzed 

1988; Johnson and others, 1988), although other factors may for EROD activity. Samples of gonad, kidney, spleen, and 

also be involved. Feminization of male fish (that is, intersex additional pieces of liver were collected and preserved in 10% 

condition) has been reported in laboratory and field studies NBF for histopathological examination, gender confirmation 

of contaminants (Allen and others, 1999; Gimeno and others, (gonad), and macrophage aggregate analysis (spleen). Upon 

1997; Gimeno and others, 1998; Jobling and others, 1998). completion of the internal examination and dissection, otoliths 

or scales were collected for age determination. Remaining 

Contaminants 

Endpoint PCBs 

PCDDs & 

PCDFs 

d 
14 Environmental Contaminants and their Effects on Fish

tissues (those not frozen or fixed) were placed back into the 

body cavity and the entire fish was wrapped in aluminum foil. 

The wrapped carcass was placed in a polyethylene bag with 

other carcasses of the same species and gender and labeled. 

These samples were chilled and later frozen for analysis of 

organochlorine chemical and elemental contaminants and 

dioxin-like activity (with the H4IIE bioassay). The entire field 

procedure was typically conducted in 15-20 min (per fish), and 

tissue samples, especially liver for EROD analysis, were collected and frozen as rapidly as possible. Blood samples were 

centrifuged and the plasma was aspirated and frozen in dry ice 

following the processing of the fish.

Laboratory Analysis

Composite fish samples were shipped frozen in dry ice 

to the Columbia Environmental Research Center (CERC) 

of the U.S. Geological Survey (USGS). CERC performed 

analyses of composite fish samples for organic and elemental contaminants and completed quality assurance (QA) and 

quality control (QC) procedures. Fish were composited, 

homogenized, and lyophilized by LET, Inc. (Columbia, MO) 

according to protocols given by CERC. Spike recoveries and 

moisture loss during storage were not reflected in the reported 

results. Cryogenically frozen liver samples for EROD analysis 

were also shipped (in liquid nitrogen dry shippers) to CERC 

for analysis. Cryogenically frozen plasma samples were 

similarly shipped to the Protein Chemistry Research Laboratory of the University of Florida for analysis of vtg and the 

Florida Integrated Science Center of the USGS for steroid 

hormones analysis. Preserved tissue samples were shipped to 

the Leetown Science Center (LSC) of the USGS and Northwest Fisheries Science Center of the National Oceanic and 

Atmosphereic Administration (NOAA) for histopathological 

analysis. Information on these latter procedures are given by 

Blazer and others (2002) and McDonald and others (2002). 

Otoliths were processed for age determination in northern pike 

following modified procedures from Chilton and Beamish 

(1982) and Haas and Recksiek (1995). Scales were processed 

for age determination as described by Jearld (1983), with age 

(years) estimated from the number of completed annuli when 

otoliths were not available.

Composite Sample Preparation

Carcass samples were shipped to and stored frozen (-20° 

C) at CERC. Individual fish carcasses were composited by 

gender and species and homogenized. One subsample (~100 

g) of the composite was refrozen for analysis of moisture content and the elemental contaminants, and a second sub-sample 

(~100 g) was refrozen for analysis of lipid content, organic 

contaminants, and the H4IIE bioassay. Details of these procedures are given in the following sections.

Elemental Contaminants and Moisture Content

For the determination of aluminum (Al), Ba, beryllium 

(Be), Cd, Cr, Cu, Fe, Pb, magnesium (Mg), Mn, molybdenum 

(Mo), Ni, strontium (Sr), vanadium (V), and Zn, digestates 

were prepared from whole body fish suitable for analysis by 

a semi-quantitative inductively coupled plasma mass spectrometry (ICP-MS) metals scan. A homogenized aliquant of 

each dried sample (~0.25 g) was heated with 6 mL of nitric 

acid in a sealed low-pressure Teflon® vessel in a microwave 

oven. The cooled digestate liquid was transferred to a 125 mL 

polyethylene bottle and ultrapure water (> 10 megOhm/cm) 

was added, yielding a final weight of 101.5 g (100 mL). The 

final acid matrix was 6% HNO . An additional tissue ali- 3

quant (~0.5 g) of each dried tissue sample was subjected to a 

magnesium nitrate–nitric acid dry ashing procedure followed 

by hydrochloric acid (HCl) reduction for the determination of 

As and Se. The dry ashing procedure consisted of three steps: 

1) boiling with nitric acid for solubilization and partial oxidation; 2) 500°C ashing with magnesium nitrate to complete the 

oxidation and decompose remaining organic matter; and 3) 

heating with HCl to dissolve the ash and reduce Se and Se+4

oxidation state required for hydride generation. Following 

the HCl reduction, digestates were diluted to ~100 mL with 

de-ionized water, which yielded a final acid matrix of 10% 

HCl. For the determination of Hg in fish samples, there was 

no chemical preparation (digestion) because the dried sample 

was thermally decomposed in the analysis.

Concentrations of Al, Ba, Be, Cd, Cr, Cu, Fe, Pb, Mg, 

Mn, Mo, Ni, Sr, V, and Zn were determined by ICP-MS using 

the semi-quantitative scan mode. All samples were diluted 

10X by a CETAC ASD-500 auto-diluter as part of the analytical sequence. Internal standards were germanium (Ge) (50 

ng/g), rhodium (Rh) (10 ng/g), and thorium (Th) (10 ng/g). 

The external standard consisted of a NIST traceable reference 

solution to which five elements (praseodymium (Pr), terbium 

(Tb), thulium (Tm), tantalum (Ta), and gold (Au)) were added 

for improved calibration in the rare earth region of the mass 

spectral range. Mercury was determined by thermal combustion amalgamation atomic absorption (AA) with a direct mercury analyzer (Milestone DMA-80). The determination of As 

and Se in dried ash samples was accomplished by flow injection hydride generation atomic absorption spectroscopy. The 

digestates were mixed with HCl carrier solution and reduced 

by sodium tetrahydridoborate which has been stabilized with 

sodium hydroxide. The resulting volatile hydrogen selenide 

or arsenide was transferred with argon carrier gas into a heated 

quartz cell mounted on an atomic absorption spectrophotometer for decomposition and measurement. 

Limits of detection (LODs) were determined individually 

for each sample but were nominally 0.026 μg/g dry weight 

(dw) for As, 0.013 μg/g dw for Se, and 0.002 μg/g dw for Hg. 

Most elemental concentrations determined with the semiquantitative scan ICP-MS were below the reporting limits. 

The LODs, as well as the analytical results, were converted 
Materials and Methods 15

to wet-weight (ww) concentrations for statistical analysis and 

reporting.

Organochlorine Contaminants and Lipid Content

Residues of organochlorine pesticides (OCs) and PCBs 

were measured in the YRB composite fish samples using trace 

organic analysis methods that included extracting and purifying the residues and was followed by quantification with high 

resolution capillary gas chromatography with electron capture 

detection. Targeted OCs included the following: pentachlorobenzene, hexachlorobenzene, pentachloroanisole, alpha-BHC, 

beta-BHC, lindane, delta-BHC, heptachlor, heptachlorepoxide, aldrin, dieldrin, endrin, oxychlordane, cis-chlordane, 

trans-chlordane, cis-nonachlor, trans-nonachlor, o,p’-DDE,

o,p’-DDD, o,p’-DDT, p,p’-DDE, p,p’-DDD, p,p’-DDT, endosulfan I and II, endosulfan sulfate, methoxychlor, mirex, and 

toxaphene (Table 3). PCB congeners comprising >95% of the 

PCB mass in the composite samples were individually quantified (n>140) and summed to attain a total PCB concentration. 

The PCB congeners as identified by the International Union of 

Pure and Applied Chemistry (IUPAC) included the following: 

001, 003, 004, 005, 006, 007, 008, 009, 010, 015, 016, 017, 

018, 019, 020, 022, 024, 025, 026, 027, 028, 031, 032, 033, 

034, 035, 037, 040, 041, 042, 043, 044, 045, 046, 047, 048, 

049, 051, 052, 053, 054, 055, 056, 059, 060, 063, 064, 066, 

067, 069, 070, 071, 072, 074, 075, 082, 083, 084, 085, 086, 

087, 090, 091, 092, 094, 095, 096, 097, 099, 101, 102, 105, 

109, 110, 114, 115, 117, 118, 119, 122, 123, 124, 128, 129, 

130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 141, 144, 

146, 147, 149, 151, 153, 156, 157, 158, 163, 164, 166, 167, 

170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 183, 

185, 187, 189, 190, 191, 193, 194, 195, 196, 197, 198, 199, 

200, 201, 202, 203, 204, 205, 206, 208, and 209.

The analytical procedure began with blending 100 g 

anhydrous sodium sulfate with a 25 g portion of composite 

sample. The targeted chemicals were then extracted from the 

dried sample with a 1-h soaking in glass columns and elution with dichloromethane. The extract was quantitatively 

split into the following portions: H4IIE bioassay (80%, 20 g 

equivalent of fish tissue); OC/PCB/toxaphene analyses (8%, 

2 g); percent-lipid determination (2%, 0.5 g); and archive 

(10%, 2.5 g). Percent lipid was measured gravimetrically after 

evaporation of the extraction solvent. Lipids were removed 

from the bioassay portions of the extract by digestion using 

acidic and basic reactive silica gels. The analytical portion of 

the extract was spiked with the following chemical standards 

to track method recoveries: PCB 029 (2,4,6-trichlorobiphenyl), PCB 155 (2,2’,4,4’,6,6’-hexachlorobiphenyl), PCB 204 

(2,2’,3,4,4’,5,6,6’-octachlorobiphenyl), tetrachloro-m-xylene, 

and dibutylchlorendate. PCB 029 is representative of more 

volatile early-eluting PCBs (Cl1 - Cl3); PCB 155 is representative of mid-range eluting congeners (Cl4

 - Cl6); and PCB 204 

is less volatile and representative of later-eluting PCBs (Cl7

- Cl10). Each of these standards was used to monitor recovery 

of their respective PCB ranges.

Method performance was monitored by quality control samples [triplicates, blank fish tissues (negative control 

bluegill (Lepomis macrochirus)), blank reagents (procedural 

blank), and spiked blank fish] included with each analytical 

sample batch. The spiked samples received a 1:1:1:1 ratio 

mixture of Aroclors 1242, 1248, 1254, 1260 (1000 ng/g fish 

tissue), the 27 OCs (each 20 ng/g fish tissue) that included a 

technical mix of toxaphene (50 ng/g fish tissue). Triplicate 

analyses of each YRB species (northern pike, longnose sucker, 

and burbot) were conducted.

The analytical portion of the extract was purified by 

removing interfering co-extracted lipids and biogenic materials prior to the gas chromatographic quantification of the 

targeted OCs. The bulk of the interferences were removed 

by low-pressure size-exclusion chromatography (LPSEC), 

specifically, a 90cm x 4cm SX-3 column with dichloromethane elution. High performance SEC (HPSEC) was used 

to remove residual interferences. A two-layered octadecyl 

silica/activated silica gel column was used to separate the OCs 

from the PCBs prior to gas chromatography (GC) analysis that 

produced two fractions: Fraction-1 (F1) containing PCBs with 

six OCs and Fraction-2 (F2) containing the remainder of the 

OCs.

Fraction-1 and F2 extracts were adjusted to final volumes 

of 2 mL, and PCB 030 and 207 were added as instrumental 

internal standards. Individual PCB congeners were measured 

in F1, and individual OC pesticides were measured in both 

fractions. Hewlett-Packard (HP) 5890 Series II Gas Chromatographs with cool on-column capillary injection systems 

and HP 7673 autosamplers were used. A 3-m section of 0.53 

mm i.d. uncoated deactivated capillary retention gap was 

attached by a Press-Tight union to each of the analytical columns that were 60 m x 0.25 mm x 0.25 μm DB-5 (5% phenyl-, 

95% methylsilicone) and DB-17 (50% phenyl-, 50% methylsilicone). The GC conditions for the PCB analysis were: H2

-

carrier gas regulated at 25 psi, initial temperature 60°C, immediately ramped to 150°C at 15°C/min, then ramped to 260°C 

at 1°C/min, and finally ramped to 300°C at 10°C/min, and 

held for 15 min; Electron Capture Detector (ECD) at 330°C. 

The capillary GC/ECD data were collected, archived in digital 

form, and processed using a Perkin-Elmer chromatography 

data system and version 6.2 of TotalChrom Workstation. The 

method detection limits (MDLs) for each targeted contaminant were based on procedural blank (PB) results following to 

the method described by Keith (1991). A mean and standard 

deviation (SD) are based on several years of PB results (n>10). 

This was used to produce a long-term MDL [MDL = meanPB 

+ 3(SDPB)] and a method quantitation limit [MQL = meanPB 

10(SD)PB)] (Childress and others, 1999). The precision of the 

methods and percent recoveries are presented in Appendix 1. 

PCB congeners were matched and identified on the 60-m 

DB-17 column, and the total PCB concentration was determined as a sum of congeners (>95% of the PCB mass). A 

mixture of several Aroclors was used to produce the PCB con-
16 Environmental Contaminants and their Effects on Fish

gener calibration standards. These standards were quantified 

based on primary PCB standards (Accustandard, New Haven, 

CT) and used as secondary standards. Up to nine levels of 

calibration for each individual congener were used to quantify 

the congeners in the YRB samples. The calibration curve for 

total PCB concentrations in the solutions ranged from 10 to 

8000 ng/mL (10 - 8000 ng/g ww). Dual-column data were 

used to confirm OC pesticide identities using different phases 

of GC columns to produce unique, complementary retention times. An OC retention time and quantity based on one 

column analysis was matched with retention time and quantity 

on the second column. The calibration ranged from 0.1 to 80 

ng/mL (0.1 - 80 ng/g ww).

Total toxaphene concentrations were determined in 

F2 on the 60-m DB-17 column by quantifying components 

that matched relative retention times of components of the 

technical 4-40 ng/g toxaphene standard. Concentrations 

of toxaphene in the YRB samples ranged from <11 ng/g 

to three times the MDL (34 ng/g). The pattern of the very 

small component peaks varied among samples. This variation among fish samples has been described previously in the 

arctic (Bidleman and others, 1993). The GC/ECD method met 

the data quality objectives set for this study and provided a 

sufficiently low LOD. However, there are other methods for 

determining concentrations of toxaphene <11 ng/g (Muir and 

de Boer, 1993).

H4IIE Rat Hepatoma Cell Bioassay

The subsamples for H4IIE analysis were kept frozen at 

CERC until sample processing. Full details of processing 

have been previously described (Schmitt and others, 2002a). 

Briefly, samples were thawed, homogenized, and extracted 

from a column with methylene chloride. Percent lipid was 

determined on a 1% portion of the extract. The remainder was 

concentrated and cleaned up by two-stage column chromatography. Extracts were evaporated, redissolved with isooctane 

and ampulated. Matrix QC of prepared samples (blanks and 

spikes) included ground tissues from laboratory-raised bluegill 

and samples of a CERC standard positive control tissue (common carp from Saginaw Bay, MI). These QC samples were 

processed concurrently with the YRB samples.

The H4IIE bioassay was performed on the extracts 

according to the method of Tillitt and others (1991). These 

samples were screened in the H4IIE bioassay to determine if 

a full dose assessment was required. The screening procedure 

dosed the extracted samples and QC concentrates in quadruplicate with no accompanying serial dilution, and the 2,3,7,8-

tetrachlorodibenzo-p-dioxin (TCDD) standard was dosed in a 

3-fold serial dilution.

The H4IIE rat hepatoma cells were seeded at 23,000 

cells/well in 300 μL of D-MEM culture media (Tillitt and others, 1991) and allowed to proliferate for 24 h. The cells were 

then dosed with sample extracts or standards in isooctane and 

incubated for 72 h to allow for maximal EROD induction. A 

standardized TCDD solution was used to generate an analytical dose-response curve. A total of five dose-response curves 

were analyzed on the assay date. A linear regression was performed on each sample well to obtain the slope and estimate 

the rate of the reaction (pmol/min). The amount of protein in 

each well was determined by the fluorescamine assay (Lorenzen and Kennedy, 1993) and the values used to normalize dose 

to each well and EROD activity. The reaction rate observed in 

each well was normalized according to the measured protein 

content, generating a value of specific activity (pmols resorufin formed/minute/mg of protein). The reaction rate in each 

well was then divided by the measured dose given to each well 

(gram equivalents/mg) to result in specific activity per min 

per gram equivalent (g.eq.) dosed. Reported results are the 

average of four replicate concentrate doses. The mean EROD 

reaction rate (pmol/min/g.eq.) was divided by the average 

initial slope obtained for the TCDD standard curves, resulting 

in a measure of an equivalent dose of TCDD (TCDD-EQ) for 

each sample.

EROD Activity

Cryogenically frozen liver samples were stored at –80°C 

until the preparation of microsomal fractions that were used 

the day they were prepared. The kinetic microsomal assays 

were conducted in 96-well microtiter plates (Hinck and others, 

2003; Whyte and others, 2000). Briefly, triplicate determinations of EROD activity were performed on 10-μL portions of 

each microsomal preparation, and mean EROD activity was 

reported. Protein content was determined using the fluorescamine protein assay (Lorenzen and Kennedy, 1993) in 

the same 96-well microtiter plate as the EROD analyses. A 

positive control material, liver microsomes from male Sprague 

Dawley rats injected with 500 mg/kg of Aroclor 1254, was 

also analyzed. A linear regression was performed on the 

data from each well to determine an EROD rate (pmol/min) 

along with its associated estimate of variance. The amount of 

protein was used to normalize EROD activity (pmol/min/mg) 

in each well. A rigorous QA program was followed for the 

EROD assays (Hinck and others, 2003). The LOD was calculated by adding the average basal EROD rate to three times 

the standard deviation of that rate, and the limit of quantification (LOQ) was calculated by adding the average basal EROD 

rate to ten times the standard deviation of that rate. LODs 

ranged from 0.16 to 0.70 pmol/min/mg whereas the LOQs 

ranged from 0.8 to 1.41 pmol/min/mg. The results of this QA 

program indicated that the results of the bioassay accurately 

reflected the hepatic EROD rates of the samples analyzed.
Materials and Methods 17

Fish Health Indicators

General Histopathological Analyses

Tissues preserved in 10% NBF (liver, kidney, spleen, gill, 

gonad, and grossly visible lesions) were shipped to the LSC 

(Leetown, West Virginia) and NOAA (Seattle, Washington) 

and prepared for routine histopathological analysis (Blazer and 

others, 2002). Tissue sections (6-μm, on glass slides) were 

stained with hematoxylin and eosin (H & E) for light microscopic examination.

Quantitative Organism-Level Indicators

The prevalence of gross external pathological disorders 

was determined with a rating of present (1) or not present (0) 

deduced from field data. Gross pathologies were selected for 

consistency with other monitoring programs that have used 

this type of assessment (Fournie and others, 1996). Gross 

abnormalities included grossly visible disorders of the eye 

(exopthalmia, hemorrhage, opacity, emboli, missing), opercles, (shortening, deformities, parasites), and body surface 

(ulcers, parasites, discolored areas or tumors). In addition, 

disorders of the fins and skeleton were included. Numerical 

values were assigned to internal and external observations of 

lesions recorded in the field, and a necropsy-based fish health 

assessment index (HAI) score was calculated for each fish by 

summing these values for all organs (Blazer and others, 2002). 

An index was computed for a fish only if there was a complete 

assessment.

Body and organ weights measured in the field were used 

to calculate condition and organosomatic indices. Condition factor was computed as body weight (g)/length3 (cm). 

The HSI was calculated as liver weight/(total body weight 

– gonad weight) X 100. Similarly, the SSI was calculated as 

spleen weight/(total body weight – gonad weight) X 100. The 

weight of the gonads was subtracted from the body weight 

in the computation of HSI and SSI to minimize the effect of 

the reproductive cycle on these indices (Dethloff and Schmitt, 

2000). GSI was calculated as gonad weight/total body weight 

X 100. Additional information on these indices is given by 

Blazer and others (2002) and Dethloff and Schmitt (2000).

Macrophage Aggregates

Macrophage aggregates and MA pigments in spleen 

sections were visualized through a staining procedure called 

the Perl’s method (Luna, 1992). Using this method, melanin, 

a melanosome pigment derived from tyrosine metabolism, 

appears black; hemosiderin, a protein-bound iron pigment, 

appears blue; and ceroid/lipofuscin, lipogenic pigments arising 

from the oxidation of unsaturated lipids, appears yellow-tan. 

All MA measurements were made with a computer-based 

image analysis system and included the number of aggregates in 2 mm2

 of tissue (MA-#) and the area of each aggregate (MA-size). The percentage of tissue occupied by MA 

(MA-%) was computed from these measurements (Blazer and 

others, 2002).

Reproductive Indicators

Gonadal Histopathology

The posterior tip of the gonad was dissected in the field 

and fixed immediately in 10% NBF. Transverse sections were 

processed for routine light microscopy (embedded in paraffin, 

sectioned at 6 μm, and stained with H & E).

Female gonadal tissue was staged using developmental 

stages (designated 0-5) to classify each section (Blazer, 2002; 

McDonald and others, 2002; Nagahama, 1983; Rodriguez and 

others, 1995; Treasurer and Holliday, 1981). Fish ovaries typically contain oocytes in several developmental stages and were 

classified according to the maturity of the predominant stage 

of oogenesis of each tissue samples (Fig. 2). Ovaries containing only undeveloped, previtellogenic oocytes were assigned 

to stage 0. Samples containing only previtellogenic chromatin nucleoli and perinuclear oocytes, identified by cytoplasm 

that stained basophilic with H & E were assigned to stage 1. 

Ovaries containing previtellogenic oocytes as in stage 1 plus 

some cortical alveoli oocytes were classified as stage 2 (early 

vitellogenic). Those containing larger oocytes in which the 

cortical alveoli were pushed to the periphery of the cell, yolk 

globules filled the center, and the chorion of the developing 

oocytes were thicker than in earlier stages were designated as 

stage 3 (mid-vitellogenic). Ovaries containing oocytes with 

fused yolk globules were designated as stage 4 (late vitellogenic). Ovaries containing postovulatory follicles, which 

can be observed for some time after ovulation, are typically 

assigned to stage 5 (spent). After the ovarian tissues were 

staged they were further examined by light microscopy for 

atresia (Fig. 2) and other abnormalities. One hundred oocytes 

in each sampled were counted, when possible, and those showing morphological evidence of resorption or necrosis were 

quantified and the percent of atretic oocytes were calculated.

Analogous to the procedure used to stage ovaries, male 

gonadal tissue was classified into five developmental stages 

(0-4) according to the maturity of the predominant stage of 

spermatogenesis of each tissue sample (Fig. 3; Blazer, 2002; 

Nagahama, 1983). Immature, undeveloped, or regressed 

testes containing only spermatogonia were classified as stage 

0 (immature) whereas those containing primarily spermatocytes and spermatids were designated as stage 1 (early 

spermatogenic). Stage-2 (mid-spermatogenic) testes contain 

approximately equal proportions of spermatocytes, spermatids, and spermatozoa, and testes containing primarily mature 
18 Environmental Contaminants and their Effects on Fish

Figure 2. Gonadal stages and atresia in female fish ovaries. A. Stage-1 (immature) ovary containing previtellogenic oocytes. B. Stage-2 

(early-vitellogenic) ovary containing oocytes with cortical alveoli (a). C. Stage-3 (mid-vitellogenic) ovary containing enlarged oocytes. 

Cortical alveoli (a) are migrating to periphery, and yolk globules (b) beginning to form. D. Stage-4 (late vitellogenic) ovary containing enlarged oocytes and condensed yolk globules. E. Stage-5 (spent) ovary containing postovulatory follicles (a) and previtellogenic 

oocytes. F. Atretic previtellogenic oocytes (a) where nucleus has begun to disintegrate, cytoplasm stains darker and abnormal cortical 

alveoli and yolk granules are present. H & E stain (X165).
Materials and Methods 19

Figure 3. Gonadal stages in male fish testes. A. Stage-0 (immature) testes having primarily spermatogonia. B. Stage-1 (early spermatogenic) testes having spermatogonia and spermatocytes present. C. Stage-2 (mid-spermatogenic) testes with approximately equal 

numbers of spermatocytes, spermatids, and spermatozoa. D. Stage-3 (late spermatogenic) testes containing primarily mature sperm. 

E. Stage-4 (spent) testes having residual sperm present. H & E stain (X412).
20 Environmental Contaminants and their Effects on Fish

spermatozoa were identified as stage 3 (late spermatogenic). 

Stage-4 testes are postspawning or spent. Testicular tissue was 

also examined microscopically for any abnormalities such as 

intersex and other abnormalities. Male fish were classified as 

intersex when individual or small foci of undeveloped oocytes 

were observed within testicular tissue (that is, when an ovotestis condition was detected).

Vitellogenin

Vitellogenin was purified from female northern pike and 

longnose sucker plasma samples using the BIOCAD purification system (Perseptive Biosystems) and anion exchange packing material (POROS 20HQ). Plasma was diluted 1:10 in 10 

mM bis-tris-propane, 150 mM NaCl, pH 9.0 and then loaded 

onto the ion exchange column. Nonbinding proteins were 

eluted by several column volumes of the dilution buffer. Vitellogenin is specifically released using a linear gradient of NaCl 

(150-800 mM), and captured using a fraction collector. The 

vtg protein peak was identified by comparing male, female, 

and estrogenized male chromatographs. After purification, 

the protease inhibitor, Aprotinin (10 KIU/mL), glycerol (50% 

v/v), and azide (0.02% v/v) were added. Total protein of vtg 

was determined by the Bradford assay using bovine albumin 

as a standard.

Purified vtg was screened for reactivity against a panel 

of anti-vtg monoclonal antibodies (Mabs) developed by the 

Biomarkers and Hybridoma Cores at the University of Florida/ 

Interdisciplinary Center for Biological Research (ICBR). 

Reactivity was determined by direct ELISA using purified vtg 

standards (0, 0.01, 0.1, 1.0 μg/mL) and male plasma. Mabs 

developed against carp (1C8, HL 1364) and white sucker 

(Catostomus commersoni; 2C11, HL 1689) vtg, reacted 

quantitatively to the vtg of northern pike and longnose sucker, 

respectively. Moreover, these antibodies did not recognize 

male plasma proteins.

Plasma vtg concentrations were determined by direct 

ELISA using monoclonal antibodies, 1C8 (HL 1364) for 

northern pike and 2C11 (HL 1689) for longnose sucker. The 

plasma samples were diluted 1:200, 1:10,000, 1:100,000 and 

1:1,000,000 with 10 mM phosphate, 150 mM NaCl, 0.02% 

azide, 10 KIU/mL Aprotinin, pH 7.6 (PBSZ-AP). Vitellogenin standards containing 1:200, 10 k, 100 k, and 1000 k 

male plasma (in PBSZ-AP) were added to account for matrix 

effect (Denslow and others, 1999). Samples and standards 

were loaded onto a 96-well ELISA plate (NUNC) in triplicate 

and stored overnight at 4oC in a humidified container. The 

following day the plates were washed four times with PBSZ 

and then blocked with 1% BSA in 10 mM tris, 150 mM NaCl, 

0.05% tween, 0.02% azide, 10 KIU/mL Aprotinin, pH 7.6 (1% 

BSA /TBSTZ-AP) for 2 h at room temperature. The plates 

were rewashed with PBSZ (four times) and the monoclonal 

and loaded to each plate. The lowest dilution (1:200) was 

probed with 3 μg/mL of the Mab and dilutions of ≥10,000 

with 1.0 μg/mL. After the addition of the Mab, plates were 

stored at 4oC overnight in a humidified container. The following day the plates were washed and the biotinylated secondary antibody (goat antimouse IgG-biotin) was added to each 

well at 1:1000 dilution in 1% BSA/TBSTZ-AP and incubated 

at room temperature for 2 h. The plates were washed, and 

strepavidin-alkaline phosphatase was added at 1:1000 dilution 

in 1% BSA/TBSTZ-AP and incubated for 2 h at room temperature. After washing the plates for the final time, the color 

was developed by adding 1mg/mL p-nitro-phenyl phosphate 

in carbonate buffer (0.03 M carbonate, 2 mM MgCl2, pH 9.6) 

and measuring the color using an ELISA plate reader (SpectraMax Plus384) at 405 nm. Curve fitting and data analysis were 

determined using SoftMaxProTM ELISA software (Molecular 

Devices).

ELISA sensitivity or LOD was 0.001 mg/mL for both 

species. The coefficient of variation (CV) of triplicate values 

and correlation coefficient were maintained at <10% and >

95%, respectively, to maintain ELISA accuracy. The outlier 

was removed if the CV triplicates were >10%, and the sample 

was run again. Inter- and intra-assay variation of this type of 

ELISA are typically, <10% and <5%, respectively.

Steroid Hormones

Concentrations of estradiol (E2) and 11-ketotestosterone (KT) in plasma samples collected from northern pike 

and longnose sucker were measured by radioimmunoassay 

(RIA). For analysis, samples were thawed and split. Duplicate plasma samples (50 μL) were extracted twice by adding 

4 mL of ethyl ether, vortexing for 1 min, freezing the aqueous 

layer in a methanol-dry ice bath, and decanting the ether layer 

containing the lipophilic sex steroids. Standard curves were 

prepared in phosphate-buffered saline with gelatin and azide 

(PBSGA) buffer using variable amounts of unlabeled E2 or 

KT (1, 5, 10, 25, 50, 100, 250, 500 and 1000 pg) and a constant concentration of radiolabeled hormone. Cross-reactivities of the E2 antiserum were examined against other steroids, 

including estrone, estriol, 17α-estradiol, and androstenedione 

and were found to be at acceptable levels. Cross-reactivities 

of the KT antiserum were examined against other steroids, 

including testosterone, dihydrotestosterone, and androstenedione and were also found to be at acceptable levels. Reaction 

comprised plasma extract (50 μL), radiolabeled sex steroid 

hormone (100 μL), and corresponding sex steroid hormonespecific antibody (100 μL) in PBSGA buffer (250 μL). The 

reaction solutions were allowed to equilibrate overnight, during which time the unlabeled hormone from the extract and a 

constant concentration of the corresponding radiolabeled sex 

steroid hormone competed for the same antibody binding sites. 

Following incubation, nonantibody-bound radiolabeled hormone was removed by adding 250 μL of charcoal dextran and 

centrifuging at 3000 X g for 10 min. Supernatant aliquots (0.4 

mL), containing bound radiolabeled hormone, were carefully 

removed, so as not to disturb the charcoal pellet, and placed 

in a vial with 4 mL of scintillation fluid. Radioactivity was 
Materials and Methods 21

measured using scintillation spectrophotometry. Sex steroid 

concentrations in plasma extracts were determined using a 

four-parameter logistics regression analysis of standard curves, 

which was then used to calculate concentrations for plasma 

extracts.

Hormone concentrations in plasma samples from northern pike and longnose sucker were corrected for extraction 

efficiency of 94 ± 3.4% for E2 and 89 ± 4.1% for KT. The 

minimum concentration distinguishable from zero was 7.4 pg/

mL for E2 and 9.7 pg/mL for KT. Pooled samples in triplicate 

were assayed serially in 10-, 20-, 30-, 40-, and 50-μL volumes 

(final volume of 50 μL with charcoal-stripped plasma). The 

resulting inhibition curves were parallel to the respective standard curve; the tests for homogeneity of regression indicated 

that the curves did not differ. Further characterization of the 

assays involved measurement of known amounts (1, 2, 5, 10, 

25, 50, 100, 250, and 500 pg) of E2 or KT in 50 μL charcoalstripped plasma. Inter- and intra-assay coefficients of variation were 8.3% and 9.5%, respectively, for E2 and 7.4% and 

8.9%, respectively, for KT.

The ratio of E2 to KT (E/KT) is an additional variable used to analyze sex steroids (Folmar and others, 1996; 

Hileman, 1994). Typically, female fish will have an E/KT 

ratio greater than 1.0, and male fish will have an E/KT ratio 

below 1.0, although exact ranges of normality and seasonal 

fluctuations in this variable have not been established. 

Data Set Composition and Statistical Analyses

For indicators based on individual fish (that is, biomarkers and demographic endpoints), data were discussed in terms 

of the magnitudes of the means or medians for combined 

stages or each stage within a gender for different species. 

Data were summarized graphically with box plots presenting 

the mean, median, range, and 25th and 75th percentiles. Some 

biomarkers were also analyzed more rigorously (see following 

sections).

Descriptive statistics were calculated for length, weight, 

and age data for species at individual stations. Fish for which 

no otoliths or only regenerated scales were collected (17 fish: 

16 northern pike; 1 longnose sucker) were not included in the 

presentation or analysis of age data. Fish for which the field 

gender identification could not be verified histologically (1 

northern pike and 1 longnose sucker) were reported as NG (no 

gonad). Data for northern pike, longnose sucker, and burbot are presented in tabular form and are discussed. Length 

and weights of northern pike were also analyzed statistically 

because of the influence of fish size on concentrations of Hg 

in predatory fish (see next section). Length and weight data 

for all other species are presented only in tabular form.

A total of 31 composite samples from 10 stations were 

analyzed for chemical contaminants in fish tissue. Nineteen 

samples (61%) from 10 stations were northern pike, nine 

samples (29%) from 5 stations were longnose sucker, and 

three samples (10%) from two stations were burbot. All 

results for composite samples were converted to, analyzed 

statistically as, and reported as ww concentrations. A value of 

one-half the LOD was substituted for censored values (that is, 

values <LOD) in the computation of un-weighted geometric 

station means and for statistical analyses and were substituted 

for censored values in all graphs (Schmitt and others, 1999b). 

Concentrations of many contaminants in 2002 YRB composite samples were <LOD, which precluded rigorous statistical 

analysis. Data for composite samples (tissue concentrations) 

are presented graphically and as tabular summaries. Geographic differences for Hg and Se were also examined statistically using analysis of variance (ANOVA). Log-transformed 

concentrations of these analytes in northern pike and longnose 

sucker were analyzed with series of t-tests using a pooled 

error mean-square (MSe) representing differences between 

or among samples of the same species from the same station. 

A nominal α-level of 0.01 was used in these comparisons to 

protect against experiment-wise error. Because concentrations 

of Hg in predatory fish increase with size, age, or both (for 

example, Wiener and others, 2002), log-transformed lengthadjusted (HgL) and weight-adjusted (HgW) concentrations 

were also tested using this procedure. Following the method 

of Brumbaugh and others (2001), the adjusted Hg values were 

computed by dividing the measured concentration in each 

composite sample by the mean length (m) and weight (kg) of 

the individual fish comprised by the sample. Length, weight, 

Hg, HgW, and HgL were also analyzed separately for northern 

pike using the one-way analysis, which resulted in a more conservative test with fewer degrees of freedom and MSe

-values 

based on only one species. Chemical concentration data from 

other studies were compared to 2002 concentrations in the 

current report by converting dw concentrations to ww concentrations, assuming 75% moisture if the original study reported 

concentrations in dw and percent moisture was not reported.

Many biomarkers differ among species, gender, and 

reproductive stages (Schmitt, 2002a; Schmitt and Dethloff, 

2000). Accordingly, a series of linear ANOVA models were 

fit to the individual fish data for longnose sucker and northern pike to determine which factors influenced biomarker 

responses in these taxa, using the analyses conducted on larger 

previous BEST LRMN data set as a guide (Schmitt, 2002a). 

The results of these analyses were reported as F-values and 

significance levels and were used to guide the graphical presentation and discussion of the findings; however, because of 

the complexity of the models and the small size of the data set, 

the means could not be adjusted for the factors in the models. 

Data are presented and discussed in terms of the magnitudes 

of the means or medians for combined genders or each gender 

within a species and at different stations within a species. 

Some individual points are also discussed. Data are presented 

graphically and summarized as described for the demographic 

data.
22 Environmental Contaminants and their Effects on Fish

Results and Discussion

Geographic Distribution and Demographic

Characteristics of the Fish Collected

A total of 217 fish representing three species were collected from 10 YRB stations in 2002 (Table 5). Northern pike 

and longnose sucker accounted for 94% of the fish collected. 

Northern pike (n=158) were collected at 10 stations, longnose 

sucker (n=46) were collected at 5 stations, and burbot (n=13) 

were collected at 2 stations. Reasonable sample sizes (n>5) 

were obtained from seven stations for northern pike (Stations 

302, 303, 306, 307, 308, 309, and 310) and three stations for 

longnose sucker (Stations 301, 305, and 308) (Table 5).

Total length, weight, and age were examined in northern 

pike from the YRB. The mean total length (TL) of northern 

pike was 601 mm (range 373-1,085 mm) and mean weight was 

1,462 g (range 280-8,000 g) (Table 6). The mean age for all 

northern pike collected was 5.8 y (range 1-17 y). In general, 

female northern pike had a greater mass (623 g vs. 574 g) and 

were longer (1,643 mm vs. 1,246 mm) than male northern 

pike, but females were slightly younger (5.8 y vs. 5.9 y) than 

males. Male and female northern pike were generally smallest 

(mean TL and weight) at Station 303 (Table 6) and largest at 

Stations 306 and 307. Mean age for females and males was 

lowest at Station 303 and highest at Station 309 for females 

and Station 307 for males. Mean age was not consistently 

related to mean size; that is, the oldest northern pike were not 

necessarily the largest, which indicates that growth rates vary 

among stations (Table 6).

Total length, weight, and age were similar in longnose 

sucker sampled throughout the YRB. The mean TL and 

mass of longnose sucker from the YRB was 433 mm (range 

358-509 mm) and 674 g (range 350-1,250 g), respectively 

(Table 7). The mean age for longnose sucker was 2.9 y (range 

1-5). Female longnose sucker had a greater mass (449 g vs. 

399 g) and were longer (755 mm vs. 508 mm) than male 

longnose sucker, but the mean age for both female and male 

Table 5. Number of fish collected, organized by species, station, and gender, 

in the Yukon River Basin in 2002. Stations are listed upstream to downstream. 

Station numbers are given in parentheses. Species totals that include 

individual(s) of unknown gender are designated by an asterisk (*). 

Station and Species 

Charley-Kandik, AK (301) 18 

Northern pike 2 4 6 

Longnose sucker 1 11 12 

Fish Hook Bend, AK (302) 20 

Northern pike 5 15 20 

Fort Yukon, AK (303) 22 

Northern pike 11 11 22 

The Bridge, AK (304) 11 

Northern pike 2 7 9 

Longnose sucker 0 2 2 

Fairbanks, AK (305) 36 

Northern pike 0 3 3 

Longnose sucker 11 9 21* 

Burbot 4 8 12 

Tolovana, AK (306) 23 

Northern pike 10 10 20 

Longnose sucker 1 2 3 

Tanana, AK (307) 20 

Northern pike 8 12 20 

Galena, AK (308) 28 

Northern pike 12 8 20 

Longnose sucker 1 7 8 

Innoko, AK (309) 21 

Northern pike 11 9 21* 

Kotlik, AK (310) 18 

Northern pike 8 9 17 

Burbot 1 0 1 

Female 

Species 

Total Total 

Station 

Male 
Results and Discussion 23

Table 6. Lengths, weights, and ages of northern pike (Esox lucius) collected in the Yukon River Basin in 2002. Stations are listed 

upstream to downstream. Station numbers are given in parentheses. Sample size (n), arithmetic mean, standard deviation (SD), 

and range are also given. Fish for which gender could not be determined are identified as having no gonad (NG). 

Location Gender 

n Range 

Length (mm) 

Mean SD n Range Range 

Weight (g) 

Mean SD 

Age (years) 

n Mean SD

Entire Basin All 157 601 120 373-1085 158 1462 1125 280-8000 142 5.8 2.9 1-17 

F 88 623 135 373-1085 88 1643 1347 280-8000 77 5.8 2.8 2-17 

M 68 574 89 407-849 69 1246 702 310-3900 64 5.9 3.1 1-15 

NG 1 431 -- -- 1 430 -- -- 1 4 -- --

Charley- F 4 639 79 538-729 4 1553 561 852-2022 4 5.8 1.0 5-7 

Kandik, AK M 2 654 35 629-678 2 1568 286 1366-1770 2 8.5 2.1 7-10 

(301) 

Fish Hook F 15 608 80 460-757 15 1295 516 600-2600 13 5.8 1.9 2-9 

Bend, AK M 5 591 46 545-652 5 1162 355 800-1600 4 6.0 0.8 5-7 

(302) 

Fort Yukon F 11 537 83 374-654 11 829 319 280-1270 8 4.5 1.9 2-7 

AK (303) M 11 498 50 407-576 11 646 201 310-990 9 4.2 1.5 2-6 

The Bridge, F 7 725 250 415-1070 7 2923 2794 390-8000 6 7.0 2.8 3-10 

AK (304) M 2 579 141 479-678 2 1200 877 580-1820 2 6.0 4.2 3-9 

Fairbanks, F 3 615 74 568-700 3 1440 859 850-2426 3 5 1.7 4-7 

AK (305) M 0 -- -- -- 0 -- -- -- 0 -- -- --

Tolovana, F 10 661 158 545-1085 10 2061 2078 950-7820 8 6.3 4.9 2-17 

AK (306) M 10 609 99 450-720 10 1479 692 565-2460 10 5.7 4.1 1-12 

Tanana, AK F 12 615 148 373-865 12 1704 1001 300-3900 12 6.3 3.0 2-12 

(307) M 8 642 144 429-849 8 2069 1298 550-3900 8 8.9 4.3 3-15 

Galena, AK F 8 629 66 551-772 8 1525 452 950-2100 7 4.9 1.6 3-8 

(308) M 12 591 42 490-653 12 1325 256 800-1750 12 4.9 1.6 3-8 

Innoko, AK F 9 665 188 426-866 9 2163 1716 355-4658 8 7.5 2.9 3-11 

(309) M 10 521 76 442-650 11 945 553 430-1870 10 6.7 2.9 4-13 

NG 1 431 -- -- 1 430 -- -- 1 4.0 -- --

Kotlik, AK F 9 588 67 529-752 9 1372 348 950-3030 8 4.6 2.7 2-11 

(310) M 8 581 54 522-674 8 1236 306 880-1810 7 4.6 2.2 2-8 

longnose sucker was similar (2.9 y vs. 2.7 y). Mean size (TL and age varied more at some stations than at others, although 

and weight) and age of longnose sucker were similar among consistent patterns were not reflected in multiple species from 

stations (Table 7). Overall, the average lengths and weights of a station. Few relatively large or small individual fish conlongnose sucker from the YRB were similar but were younger tributed to this variation, and some degree of variation among 

than those collected from the CRB in 1997 (Hinck and others, stations was expected because sample sizes varied.

2004).

Burbot were collected from Stations 305 and 310. 

Female burbot outweighed male burbot (700 g vs. 589 g), 

were longer (2,387 mm vs. 1,100 mm), and were older (10.6 y 

vs. 9.5 y) at Station 305 (Table 7). Only one male burbot was 

collected from Station 310.

Fish collected from the YRB were relatively consistent 

among stations with respect to species, size, and age. Differences were noted among stations means for measured morphologic and demographic parameters of each species. Fish size 
24 Environmental Contaminants and their Effects on Fish

Table 7. Lengths, weights, and ages of longnose sucker (Catostomus catostomus) and burbot (Lota lota) collected in the 

Yukon River Basin in 2002. Stations are listed upstream to downstream. Station numbers are given in parentheses. Sample 

size (n), arithmetic mean, standard deviation (SD), and range are also given. Fish for which gender could not be determined 

are identified as having no gonad (NG). 

Location G

n 

ender 

Length (mm) 

Mean SD Range Range 

Weight (g) 

n Mean SD Range 

Age (years) 

n Mean SD

Longnose sucker 

Entire Basin All 46 433 40 358-509 46 674 204 350-1250 45 2.9 0.8 1-5 

F 31 449 37 366-509 31 755 196 405-1250 31 2.9 0.9 1-5 

M 14 399 22 358-435 14 508 85 350-700 13 2.7 0.5 2-3 

NG 1 400 -- -- 1 485 -- -- 1 4.0 -- --

Charley- F 11 456 25 424-491 11 738 135 527-946 11 3.4 0.5 3-4 

Kandik, AK M 1 435 -- -- 1 540 -- -- 1 3.0 -- --

(301) 

The Bridge, F 2 474 50 439-509 2 930 269 740-1120 2 3.5 0.7 3-4 

AK (304) M 0 -- -- -- 0 -- -- -- 0 -- -- --

Fairbanks, F 9 434 44 366-476 9 672 192 405-985 9 2.4 0.5 2-3 

AK (305) M 11 395 21 358-419 11 488 72 350-570 10 2.7 0.5 2-3 

NG 1 400 -- -- 1 485 -- -- 1 4.0 -- --

Tolovana, F 2 425 64 379-470 2 550 141 450-650 2 4.0 1.4 3-5 

AK (306) M 1 394 -- -- 1 500 -- -- 1 3.0 -- --

Galena, AK F 7 457 34 399-496 7 900 192 700-1250 7 2.4 1.0 1-4 

(308) M 1 415 -- -- 1 700 -- -- 1 2.0 -- --

Burbot 

Fairbanks, F 8 700 176 456-944 8 2387 1893 515-6312 8 10.6 3.1 5-14 

AK (305) M 4 589 129 496-755 4 1100 600 715-1988 4 9.5 4.2 5-14 

Kotlik, AK F 0 -- -- -- 0 -- -- -- 0 -- -- --

(310) M 1 565 -- -- 1 1080 -- -- 1 7 -- --

Accumulative contaminants, H4IIE Bioassay, 305 (Fairbanks) did not exceed 0.4 μg/g ww of As from 1972 

and EROD Activity to 1986 (Schmitt and others, 1999b); however, concentrations 

of As >0.4 μg/g ww were detected in burbot from Station 305 

in 2002. Most northern pike and longnose sucker collected 

throughout the YRB had concentrations of As (0.2 μg/g ww)

Elemental Contaminants similar to those found at the NCBP site from 1980 to 1986. A 

single northern pike from the MRB near Garrison Dam, North 

Dakota had a concentration of As <0.16 μg/g ww (Schmitt and 

Arsenic others, 2002a). Northern pike collected near Alamosa, Colorado in the RGB had concentrations <0.11 μg/g ww (Schmitt 

Arsenic was detected in all 31 composite samples at and others, 2004). Other studies measuring whole body conconcentrations ranging from 0.03 to 1.95 μg/g ww, with the centrations of As in northern pike, longnose sucker, or burbot 

maximum concentrations measured in male burbot from Sta- from the YRB were not found. Arsenic was not detected in 

tion 310 (Fig. 4; Table 8). All other concentrations of As were northern pike muscle samples from the Koyukuk and Innoko 

<1.08 μg/g ww with burbot samples having the three of the NWRs in 1988 (Snyder-Conn and others, 1992). Mueller and 

four greatest concentrations (>0.45 μg/g ww) (Fig. 4). The Matz (2002) reported concentrations of As ranging from 0.02 

greatest geometric station mean for As was in fish samples to 0.23 μg/g ww in northern pike muscle samples collected 

from Station 304 (0.44 μg/g ww) (Table 9). from the Innoko NWR in the YRB in 1996-1997. Ecosystem 

Concentrations of As from the YRB in 2002 were and hydrologic differences among stations may partly explain 

compared to previous studies in the basin. Fish composite the varying concentrations in burbot compared to northern 

concentrations from the NCBP station located near Station pike and longnose sucker from the YRB. Deschu (1985) 
Results and Discussion 25

μg/g μg/g

3

2

1

0

1

0.75

0.5

0.25

0

301 302 303 304 305 306 307 308 309 310

Northern pike 

Longnose sucker 

Burbot 

As 

Se 

Station 

Figure 4. Concentrations (μg/g ww) of arsenic (As) and selenium 

(Se) by station and species in whole body fish composite samples 

collected in the Yukon River Basin in 2002. Censored values are 

plotted as one-half the LOD. Stations are ordered upstream to 

downstream. See Table 1 for station descriptions.

determined background concentrations of As to range from 0.2 

to 0.5 μg/g ww in resident fish in Kantishna Hills, located in 

Denali National Park, south of the YRB.

Concentrations of As in northern pike, longnose sucker, 

and burbot were compared to those from wildlife criteria and 

laboratory toxicity tests. The concentrations of As detected 

in fish collected from the YRB in 2002 (0.03–1.95 μg/g ww) 

are not considered a hazard to the fish or to piscivorous fishes 

or wildlife (USEPA, 1984). Jarvinen and Ankley (1999) 

reviewed several laboratory studies in which effects of As 

were evaluated relative to whole body concentrations in fish. 

Concentrations of 8.1-13.5 μg/g ww were associated with loss 

of equilibrium and 5.4 μg/g ww caused increased mortality in 

rainbow trout (O. mykiss) fingerlings (McGreachy and Dixon, 

1990; 1992). Adult bluegill experienced reduced survival and 

growth at 11.6 μg/g ww (Gilderhus, 1966). Concentrations in 

all fish from the YRB were less than these effect levels.

Selenium

Selenium was detected in all composite samples (>0.2 

μg/g ww), with the maximum concentration measured in male 

burbot from Station 305 (Fig. 4; Table 8). Selenium concentrations ranged from 0.23 to 0.85 μg/g ww with concentrations

≥0.6 μg/g ww in samples from Stations 301, 302, 304, and 

305 (Fig. 4). Concentrations of Se did not reflect a pattern 

among species; northern pike, longnose sucker, and burbot 

all had concentrations ≥0.6 μg/g ww (Fig. 4). The geometric 

mean for Se was greatest in fish at Station 302 (0.72 μg/g ww) 

and lowest in fish at Stations 309 and 310 (Table 9). Amongstation differences for concentrations of Se were significant 

in northern pike but not in longnose sucker or burbot (Table 

10). Concentrations of Se in northern pike were significantly 

lower at Stations 309 and 310 compared to other YRB stations (Table 10; Fig. 4). Northern pike from Station 302 had 

concentrations of Se significantly greater than most stations, 

resulting in a decreasing Se trend upstream to downstream in 

the YRB.

BEST 2002 Yukon concentrations were compared to 

historical data from the YRB. Concentrations of Se from 

Station 305 were greater than NCBP concentrations near 

Fairbanks, which ranged from 0.30 to 0.58 μg/g ww for 

northern pike, longnose sucker, and burbot from 1972 to 1986 

(Schmitt and others, 1999b). Whole body concentrations of 

Se in northern pike were measured in the MRB near Garrison 

Dam, North Dakota (0.49 μg/g ww; n=1) in 1995 (Schmitt 

and others, 2002a) and RGB near Alamosa, Colorado (0.17-

0.69; n=4) in 1997 (Schmitt and others, 2004). Other studies 

measuring whole body concentrations of Se in these species 

in the YRB were not found. The USFWS has sampled fish 

from multiple NWRs in the YRB. Concentrations of Se were 

measured in northern pike muscle samples from the Koyukuk 

NWR (0.11-0.48 μg/g ww) and Innoko NWR (<0.11-0.21 

μg/g ww) in 1988 (Snyder-Conn and others, 1992). Concentrations of Se ranged from 0.14 to 0.44 μg/g ww in northern 

pike muscle samples from the Koyukuk, Innoko, and Nowitna 

NWRs in 1991 (Mueller and others, 1996). Northern pike 

muscle samples from the Innoko NWR had concentrations of 

Se ranging from 0.15 to 0.48 μg/g ww in 1996-1997 (Mueller and Matz, 2002). The NCP determined that northern pike 

muscle samples from the Yukon Territory within the YRB had 

concentrations of Se of 0.4-0.7 μg/g ww from 1996 to 2000 

(NCP, 2003).

Concentrations of Se were compared to those of laboratory toxicity tests and wildlife guidelines. Multiple studies 

have concluded bioaccumulation in the food chain is the 

primary source of Se toxicity to fish (see review by Hamilton, 2004). Several Se studies were included in a review 

by Jarvinen and Ankley (1999) on the effects of inorganic 

chemicals to aquatic organisms. Various studies from this 

review showed that whole body concentrations of Se between 

8 and 16 μg/g dw have led to reproductive failure in fathead 

minnows (Pimephales promelas) (Schultz and Hermanutz, 

1990) and bluegill (Coyle and others, 1993; Gillespie and 
26 Environmental Contaminants and their Effects on Fish

Table 8. Percent of samples and stations that exceeded limit of detection (LOD) concentrations for elemental 

contaminants in composite samples of whole fish from the Yukon River Basin in 2002. The maximum concentrations 

and associated sample information (station, gender, and species) from this study are also given. NA, not applicable. 

Analyte (

S

%

am

o

p

f 

l

3

e

1

s

) (μg/g) 

Maximum 2002 Concentration

Station Gender Species 

Stations 

(% of 10) 

LOD Range 

(μg/g) 

Arsenic 100 100 NA 1.95 Kotlik (310) M Burbot 

Charley-Kandik Cadmium 29 50 0.020-0.027 0.12 (301) F Longnose sucker 

Charley-Kandik Chromium 84 100 0.215-0.256 1.64 (301) F Longnose sucker 

Charley-Kandik Copper 100 100 NA 1.49 (301) F Longnose sucker 

Lead 0 0 0.205-0.273 NA NA NA NA 

Mercury 100 100 NA 0.65 Tolovana (306) F Northern pike 

Nickel 10 30 0.205-0.273 0.71 Charley-Kandik F Longnose sucker (301) 

Selenium 100 100 NA 0.85 Fairbanks (305) M Burbot 

Zinc 100 100 NA 56 Innoko (309) F Northern pike 

Baumann, 1986; Hermanutz and others, 1992). Another study 

concluded Se residues present in the egg stage or at hatch 

likely affects larval survival (Coyle and others, 1993). These 

results indicate that it is essential to examine multiple life 

stages to correctly assess toxicity/tissue concentration relationships (Jarvinen and Ankley, 1999). In addition, Se toxicity has 

been correlated with various conditions including swelling of 

gill lamellae, elevated lymphocyte count, anemia, corneal cataracts, exopthlamus, pathological alterations of liver, kidney, 

heart, and ovary, reproductive failure, and teratogenic deformities of spine, head, mouth, and fins (Hamilton, 2004; Lemly, 

2002). Whole body concentrations of Se should not exceed 

4 μg/g dw (0.8 μg/g ww assuming 80% moisture) to avoid 

toxicity to the fish and 3 μg/g dw (0.6 μg/g ww assuming 80% 

moisture) to avoid toxicity to piscivorous wildlife according 

to Lemly (1996) and other studies (see review by Hamilton, 

2004). Northern pike from Stations 301 and 302, longnose 

sucker from Stations 301, 304, and 305, and burbot from Station 305 exceeded either one or both thresholds. Therefore, 

concentrations of Se are of concern at some YRB stations. 

Mercury

Mercury was detected (>0.01 μg/g ww) in all composite 

samples, with the maximum (0.65 μg/g ww) concentration 

measured in female northern pike from Station 306 (Table 8). 

Concentrations of Hg were greatest in predatory fishes and 

were >0.3 μg/g ww in samples from Stations 304, 305, 306, 

307, and 308 (Fig. 5). The geometric mean was greatest in 

fish from Station 304 (0.41 μg/g ww) followed by Stations 307 

(0.39 μg/g ww) and 306 (0.36 μg/g ww) (Table 9). Amongstation differences for concentrations of Hg were significant in 

northern pike but not in longnose sucker or burbot (Table 10). 

Concentrations of Hg were significantly greater in northern 

pike from Station 304 compared to Station 310 (Table 10).

Predatory fish (northern pike, burbot) tend to accumulate greater concentrations of Hg than forager fish (longnose 

sucker) (Fig. 5; Schmitt and others, 1999b), and concentrations in predatory fish increase with size (that is, heavier and 

longer fish have greater concentrations of Hg). Therefore, it 

becomes necessary to examine concentrations of Hg adjusted 

for weight and length. However, it is difficult to relate the 

concentrations of Hg in composite samples to individual 

length and weight measurements, but overall trends or patterns 

can be identified. Concentrations of Hg were different than 

length- and weight- adjusted concentrations (HgL and HgW, 

respectively) although changes were not consistent among species (Fig. 5). In general, concentrations of HgW were lower 

and concentrations of HgL were greater in northern pike compared to unadjusted concentrations (Fig. 5). The HgW model 

did not indicate any spatial differences in Hg for northern pike 

(Table 10) and would indicate this model did not accurately 

describe concentrations of Hg. However, the HgL model 

showed similar results but had greater mean concentrations 

at all stations compared to concentrations in the unadjusted 

model in terms of spatial differences. For example, concentrations of Hg were significantly less in northern pike from 

Station 310 than Station 304 for both unadjusted and lengthadjusted models (Table 10). It is not possible with the current 

study design (that is, measuring concentrations in composite 

samples) to definitively account for the contribution of size to 

concentrations of Hg. However, our results indicate patterns 

of concentrations in northern pike were similar for Hg and 
Results and Discussion 27

Table 9. Unweighted geometric mean, minimum, and maximum concentrations (μg/g, wet-weight) of elemental 

contaminants in fish collected in the Yukon River Basin in 2002. Censored values were replaced by one-half the 

value for the LOD for the computation of station means, but only if at least one value exceeded detection limits. 

The maximum geometric station mean is shown in bold for each contaminant. Stations are listed upstream to 

downstream. 

Element Station As Cd Cr Cu Hg Ni Se Zn

Charley-Kandik, AK Mean 0.11 0.01 0.84 1.06 0.18 0.35 0.58 26.7 

(301) Min. 0.04 <0.02 0.26 0.53 0.15 <0.22 0.47 21.5 

(n = 4) Max. 0.17 0.12 1.66 1.49 0.28 0.71 0.66 46.1 

Fish Hook Bend, AK Mean 0.08 <0.02 0.32 0.43 0.22 <0.23 0.72 43.3 

(302) Min. 0.07 <0.02 0.30 0.42 0.21 <0.23 0.72 41.5 

(n = 2) Max. 0.10 <0.02 0.32 0.49 0.26 <0.23 0.73 49.1 

Fort Yukon, AK (303) Mean 0.06 <0.02 0.19 0.50 0.16 <0.24 0.56 46.6 

(n = 2) Min. 0.05 <0.02 <0.24 0.48 0.15 <0.23 0.53 44.6 

Max. 0.08 <0.02 0.30 0.52 0.16 <0.24 0.58 48.4 

The Bridge, AK (304) Mean 0.44 0.01 0.36 0.63 0.41 <0.27 0.46 42.2 

(n = 3) Min. 0.05 <0.03 0.28 0.52 0.19 <0.26 0.41 19.6 

Max. 1.08 0.09 0.85 1.16 0.56 <0.27 0.60 51.9 

Fairbanks, AK (305) Mean 0.12 0.01 0.23 0.97 0.17 <0.24 0.61 18.4 

(n = 5) Min. 0.05 <0.02 <0.22 0.57 0.09 <0.22 0.52 12.4 

Max. 0.46 0.04 0.40 1.31 0.30 <0.24 0.85 52.3 

Tolovana, AK (306) Mean 0.07 0.02 0.73 0.53 0.36 <0.25 0.48 39.2 

(n = 4) Min. 0.03 <0.03 0.40 0.51 0.08 <0.24 0.46 16.5 

Max. 0.08 0.06 0.94 0.72 0.65 <0.25 0.59 46.2 

Tanana, AK (307) Mean 0.17 <0.03 0.37 0.59 0.39 <0.25 0.43 42.9 

(n = 2) Min. 0.11 <0.02 0.37 0.55 0.37 <0.24 0.43 41.5 

Max. 0.30 <0.03 0.38 0.61 0.42 <0.25 0.45 45.3 

Galena, AK (308) Mean 0.06 0.02 0.63 0.59 0.24 <0.26 0.42 33.2 

(n = 4) Min. 0.05 <0.03 0.35 0.44 0.10 <0.25 0.34 15.6 

Max. 0.07 0.10 1.26 0.97 0.34 <0.26 0.55 46.8 

Innoko, AK (309) Mean 0.08 <0.03 0.22 0.42 0.25 <0.26 0.24 49.8 

(n = 2) Min. 0.06 <0.02 <0.26 0.41 0.25 <0.24 0.23 45.5 

Max. 0.10 <0.03 0.34 0.44 0.25 <0.26 0.25 56.4 

Kotlik, AK (310) Mean 0.28 <0.02 0.17 0.51 0.12 <0.24 0.28 39.3 

(n = 3) Min. 0.21 <0.02 <0.24 0.47 0.11 <0.21 0.23 10.5 

Max. 1.95 <0.02 0.24 0.62 0.13 <0.24 0.54 45.2 

HgL, and stations were identified where Hg could pose a risk. 

Future studies may be warranted to address specific concerns 

for Hg. 

Mercury data from the YRB were compared with concentrations from previous studies within the basin. Historical 

NCBP concentrations of Hg in longnose sucker (<0.01-0.14 

μg/g ww) (Schmitt and others, 1999b) were slightly less than 

concentrations measured in 2002 (0.08-0.19 μg/g ww). NCBP 

data were limited to two years (1981 and 1986) for northern 

pike (0.12-0.14 μg/g ww) and one year (1979) for burbot (0.21 

μg/g ww). Concentrations of Hg were also measured in whole 

body samples of northern pike from the MRB (Schmitt and 

others, 2002a) and RGB (Schmitt and others, 2004). Concentrations were 0.15 μg/g ww in a northern pike from the 
28 Environmental Contaminants and their Effects on Fish

Table 10. Spatial trends of chemical contaminants in fish collected in the Yukon River 

Basin in 2002. Least-squares mean concentrations (all in μg/g ww unless otherwise 

noted) of mercury (Hg), length-adjusted Hg (HgL; μg/g/m ww), weight-adjusted Hg 

(HgW; μg/g/kg ww), and selenium (Se). Values within each group of taxon-station 

means followed by the same letter are not significantly different (P<0.01, Fisher’s 

protected LSD). Also shown are ANOVA F-values and degrees-of-freedom (df), and 

significance levels (** P�0.01; *0.01<P�0.05; ns P>0.05). Stations are listed upstream to 

downstream within each taxon grouping. 

HgL 

Northern Pike 

Charley-Kandik, AK (301) 0.040 abcd 0.014 0.109 abc 0.259 de 

Fish Hook Bend, AK (302) 0.035 abc 0.023 0.116 abc 0.472 e 

Fort Yukon, AK (303) 0.014 ab 0.030 0.065 ab 0.259 de 

The Bridge, AK (304) 0.210 d 0.051 0.560 c 0.162 cd 

Fairbanks, AK (305) 0.022 abc 0.009 0.063 abc 0.265 cde 

Tolovana, AK (306) 0.135 cd 0.040 0.390 bc 0.171 cd 

Tanana, AK (307) 0.117 cd 0.027 0.344 bc 0.148 cd 

Galena, AK (308) 0.081 cd 0.037 0.252 bc 0.102 bc 

Innoko, AK (309) 0.041 bcd 0.017 0.137 abc 0.037 a 

Kotlik, AK (310) 0.008 a 0.004 0.024 a 0.047 ab 

Longnose sucker 

Charley-Kandik, AK (301) 0.017 a 0.047 a 0.102 a 0.250 a 

The Bridge, AK (304) 0.022 a 0.028 a 0.128 a 0.308 a 

Fairbanks, AK (305) 0.008 a 0.032 a 0.064 a 0.266 a 

Tolovana, AK (306) 0.005 a 0.023 a 0.042 a 0.279 a 

Galena, AK (308) 0.005 a 0.008 a 0.034 a 0.198 a 

Burbot 

Fairbanks, AK (305) 0.044 a 0.014 a 0.124 a 0.542 a 

Kotlik, AK (310) 0.009 a 0.008 a 0.031 a 0.242 a 

F-value 7.80 ** 0.98 ns 3.93 ** 10.74 ** 

df (model,error) 16,14 14,16 16,14 16,14 

Upper Missouri River and range from <0.02 to 0.18 μg/g ww μg/g ww) and burbot (0.098 μg/g ww) muscle in the Yukonin northern pike from the upper Rio Grande. Few YRB stud- Kuskokwim delta region of Alaska. Concentrations of Hg in 

ies examining whole body concentrations of Hg were found, fish from this region of Alaska were similar to those measured 

although several USFWS studies on NWRs reported concen- in fish from rivers in the contiguous U.S. (Duffy and others, 

trations in northern pike muscle. Whole body concentrations 1998; Yeardley and others, 1998). The NCP determined northof Hg in northern pike ranged from 0.07 to 0.11 μg/g ww from ern pike muscle samples from the Yukon Territory within the 

the Kanuti NWR in 1985 (Mueller and others, 1995) and 0.33- YRB to have concentrations of Hg <0.5 μg/g ww from 1996 

0.91 μg/g ww in northern pike muscle samples from several to 2000 (NCP, 2003). Mueller and others (1995) determined 

NWRs in 1991 (Mueller and others, 1996). Mueller and Matz northern pike consistently had the greatest concentrations of 

(2002) reported northern pike muscle concentrations ranging Hg of all species, a pattern that was also found in 2002.

from 0.07 to 0.86 μg/g ww in the Innoko NWR in 1996-1997. Laboratory toxicity test concentrations were compared to 

Jewett and others (2003) measured northern pike muscle con- Hg data from the YRB. Many Hg toxicity studies in adult fish 

centrations of total Hg of 1.5 μg/g ww collected in 2000 from are associated with concentrations that are not environmentally 

a tributary of the lower Yukon River. Duffy and others (1999) relevant (Wiener and Spry, 1996). Fish are at greatest risk 

determined mean concentrations of Hg in northern pike (0.823 from Hg at environmental exposure levels during embryonic 

HgW 

Contaminant Station and Species 

Hg Se 
Results and Discussion 29

μg/g μg/g μg/g

1

0.75

0.5

0.25

0

1

0.75

0.5

0.25

0

1

0.75

0.5

0.25

0

Hg 

HgL 

HgW 

Northern pike 

Longnose sucker 

Burbot 

301 302 303 304 305 306 307 308 309 310

Station 

Figure 5. Concentrations (μg/g ww) of mercury (Hg) by station and 

species in whole body fish composite samples collected in the 

Yukon River Basin in 2002. Unadjusted (Hg), length-adjusted (HgL), 

and weight-adjusted (HgW) concentrations are shown. Censored 

values are plotted as one-half the LOD. Stations are ordered 

upstream to downstream. See text for computations and Table 1 

for station descriptions.

and larval stages partially due to maternal transfer (Wiener 

and Spry, 1996). Behavioral effects in laboratory studies have 

been documented in fish containing whole body concentrations of 0.7-5.4 μg/g ww (Kania and O’Hara, 1974; Wiener 

and Spry, 1996). Grayling (Thymallus thymallus) fry with 

concentrations of 0.27 μg/g ww had permanent impairment 

of their feeding efficiency and competitive ability (Fjeld and 

others, 1998). Jarvinen and Ankley (1999) reviewed various 

laboratory studies evaluating the effects of Hg on reproduction in freshwater fish, including studies that found reduced 

reproduction at whole body concentrations of 4.47 μg/g ww 

in fathead minnows (Snarski and Olson, 1982) and 9.4 μg/g 

ww in second-generation brook trout (Salvelinus fontinalis)

(McKim and others, 1976). Dietary concentrations of Hg at 

0.87 μg/g dw (about 0.17 μg/g ww assuming 80% moisture) 

increased whole body concentrations of Hg more than 10-fold, 

suppressed hormone levels, and inhibited gonadal development in female fathead minnows (Drevnick and Sandheinrich, 

2003). Whole body concentrations associated with behavioral 

and reproductive effects were approximately 5 μg/g ww for 

brook trout and 10 μg/g ww for rainbow trout (Wiener and 

Spry, 1996; Wiener and others, 2002). However, caution 

should be used with these thresholds because many factors 

can contribute uncertainty to these critical tissue concentration 

estimates (Wiener and others, 2002).

Dietary concentrations of Hg in wildlife as low as 0.3 

μg/g ww have been associated with reproductive impairment 

in common loons (Gavia immer) (Barr, 1986), and reproduction in mallards (Anas platyrhynchos) was affected at concentrations as low as 0.1 μg/g ww (Heinz, 1979). Dietary 

concentrations of Hg from 0.25 to 1.0 μg/g ww may also be 

toxic to piscivorous mammals (studies reviewed by Wolfe and 

others, 1998). Neurotoxicity and mortality occurred in adult 

mink (Mustela vison) after chronic exposure to dietary concentrations of Hg >1 μg/g ww (Dansereau and others, 1999; 

Wobeser and others, 1976; Wren and others, 1987). Consequently, guidelines for the protection of piscivorous wildlife 

range from 0.5 to 1.0 μg/g ww (Eisler, 1987; Thompson, 1996) 

and values as low as 0.1 μg/g ww for mammals and 0.02 μg/g 

ww for birds have been derived from water quality criteria 

and bioaccumulation factors (Yeardley and others, 1998). 

Selenium affords a degree of protection against Hg toxicity in 

wildlife by demethylation to inorganic mercury when Se and 

Hg are in molar ratio of 1:1 (Dietz and others, 1990; Hamilton, 

2004; Heinz and Hoffman, 1998; Scheuhammer and others, 

1998; Wiener and others, 2002). However, studies have shown 

Se-enhanced Hg embryotoxicity in birds (Heinz and Hoffman, 

1998). Consequently, reproductive effects may be exacerbated 

even though significant amounts of Se may protect adult birds 

from the toxic effects of Hg. Concentrations of Hg in northern 

pike at Stations 304, 306, 307, and 308 and burbot from Station 305 exceeded 0.3 μg/g ww, and at least one sample from 

all stations exceeded 0.1 μg/g ww (Fig. 5). Therefore, our 

results indicate that Hg is a cause of concern in YRB.

Lead

Concentrations of Pb in fish from the YRB were <LOD 

(0.21-0.27 μg/g ww) in all composite samples (Table 8). 

Historical NCBP concentrations of Pb were also very low 

(<0.2 μg/g ww) in northern pike, longnose sucker, and burbot 
30 Environmental Contaminants and their Effects on Fish

(Schmitt and others, 1999b). Several other studies from the 

region reported similar low concentrations for Pb. Whole 

body concentration of Pb were <LOD (0.025 μg/g ww) in 

northern pike samples from the Kanuti NWR in 1985 (Mueller and others, 1995), and concentrations of Pb were <LOD in 

northern pike muscle samples from the Innoko and Koyukuk 

NWRs in recent years (Mueller and Matz, 2002; Snyder-Conn 

and others, 1992). Lead in sediment from Alaskan placer 

mining settling ponds within the YRB were less than concentrations that have been determined to affect fish and wildlife 

(Scannell, 1997). The threshold for the effects of Pb in fish is 

≥0.4 μg/g ww based on whole body concentrations (Holcombe 

and others, 1976 as reviewed in Jarvinen and Ankley, 1999); 

therefore, Pb is not a contaminant of concern in the YRB.

Cadmium

Concentrations of Cd in longnose sucker from the CRB 

were >LOD (0.02-0.03 μg/g ww) in nine samples (29%) from 

five stations, whereas concentrations in northern pike and 

burbot were universally <LOD (Table 8; Fig. 6). All longnose 

sucker composite samples were ≤0.12 μg/g ww with the maximum concentration (0.12 μg/g ww) measured in females from 

Station 301 (Fig. 6). The greatest geometric station mean was 

calculated for samples at Stations 306 and 308 (0.02 μg/g ww) 

(Table 9).

Concentrations of Cd from the YRB were compared to 

historical NCBP concentrations in northern pike, longnose 

sucker, and burbot collected near Fairbanks from 1971 to 1986 

(Schmitt and others, 1999b). Concentrations of Cd in northern 

pike, burbot, and longnose sucker from Station 305 were similar to historical concentrations. Other stations in the basin had 

concentrations slightly greater than the historical NCBP data. 

Concentrations of Cd were <LOD in northern pike muscle 

samples from the Koyukuk and Innoko NWRs in 1987 to 1988 

(Snyder-Conn and others, 1992). Mueller and others (1995) 

reported that longnose sucker from Kanuti NWR had greater 

concentrations of Cd than other species including northern 

pike, a pattern that was also apparent in longnose sucker and 

northern pike concentrations in 2002.

Concentrations of Cd in fish collected during 2002 in the 

YRB were compared to laboratory toxicity tests and wildlife criteria. Birds and mammals are comparatively resistant 

to Cd; dietary toxicity thresholds were >100 μg/g ww in 

the studies reviewed by Eisler (1985). Nevertheless, Eisler 

(1985) suggested that a Cd concentration of 2 μg/g ww in fish 

is evidence of contamination, that 5 μg/g ww is potentially 

life-threatening to the fish, and that 13-15 μg/g ww is a threat 

to higher trophic levels. A review by Jarvinen and Ankley 

(1999) included several laboratory studies in which whole 

body concentrations of Cd in freshwater fish ranging from 

0.12 to 15.6 μg/g ww resulted in reduced survival, growth, 

or both and concentrations of 2-8 μg/g ww caused decreased 

spawning and number of embryos produced in freshwater fish. 

μg/g 

0.2

0.15

0.1

0.05

0

Cd Northern pike 

Longnose sucker 

Burbot 

301 302 303 304 305 306 307 308 309 310

Station 

Figure 6. Concentrations (μg/g ww) of cadmium (Cd) by station 

and species in whole body fish composite samples collected in 

the Yukon River Basin in 2002. Censored values are plotted as onehalf the LOD. Stations are ordered upstream to downstream. See 

Table 1 for station descriptions.

Concentrations of Cd in the YRB were less than these benchmarks.

Zinc

Concentrations of Zn in fish from the YRB ranged 

from 10.5 to 56.4 μg/g ww, with the maximum concentration 

measured in female northern pike from Station 309 (Table 

8; Fig. 7). Burbot samples had the lowest concentrations of 

Zn (<15.5 μg/g ww), followed by concentrations in longnose 

sucker (15.6-30.8 μg/g ww), and northern pike had the greatest 

concentrations (35.4-56.4 μg/g ww). Geometric station means 

were similar, although fish samples from Stations 301 and 305 

had lower concentrations than the other stations (Table 9).

Concentrations of Zn in 2002 were similar to historical NCBP concentrations collected near Fairbanks (Schmitt 

and others, 1999b). Northern pike had concentrations of Zn 

ranging from 28.6 to 32.2 μg/g ww in 1981 and 1986, which 

is slightly lower than the concentrations measured in 2002 

samples. Concentrations of Zn in burbot (8.5 μg/g ww) were 

only available for 1979. Concentrations in longnose sucker 

from 1979 to 1984 ranged from 13.3 to 16.5 μg/g ww. YRB 

concentrations of Zn in northern pike were similar to concentrations from the RGB (28-56 μg/g ww) and MRB (31.8 μg/g 

ww) although sample sizes were limited (Schmitt and others, 

2002a; 2004). Other studies measuring whole body concentrations of Zn in northern pike, longnose sucker, and burbot from 

the YRB were not found. The USFWS has sampled multiple 

NWRs in the YRB, but these studies measured concentrations 

<10 μg/g ww in northern pike muscle only. Sun and Jeng 
31

80

60

40

20

0

2

1.5

1

0.5

0

2

1.5

1

0.5

0

1

0.75

0.5

0.25

0

301 302 303 304 305 306 307 308 309 310

Station 

Figure 7. Concentrations (μg/g ww) of zinc (Zn), copper (Cu), 

chromium (Cr), and nickel (Ni) by station and species in whole 

body fish composite samples collected in the Yukon River Basin in 

2002. Censored values are plotted as one-half the LOD. Stations 

are ordered upstream to downstream. See Table 1 for station 

descriptions.

μg/g μg/g μg/g μg/g 

Zn 

Cu 

Cr 

Ni 

Northern pike 

Longnose sucker 

Burbot 

Results and Discussion

(1998) determined that fish species vary in Zn partitioning in 

tissues. Muscle tissues had lower concentrations of Zn compared to most other tissues examined including digestive tract 

tissue, liver, kidney, gonad, gill, and skeletal tissues (Sun and 

Jeng, 1998). Therefore, it may be inappropriate to compare 

2002 concentrations with USFWS northern pike data. Concentrations of Zn in sediment from Alaskan placer mining settling ponds in the YRB were less than concentrations that have 

been determined to affect fish and wildlife (Scannell, 1997).

Laboratory toxicity tests for Zn were limited as well. The 

growth and survival of American flagfish (Jordanella floridae), a cyprinid, exposed over a life-cycle (larvae-to-adult) 

were affected at concentrations of 40-64 μg/g ww (Spehar, 

1976 as cited by Jarvinen and Ankley, 1999). Eisler (1993) 

concluded that it is unlikely that either fish or higher trophic 

level organisms are adversely affected by Zn. Concentrations 

of Zn do not appear to be a contaminant of concern in northern 

pike, longnose sucker, and burbot collected from the YRB.

Copper

Copper was detected in all samples at concentrations 

ranging from 0.41 to 1.49 μg/g ww, with the maximum measured in female longnose sucker from Station 301 (Table 8). 

Longnose sucker samples consistently had greater concentrations of Cu (>0.62 μg/g ww) compared to northern pike (most 

<0.60 μg/g ww) (Fig. 7). Concentrations of Cu were greatest 

in longnose sucker from Stations 301, 304, and 305, and fish 

samples from Stations 301 and 305 had the greatest geometric 

stations means (1.06 and 0.97 μg/g ww, respectively) (Table 

9).

YRB concentrations of Cu were compared to NCBP data 

collected from 1979 to 1986 (Schmitt and others, 1999b). 

Historical concentrations were less than 2002 concentrations 

in burbot and northern pike, whereas historical concentrations 

of Cu (0.6-1.2 μg/g ww) in longnose sucker were similar to 

2002 concentrations at Station 305 (1.0-1.3 μg/g ww). Concentrations of Cu in northern pike from the RGB in 1997 were 

slightly greater (0.74-1.0 μg/g ww) (Schmitt and others, 2004) 

than YRB northern pike concentrations. Additional studies examining whole body concentrations of Cu in northern 

pike, longnose sucker, and burbot were not found. However, 

the USFWS collected northern pike muscle samples from the 

Koyukuk and Innoko NWRs in the YRB (Mueller and Matz, 

2002; Snyder-Conn and others, 1992). Concentrations in 

these studies were less than 2002 concentrations (<0.4 μg/g 

ww) although this may be attributed to the partitioning of Cu 

into tissues other than muscle, primarily the liver (Aaseth and 

Norseth, 1986) and kidney (West and Deschu, 1984). Mueller and others (1995) reported that longnose sucker from the 

Kanuti NWR had greater concentrations of Cu than other species including northern pike, a pattern that was also apparent 

in our data. Scannell (1997) concluded that concentrations 

of Cu in sediment from Alaskan placer mining settling ponds 
32 Environmental Contaminants and their Effects on Fish

were less than concentrations that negatively affect fish and 

wildlife.

The ecological relevance of the concentrations of Cu in 

fish from the YRB is unknown. Of the studies reviewed by 

Jarvinen and Ankley (1999), only the work of Stouthart and 

others (1996) was relevant; these authors determined that 

concentrations of 11.1-11.7 μg/g ww were associated with 

reduced survival of carp larvae, and concentrations of 42 μg/g 

ww reduced egg survival. However, no tissue-based criteria 

for Cu are available for the protection of avian and mammalian 

wildlife (Eisler, 1997).

Chromium and Nickel

Concentrations of Cr were >LOD (0.22-0.26 μg/g ww) in 

29 of 31 composite samples (84%) from all stations (Table 8). 

Concentrations ranged from 0.23 to 1.64 μg/g ww, with the 

maximum concentration measured in female longnose sucker 

from Station 301 (Table 8; Fig. 7). Geometric station means in 

fish were <0.84 μg/g ww (Table 9). Concentrations of Cr were 

not determined by the NCBP (Schmitt and others, 1999b). 

Concentrations of Cr in northern pike from the RGB in 1997 

(0.28-0.88 μg/g ww) (Schmitt and others, 2004) were less than 

those in the YRB. Additional studies examining whole body 

concentrations of Cu in northern pike, longnose sucker, and 

burbot were not found. However, the USFWS collected northern pike muscle samples from the Koyukuk and Innoko NWRs 

in the YRB (Mueller and Matz, 2002; Snyder-Conn and others, 1992). These studies reported few concentrations of Cr 

>LOD in northern pike muscle, possibly as a result of Cr accumulating in other tissues (Langard and Norseth, 1986). Eisler 

(1986) suggested that concentrations of Cr >4 μg/g ww may 

be considered contaminated; however, the significance of such 

a value is unclear. A review of the literature (Jarvinen and 

Ankley, 1999) did not find studies linking whole body residues 

of Cr to survival or growth effects in freshwater fishes.

Concentrations of Ni were >LOD (0.21-0.27 μg/g ww) 

in 2 of 31 composite samples (6%) (Table 8). Concentrations 

ranged from 1.0 to 2.9 μg/g ww, with the maximum concentration measured in female longnose sucker from Station 

301 (Table 8; Fig. 7). Geometric station means were <LOD 

for all samples, with the exception of fish from Station 301 

(0.35 μg/g ww) (Table 9). Whole body concentrations of Ni 

ranged from 0.19 to 0.73 μg/g ww in northern pike from the 

RGB (Schmitt and others, 2004). Concentrations of Ni in 

most northern pike muscle samples from various NWRs in the 

YRB were also <LOD (Mueller and others, 1995; Mueller and 

Matz, 2002; Snyder-Conn, 1992). Scannell (1997) determined that concentrations of Ni in sediment from Alaskan 

placer mining settling ponds were less than concentrations that 

negatively affect fish and wildlife. Like Cu, studies are lacking for linkages of whole body concentrations to effects for Ni 

(Jarvinen and Ankley, 1999), and tissue-based criteria for the 

protection of fishes and piscivorous wildlife are not available.

Data for additional elements and other data from this 

study are available at <http://www.cerc.usgs.gov/data/search.

htm>.

Organochlorine Chemicals

DDT and Its Primary Metabolites

DDT, a persistent organochlorine insecticide, and its 

metabolites remain present in the environment as a consequence of atmospheric transport and from historical use in 

the U.S. until 1972. Elevated concentrations of residues 

derived from DDT are most common in cotton-growing areas 

of the U.S. and near former sites of production and formulation, although atmospheric transport from sites where DDT 

is still used can also deposit these chemicals (Schmitt and 

others, 2002a). We found the parent compound, p,p’-DDT, 

at concentrations >LOD (0.0007-0.0008 μg/g ww) in only 2 

of 31 samples (6%). Both detected samples were from Station 305 (Table 11), and p,p’-DDT accounted for 31% of the 

total detected DDT (p,p’-homologs) in fish sampled in 2002 

(Fig. 8). The greatest concentrations (individual samples and 

geometric station means) were in female northern pike (0.0091 

μg/g ww) and male longnose sucker (0.0047 μg/g ww) from 

Station 305 (Tables 11 and 12).

The major metabolite of p,p’-DDT, p,p’-DDE, was 

detected in 25 of 31 fish composites (Table 11) and accounted 

for 44% of the total detected DDT (Fig. 8). Fish samples 

from Station 304 had concentrations <LOD (0.0002 μg/g ww), 

whereas the female longnose sucker sample from Station 305 

had the greatest concentration of p,p’-DDE (0.005 μg/g ww) 

(Fig. 9).

YRB concentrations of p,p’-DDE were compared to 

NCBP data collected near Fairbanks from 1969 to 1986 

(Schmitt and others, 1999b). Historical data on p,p’-DDE 

were limited for northern pike (1981, 1986) and burbot (1979) 

but were greater than those measured in 2002. Longnose 

sucker had the most extensive historical data (1969-1984) and 

showed a decreasing p,p’-DDE trend during the NCBP collection years and continued with 2002 concentrations.

Concentrations of p,p’-DDD are a result of p,p’-DDT 

breakdown and use as an insecticide. This compound 

accounted for 26% of the total detected DDT (Fig. 8) and was 

detected (≥0.0002 μg/g ww) in 18 of 31 composite samples 

(81%) from eight stations (Table 11). Female longnose sucker 

from Station 305 had the greatest concentration of p,p’-DDD 

(0.007 μg/g ww) with all other composite samples having 

concentrations <0.004 μg/g ww.

Geometric means for total DDT were highest in fish at 

Station 305 (0.011 μg/g ww), and all other station means were 

≤0.004 μg/g ww (Table 12). Low historical concentrations 

of total DDT have been recorded at Station 305 (Schmitt and 

others, 1999b). Snyder-Conn (1992) reported similar find-
Results and Discussion 33

Table 11. Percent of samples and stations with concentrations exceeding the limit of detection (LOD) for organochlorine chemical 

residues in composite samples of whole fish in the Yukon River Basin in 2002. The maximum concentrations and associated sample 

information (station, species, and gender) from this study are also given. a Sum of cis- and trans-chlordanes and nonachlors; 

oxychlordane; and heptachlor epoxide, with censored values represented as 50% LOD. b 1,1a,2,2,3,3a,4,5,5,5a,5b,6-Dodecachlorooctahydro-1,3,4-metheno-1H-cyclobuta(cd)pentalene. 

Analyte(s) 

Samples Stations 

(% of 31) (% of 10) μg/g Gender Species 

Maximum 2002 Concentration 

Station 

p,p’-DDT 6 10 0.009 Fairbanks (305) F Northern pike 

p,p’-DDD (TDE) 58 80 0.007 Fairbanks (305) F Longnose sucker 

p,p’-DDE 81 100 0.005 Fairbanks (305) F Longnose sucker 

Total p,p’-homologs 81 100 0.014 Fairbanks (305) F Northern pike 

o,p’-DDT 68 70 0.003 Fairbanks (305) F Longnose sucker 

o,p’-DDD (TDE) 10 30 0.003 Galena (308) F Longnose sucker 

o,p’-DDE 42 70 0.002 Charley-Kandik (301) M Longnose sucker 

Dieldrin 35 70 0.001 The Bridge (304) F Longnose sucker 

Endrin 35 80 0.001 Charley-Kandik (301) F Longnose sucker 

cis-Chlordane 29 50 0.001 Tolovana (306) F Northern pike 

trans-Chlordane 58 80 0.002 Tanana (307) M Northern pike 

cis-Nonachlor 90 100 0.002 Fairbanks (305) M Longnose sucker 

trans-Nonachlor 45 70 0.002 Tolovana (306) F Northern pike 

Oxychlordane 58 80 0.003 Charley-Kandik (301) F Longnose sucker 

Heptachlor epoxide 16 40 0.001 Fairbanks (305) F Burbot 

Total chlordane-related residues

 a 94 100 0.007 Tolovana (306) F Northern pike 

Toxaphene 34 80 0.034 Fish Hook Bend (302) F Northern pike 

Mirex b 32 60 0.0003 Fish Hook Bend (302) M Northern pike 

Total PCBs 90 90 0.087 Fairbanks (305) F Longnose sucker 

ings in the Tanana basin with northern pike and burbot having 

undetectable or only trace (0.02 μg/g ww) concentrations 

of p,p’-DDE. Concentrations of p,p’-DDT in burbot livers 

collected near Fairbanks were greater than NWR concentrations in the YRB (Mueller and Matz, 2000), with the city of 

Fairbanks, Fort Wainwright Army Base, and Eielson Air Force 

Base identified as the probable local contamination sources.

Concentrations of total DDT in our study were compared 

to laboratory toxicity tests and wildlife criteria. Concentrations of total DDT in fish >0.15 μg/g ww are potentially 

harmful to the brown pelican (Pelicanus occidentalis), a 

sensitive avian species (Anderson and others, 1975), and 

wildlife criteria as low as 0.20 μg/g ww have been suggested 

by Newell and others (1987). Concentrations of 1-3 μg/g ww 

are potentially hazardous to most piscivorous birds (see review 

by Blus, 1996). A review by Jarvinen and Ankley (1999) 

associated toxic effects of total DDT to fish with whole body 

concentrations as low as 0.5 μg/g ww. Reduced survival has 

been reported with whole body concentrations of total DDT 

in fry or fingerlings of cutthroat trout (O. clarki; 0.57 μg/g 

ww) (Cuerrier and others, 1967), rainbow trout (1.14-1.42 

μg/g ww) (Cuerrier and others, 1967; Hopkins and others, 

1969), brook trout (0.46-5.03 μg/g ww) (Cuerrier and others, 1967; Macek, 1968), lake trout (S. namaycush; 2.93 μg/g 

ww) (Burdick and others, 1964), coho salmon (1.09-2.76 μg/g 

ww) (Johnson and Pecor, 1969), and chinook salmon (11.6-

21.7 μg/g ww) (Buhler and others, 1969). Reduced survival 

has been reported with whole body concentrations of total 

DDT in juvenile and adult green sunfish (Lepomis cyanellus) 

and pumpkinseed (L. gibbosus; 24 μg/g ww) (Hamelink and 

others, 1971), fathead minnows (57-209 μg/g ww) (Jarvinen 

and others, 1976; Jarvinen and others, 1977), and goldfish 

(Carassius auratus; 200-400 μg/g ww) (Rhead and Perkins, 

1984). Concentrations of total DDT in 2002 were less than 

these benchmarks and were not identified as hazardous to fish 

or wildlife in the YRB.

Technical DDT contains o,p’-DDT as an impurity, and 

residues of this compound and its metabolites also remain 

widespread (Schmitt and others, 1985; 1999b; 2002a). Comparatively low concentrations of o,p’-DDT (<0.0001–0.003 

μg/g ww) were detected in composite samples from the YRB. 

The o,p’-homologs have historically been considered relatively 

benign, although o,p’-DDD has been shown to be weakly 

estrogenic (Ackerman and others, 2002; Guillette and others, 
34 Environmental Contaminants and their Effects on Fish

μg/g 

wet-weight 

0.01

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

0

DDT 

DDE 

DDD 

301 302 303 304 305 306 307 308 309 310

Station 

Figure 8. Weighted geometric mean concentrations (μg/g ww) of p,p’-DDT, DDE, and DDD by station in whole body fish composite 

samples collected in the Yukon River Basin in 2002. Censored values are represented by one-half the LOD in the computation of means 

and totals but are not shown in the figure. Stations are ordered upstream to downstream. See Table 1 for station descriptions.

1996; Toppari and others, 1996), as are many other pesticides 

and their metabolites (Tyler and others, 1998). The total risk 

to fish and wildlife represented by concentrations of o,p’-DDT 

is unknown, but these chemicals are not considered to be of 

concern at the concentrations measured in 2002.

Cyclodiene Pesticides

Chlordane and Heptachlor

Chlordane is a mixture of cyclopentadiene-derived compounds that was widely used as a soil insecticide. Concentrations of these compounds are typically greatest in fish from 

corn-growing regions, urban areas in the “termite belt”, and 

near production and formulation facilities (Schmitt, 2002b; 

Schmitt and others, 1999b) and were not expected to measured 

at high concentrations in the YRB. Six chlordane-related 

components and metabolites were measured in the 2002 samples including cis-chlordane, trans-chlordane, cis-nonachlor, 

trans-nonachlor, oxychlordane, and heptachlor epoxide (Table 

11). Concentrations of all six chlordane-related compounds 

were low (<0.003 μg/g ww) in all composite samples (Table 

11). NCBP concentrations from fish samples collected from 

1977 to 1986 for all of these compounds were <LOD (<0.005-

0.01 μg/g ww; Schmitt and others, 1999b). Snyder-Conn 

(1992) also reported chlordane compounds <LOD (0.01 μg/g 

ww) in northern pike and burbot from a lake within the YRB.

Concentrations of total chlordanes (sum of six compounds) in 2002 ranged from <0.001 to 0.007 μg/g ww, with 

the maximum concentration measured in female northern 

pike from Station 306 (Fig. 9). All geometric station means 

for total chlordane were ≤0.005 μg/g ww (Table 12; Fig. 10). 

All fish samples from the YRB had concentrations of total 

chlordane <0.1 μg/g ww, the level of concern for the health of 

predatory fish and fish-eating birds (Eisler, 1990).

Dieldrin

Most environmental dieldrin is present due to the break-
Results and Discussion 35

Table 12. Unweighted geometric mean, minimum, and maximum concentrations (μg/g ww) of 

organochlorine chemical contaminants in fish collected from stations in the Yukon River Basin 

in 2002. Censored values were replaced by one-half of the value for the LOD for the 

computation of station means, but only if at least one value exceeded LOD. Total DDT are the 

total of p,p’-DDT homologs. Total PCBs is the sum of all congeners. Total chlordane is the 

sum of cis-chlordane, trans-chlordane, cis-nonachlor, trans-nonachlor, heptachlor epoxide 

and oxychlordane. The maximum geometric station mean is shown in bold for each 

contaminant. Stations are listed upstream to downstream. 

Station 

Charley-Kandik, AK Mean 0.002 0.0001 0.036 0.007 0.003 

(301) Min. 0.001 <0.0002 0.025 <0.011 0.001 

(n = 4) Max. 0.004 0.0002 0.040 0.033 0.004 

Fish Hook Bend, AK Mean 0.004 <0.0002 0.042 0.032 0.003 

(302) Min. 0.004 <0.0002 0.040 0.029 0.003 

(n = 2) Max. 0.005 <0.0002 0.048 0.034 0.004 

Fort Yukon, AK (303) Mean 0.001 <0.0002 <0.02 <0.011 0.001 

(n = 2) Min. 0.001 <0.0002 <0.02 <0.011 0.001 

Max. 0.002 <0.0002 <0.02 <0.011 0.001 

The Bridge, AK (304) Mean 0.001 0.0003 0.031 0.010 0.005

(n = 3) Min. 0.001 <0.0002 0.025 <0.011 0.003 

Max. 0.002 0.0006 0.033 0.013 0.006 

Fairbanks, AK (305) Mean 0.011 0.0001 0.062 0.007 0.002 

(n = 5) Min. 0.007 <0.0002 0.039 <0.011 0.001 

Max. 0.014 0.0003 0.087 0.019 0.004 

Tolovana, AK (306) Mean 0.004 0.0003 0.039 0.017 0.004 

(n = 4) Min. 0.003 <0.0002 0.026 <0.011 0.002 

Max. 0.005 0.0004 0.063 0.030 0.007 

Tanana, AK (307) Mean 0.003 0.0004 0.030 0.009 0.003 

(n = 2) Min. 0.002 0.0004 0.029 <0.011 0.002 

Max. 0.004 0.0005 0.031 0.014 0.005 

Galena, AK (308) Mean 0.002 0.0002 0.022 0.008 0.003 

(n = 4) Min. 0.001 <0.0002 0.019 <0.011 0.003 

Max. 0.002 0.0003 0.029 0.018 0.005 

Innoko, AK (309) Mean 0.001 <0.0002 0.024 0.009 0.001 

(n = 2) Min. 0.001 <0.0002 0.023 <0.011 0.001 

Max. 0.002 <0.0002 0.025 0.016 0.003 

Kotlik, AK (310) Mean 0.002 0.0001 0.015 <0.011 0.003 

(n = 3) Min. 0.001 <0.0002 <0.02 <0.011 0.002 

Max. 0.002 0.0003 0.022 <0.011 0.004 

Total 

DDT Dieldrin 

Total 

PCBs 

Toxaphene 

Total 

Chlordane 
36 Environmental Contaminants and their Effects on Fish

0.005

0.004

0.003

0.002

0.001

0

0.04

0.03

0.02

0.01

0

0.008

0.006

0.004

0.002

0

0.0008

0.0006

0.0004

0.0002

0

301 302 303 304 305 306 307 308 309 310

Toxaphene 

p,p'-DDE 

Total Chlordanes 

Dieldrin 

Northern pike 

Longnose sucker 

Burbot 

Station 

Figure 9. Concentrations (μg/g ww) of p,p’-DDE, toxaphene, total 

chlordanes, and dieldrin by station and species in whole body fish 

composite samples collected in the Yukon River Basin in 2002. 

Total chlordanes are the sum of cis- and trans-chlordanes and 

nonachlors, heptachlor epoxide, and oxychlordane. Censored 

values are plotted as one-half the LOD. Stations are ordered 

upstream to downstream. See Table 1 for station descriptions.

down of aldrin, which has not been used in the U.S. since 

1974. Concentrations ≥LOD (0.0002 μg/g ww) were found in 

35% of the samples from seven sites (Table 11). Concentrations were greatest (0.001 μg/g ww) in female northern pike 

from Station 304 (Fig. 9). All geometric station means were 

μg/g μg/g μg/g μg/g 

<0.0004 μg/g ww (Table 12). Historical NCBP concentrations of dieldrin were ≤LOD (<0.01 μg/g ww) in northern 

pike, longnose sucker, and burbot from Station 305 (Schmitt 

and others, 1999b). Dieldrin was <LOD (0.01 μg/g ww) in 

northern pike and burbot samples collected in 1989 from Lake 

Munchumia located within the YRB (Snyder-Conn, 1992).

Several laboratory studies examined the effects of dieldrin on fish. Whole body concentrations of 0.36-2.13 μg/g 

ww were determined to have no effect on survival or growth 

of juvenile rainbow trout (Macek and others, 1970; Shubat and 

Curtis, 1986 as cited in Jarvinen and Ankley, 1999). Juvenile rainbow trout experience reduced survival at whole body 

concentrations of 5.65 μg/g ww (Shubat and Curtis, 1986). 

The YRB concentrations of dieldrin are less than benchmarks 

set to protect fish and piscivores (Jarvinen and Ankley, 1999; 

Peakall, 1996).

Endrin

Endrin is one of the most toxic organochlorine pesticides 

to fish but was used on comparatively few crops historically 

(Johnson and Finley, 1980). YRB concentrations of endrin 

were <0.001 μg/g ww in all samples (Table 11). Historical 

NCBP concentrations of endrin were <LOD (0.005-0.01 μg/g 

ww) in fish samples from Station 305 (Schmitt and others, 

1999b), and endrin was not detected (<0.01 μg/g ww) in whole 

body northern pike or burbot samples in 1989 from Lake Munchumia located within the YRB (Snyder-Conn, 1992). Endrin 

is not considered a chemical of concern in the YRB.

Other Organochlorine Compounds

Mirex

Mirex was used as an insecticide to combat red imported 

fire ants (Solenopsis wagneri) in the southern U.S. Elsewhere, 

mirex was used as a flame retardant and as a polymerizing 

agent (Kaiser, 1987). Consistent with historical NCBP data 

from 1981 to 1986 (Schmitt and others, 1999b), concentrations of mirex were low (<0.0003 μg/g ww) in the 2002 YRB 

samples (Table 11). Snyder-Conn (1992) reported similar 

findings for mirex in northern pike and burbot from the YRB.

Toxaphene

Toxaphene was detected (0.012-0.034 μg/g ww) in multiple northern pike and longnose sucker samples in 2002 (Fig. 

9; Table 11), although all geometric station means were <0.05 

μg/g ww (Table 12). Toxaphene was the most heavily used 

insecticide in the U.S. following the ban on DDT (Schmitt 

and Winger, 1980). Use of toxaphene in the U.S. peaked in 

the late 1970s, and the pesticide was subsequently banned. 

Toxaphene has been atmospherically transported to remote 
Results and Discussion 37

μg/g 

wet-weight 

0.005 

0.004 

0.003 

0.002 

0.001 

0 

Heptachlor epoxide 

Oxychlodane 

cis-Chlordane 

trans-Chlordane 

cis-Nonachlor 

trans-Nonachlor 

301 302 303 304 305 306 307 308 309 310 

Station 

Figure 10. Weighted geometric mean concentrations (μg/g ww) of chlordane-related compounds (cis- and trans-chlordanes and 

nonachlors, heptachlor epoxide, and oxychlordane) by station in whole body fish composite samples collected in the Yukon River Basin 

in 2002. Censored values are represented by one-half the LOD in the computation of means and totals but are not shown in the figure. 

Stations are ordered upstream to downstream. See Table 1 for station descriptions.

locations, and residues have been detected in fish from the 

Arctic and the Great Lakes (Muir and others, 1999; Schmitt 

and others, 1999b). The NCBP program never detected 

concentrations (>0.1 μg/g ww) in fish samples near Fairbanks 

(Schmitt and others, 1999b). Snyder-Conn (1992) reported 

that northern pike and burbot from a lake within the YRB had 

concentrations of toxaphene <LOD (0.05 μg/g ww). Temporal 

trend analysis is difficult for toxaphene because there are a 

wide range of LODs from the various studies cited.

Toxaphene has been classified as the major organochlorine contaminant in the Canadian arctic by the NCP (NCP, 

2003). Concentrations of toxaphene were 125 times greater 

in burbot livers collected from Lake Laberge, Yukon Territory, 

within the YRB than in burbot from other arctic lakes (Braune 

and others, 1999). Concentrations of toxaphene in liver tend 

to be greater than in other tissues because of the high lipid 

content (Braune and others, 1999). High isolated concentrations of toxaphene in fish may exist within the YRB.

Concentrations of toxaphene from the YRB were 

compared to laboratory toxicity tests and wildlife thresholds. 

Acute and chronic effects of toxaphene on freshwater fish have 

been noted at whole body concentrations ≥0.4 μg/g ww (Eisler 

and Jacknow, 1985; Jarvinen and Ankley, 1999). Jarvinen 

and Ankley (1999) reviewed multiple laboratory studies on 

the acute and chronic effects of toxaphene, among these were 

several by Mayer and others (1975; 1978). These authors 

reported that adult brook trout containing whole body concentrations of 0.4 μg/g ww produced eggs with reduced viability, 

and lake trout and white sucker containing 0.035-0.203 μg/g 

ww also produced eggs with reduced viability (Mayer and 

others, 1975). Survival and growth of freshwater fish (several 

species) at various life stages were reduced at concentrations 

>0.90 μg/g ww (Mayer and others, 1975; 1978).

Hexachlorocyclohexanes (HCH)

Four relatively short-lived HCH isomers (α-, β-, δ-, γHCH) were measured in the 2002 YRB samples. A mixture of 

HCH isomers was historically used on cotton and other crops 
38 Environmental Contaminants and their Effects on Fish

in the U.S., but only γ-HCH (lindane) is still used in North 

America for some agricultural and domestic applications. 

All fish samples from the YRB had concentrations <0.01 

μg/g ww for these isomers. Concentrations of α- and γ-HCH 

were <LOD (0.01 μg/g ww) in fish collected from the NCBP 

site near Fairbanks from 1977 to 1986 (Schmitt and others, 

1999b). These results are consistent with previous data from 

the YRB (Snyder-Conn, 1992).

Hexachlorobenzene (HCB)

HCB was produced for use as a fungicide and was a 

by-product of the production of other chlorinated hydrocarbons. HCB has been considered less toxic to fish than many 

other persistent organochlorines, although it may contain toxic 

impurities (Schmitt and others, 1999b). Concentrations of 

HCB were <LOD (0.003 μg/g ww) in all samples from the 

YRB in 2002 and in historical NCBP concentrations (Schmitt 

and others, 1999b). These finding are similar to those of 

Snyder-Conn (1992) who reported concentrations of HCB in 

northern pike and burbot from a lake in the YRB to be <LOD 

(0.01 μg/g ww).

Total PCBs, H4IIE-Derived Dioxin Equivalents,

and Ethoxyresorufin O-Deethylase (EROD)

Activity

Total PCBs

Total PCBs exceeded the LOD (0.02 μg/g ww) in 28 of 

31 fish samples (90%) from nine stations (Table 11). Concentrations ranged from 0.02 to 0.09 μg/g ww, with the maximum 

concentration measured in a female longnose sucker sample 

from Station 305 (Table 11; Fig. 11). Four of the five greatest 

concentrations of total PCBs (≥0.05 μg/g ww) were measured 

in fish from Station 305 (Fig. 11). Geometric station means 

were <0.062 μg/g ww in all samples (Table 12).

Data from the YRB in 2002 were compared to other 

studies measuring concentrations of PCBs in fish. Concentrations of PCBs were lower in 2002 samples compared to historical NCBP concentrations (1969-1986) that measured Aroclor 

mixtures (1248, 1254, 1260) from Fairbanks (Schmitt and 

others, 1999b). Few YRB studies measuring PCBs in whole 

body samples exist. Whole body concentrations of PCBs in 

northern pike were 0.09 μg/g ww in lakes in the upper YRB 

(Braune and others, 1999). These concentrations were similar 

to 2002 northern pike concentrations. Kidd and others (1998) 

measured concentrations of PCBs in longnose sucker (0.011-

0.013 μg/g ww) and northern pike (<0.001-0.007 μg/g ww) 

muscle samples from YRB lakes within the Yukon Territory, 

Canada. Studies from the NCP (2003) reported concentrations 

of PCBs in burbot livers increased from 1990 to 1999 in the 

Canadian arctic. Mueller and Matz (2002) reported concentraμg/g 

0.1

0.075

0.05

0.025

0

301 302 303 304 305 306 307 308 309 310

Total PCBs Northern pike 

Longnose sucker 

Burbot 

Station 

Figure 11. Concentrations of total PCBs (μg/g ww) by station and 

species in whole body fish composite samples collected in the 

Yukon River Basin in 2002. Censored values are plotted as onehalf the LOD. Stations are ordered upstream to downstream. See 

Table 1 for station descriptions.

tions of PCBs in burbot livers were >0.11 μg/g ww in several 

YRB NWRs, and the greatest concentrations (0.27-1.4 μg/g 

ww) were found in burbot samples collected near Fairbanks.

Concentrations of total PCBs from 2002 were compared to laboratory-based toxicity tests and wildlife criteria. 

Concentrations of PCBs did not exceed the New York State 

Department of Environmental Conservation (NYSDEC) wildlife guideline for fish (0.11 μg/g ww) in any YRB fish sample 

(Fig. 11; Newell and others, 1987). Niimi (1996) as cited in 

Beyer and others (1996) determined that fish tissue concentrations of 100 μg/g ww can affect reproduction in females or be 

lethal, and concentrations of 50 μg/g ww can reduce growth 

and survival in offspring. Mink had inferior reproductive 

performance and offspring survival when fed Great Lakes 

fish or fish products with concentrations of PCBs of 0.48 μg/g 

ww (Hornshaw and others, 1983). Concentrations of PCBs in 

2002 YRB fish samples were below these thresholds.

H4IIE Bioassay

Dioxin-like activities in 31 composite samples were 

analyzed from 10 YRB stations. All samples had TCDD-EQ 

≤LOD (1.0 pg/g), which indicates the YRB samples did not 

have dioxin-like activity. A previous study from the YRB 

determined dioxins <LOD in northern pike and burbot (Snyder-Conn, 1992).

Previous studies have examined TCDD-EQ levels in 

wildlife. Most of the TCDD-EQ levels in fish from the YRB 

are less than those reported in fish from reference sites in 

previous studies (Giesy and others, 1995; Schmitt and others, 

2002a; van den Heuvel and others, 1995). The dietary threshold for toxicity of TCDD is 4.4 pg/g for mammals (Heaton and 

others, 1995; Tillitt and others, 1996) and approximately 5 pg/
39

g for avian wildlife (Nosek and others, 1992). YRB samples 

did not approach 35 pg/g, the threshold for toxic effects in fish 

(Schmitt and others, 2002a; Walker and others, 1996; Whyte 

and others, 2004).

Ethoxyresorufin O-Deethylase (EROD) Activity

EROD activity can be influenced by numerous factors 

including species (Addison and others, 1991; Segner and others, 1995), fish size and age (Khan and Payne, 2002a; Peters 

and Livingstone, 1995; Pluta, 1993), nutrition (Ankley and 

others, 1989), reproductive status (Campbell and others, 1976; 

Schreck and Hopwood, 1974), water temperature (Khan and 

Payne, 2002b; Machala and others, 1997), and capture activity 

(Machala and others, 1997). EROD activity can also vary 

among fish species, between genders, and among developmental stages of reproduction (Whyte and others, 2000). An 

ANOVA model containing the factors station, gender, and 

gonadal stage was not significant for northern pike or longnose sucker in the YRB (Table 13). Analysis of the entire 

BEST LRMN data set, which spanned a wider range of EROD 

values, indicated that gender was significant for most fish species including longnose sucker (BEST Program, unpublished 

data). Therefore, EROD activity was tabulated and evaluated 

by gender for northern pike and longnose sucker. 

EROD in Northern Pike

Mean EROD activity in female northern pike was greatest 

(8.57 pmol/min/mg) at Station 301 (n=4), and EROD activity 

ranged from 7.1 to 10.2 pmol/min/mg in individual fish from 

this station (Fig. 12; Table 14). All other geometric station 

means for female northern pike were <7.8 pmol/min/mg. 

A female pike from Station 306 had the maximum EROD 

activity (20.7 pmol/min/mg). Previous studies examining 

EROD activity in northern pike are limited. Williams and 

others (1997) determined basal EROD activity in female 

northern pike from western Canada to be 10-30 pmol/min/mg 

(as reviewed by Whyte and others, 2000). EROD activity in 

female northern pike ranged from 0.6 to 0.9 pmol/min/mg 

in the MRB (Schmitt and others, 2002a) and 0.14 to 1.77 

pmol/min/mg in the RGB (Schmitt and others, 2004). Most 

individual female northern pike (83%) in the YRB had EROD 

activities <10 pmol/min/mg in our study.

Mean EROD activity in male northern pike was greatest (17.5 pmol/min/mg) at Station 301 (n=2), with individual 

EROD values of 11.1-27.6 pmol/min/mg (Fig. 12; Table 14). 

All other geometric station means for male northern pike were 

<10.9 pmol/min/mg. Few studies have examined EROD activity in northern pike. Male northern pike had EROD activity 

range from 1.1 to 2.7 pmol/min/mg in the MRB (Schmitt and 

others, 2002a) and 0.18 to 2.30 pmol/min/mg in the RGB 

(Schmitt and others, 2004). EROD activity in male northern 

pike from western Canada was determined to be 30-45 pmol/

Results and Discussion

min/mg (Williams and others, 1997), which is greater than the 

maximum EROD activity calculated for male northern pike in 

2002.

EROD in Longnose Sucker

Mean EROD activity in female longnose sucker was 

greatest (8.78 pmol/min/mg) at Station 301, and EROD activity ranged from 5.1 to 14.5 pmol/min/mg in individual fish 

from this station (Fig. 12; Table 14). All other geometric 

station means for female longnose sucker were <7.1 pmol/

min/mg. Mean EROD activities in male longnose sucker were 

comparable to females with the greatest (10.0 pmol/min/mg) 

activity measured at Station 301 (n=1) (Table 14). All other 

geometric station means for male longnose sucker were <9.6 

pmol/min/mg.

Studies determining basal EROD activities for longnose sucker are limited. Longnose sucker from the YRB had 

similar EROD activities to female (2.4-11.0 pmol/min/mg) and 

male (7.3-18.0 pmol/min/mg) longnose sucker from the CRB 

(Hinck and others, 2004). Largescale sucker (Catostomus 

macrocheilus) from the CRB had station means >15 pmol/

min/mg, which were greater than EROD activities in YRB 

longnose sucker (Hinck and others, 2004). White sucker and 

longnose sucker have reported EROD activities ranging from 5 

to 15 pmol/min/mg (Whyte and others, 2000). EROD activity 

was measured in white sucker from the Mississippi River near 

Little Falls, Minnesota (Schmitt and others, 2002a). Activities 

range from 1.0 to 13.1 pmol/min/mg in females and 1.4 to 3.4 

pmol/min/mg in males (Schmitt and others, 2002a), which are 

similar to the EROD rates mesured in YRB longnose sucker. 

Others studies have reported that EROD activities range from 

8.5 to 10 pmol/min/mg in white sucker from reference or 

uncontaminated sites (Coulliard and Hodson, 1996; Schrank 

and others, 1997). White sucker from a site contaminated 

by PCBs, PAHs, and heavy metals had a mean EROD activity of 35.2 pmol/min/mg (Schrank and others, 1997). Four 

individual longnose sucker (<9%) from Stations 305 and 308 

in our study had EROD activities >15 pmol/min/mg (Fig. 

12). EROD activities in longnose sucker from the YRB are 

less than or equal to activities measured in longnose sucker at 

reference or uncontaminated sites in other studies.

EROD in Burbot

Hepatic EROD activity was measured in burbot from 

Stations 305 and 310. Mean station EROD activities in female 

and male burbot from Station 305 were 1.3 and 7.0 pmol/min/

mg, respectively. One male burbot from Station 310 had an 

EROD activity of 2.6 pmol/min/mg. These values are less 

than EROD activities reported in several Canadian studies 

(Kloepper-Sams and Benton, 1994; Lockhart and Metner, 

1992; Williams and others, 1997) reviewed in Whyte and others (2000) that reported basal EROD activities for burbot to be 

>10 pmol/min/mg.
40 Environmental Contaminants and their Effects on Fish

Table 13. Results of preliminary analysis of variance investigating the effects of various factors on 

biomarker responses in northern pike and longnose sucker in the Yukon River Basin in 2002. Shown are 

degrees-of-freedom (df), F-values with levels of significance (*0.01<P�0.05; **P�0.01), and coefficients of 

determination (R2

). aOnly female fish include in analysis. ND, not determined.—Continued 

Variable, Source, and 

(Transformation) 

Northern Pike 

df F R2 df 

Longnose Sucker 

F R2 

EROD (log) 

Model 31 3.71** 0.49 13 2.07* 0.46 

Station 6 0.86 3 0.71 

Gender 1 0.36 1 3.24 

Station*Gender 5 0.80 0 1.07 

Stage 1 0.66 1 0.06 

Stage*Station 6 0.80 3 1.11 

Stage*Gender 1 0.89 1 3.95 

Stage*Station*Gender 5 0.70 0 ND 

Error 122 31 

Condition Factor 

Model 32 5.32** 0.58 13 3.69** 0.61 

Station 7 7.33** 3 1.27 

Gender 1 0.61 1 3.54 

Station*Gender 5 2.66* 0 0.32 

Stage 1 1.51 1 1.13 

Stage*Station 7 3.81** 3 2.14 

Stage*Gender 1 1.84 1 3.09 

Stage*Station*Gender 5 3.04* 0 ND 

Error 122 31 

Splenosomatic Index 

Model 18 2.24** 0.23 8 1.44 0.24 

Station 9 2.53* 4 2.16 

Gender 1 7.81** 1 0.10 

Station*Gender 8 1.45 3 0.28 

Error 137 36 

Hepatosomatic Index 

Model 18 0.79 0.09 ND ND ND 

Station 9 0.74 ND 

Gender 1 0.53 ND 

Station*Gender 8 0.80 ND 

Error 136 ND 

HAI (rank) 

Model 32 4.88** 0.51 13 0.68 0.24 

Station 7 3.91** 3 1.16 

Gender 1 1.03 1 0.06 

Station*Gender 5 0.86 0 1.32 

Stage 1 0.43 1 2.00 

Stage*Station 7 0.78 3 1.14 

Stage*Gender 1 1.92 1 0.38 

Stage*Station*Gender 5 1.26 0 ND 

Error 121 28 
Results and Discussion 41

Table 13. Results of preliminary analysis of variance investigating the effects of various factors on 

biomarker responses in northern pike and longnose sucker in the Yukon River Basin in 2002. Shown are 

degrees-of-freedom (df), F-values with levels of significance (*0.01<P�0.05; **P�0.01), and coefficients of 

determination (R2

). aOnly female fish include in analysis. ND, not determined.—Continued 

Variable, Source, and 

(Transformation) 

Northern Pike 

df F R2 df 

Longnose Sucker 

F R2 

MA-% (log) 

Model 37 1.13 0.48 14 1.13 0.35 

Station 9 0.06 4 0.96 

Gender 1 1.15 1 0.22 

Station*Gender 8 6.36* 0 ND 

Age 1 0.91 1 0.00 

Age*Station 9 0.08 4 0.58 

Age*Gender 1 1.02 1 0.34 

Age*Station*Gender 8 0 ND 

Error 100 29 

MA-size (log) 

Model 37 1.79* 0.40 14 1.61 0.44 

Station 9 0.52 4 1.42 

Gender 1 0.79 1 1.24 

Station*Gender 8 0.57 0 ND 

Age 1 1.86 1 0.17 

Age*Station 9 0.47 4 1.07 

Age*Gender 1 0.65 1 1.27 

Age*Station*Gender 8 0.40 0 ND 

Error 100 29 

MA-# 

Model 37 1.55* 0.36 14 1.50 0.42 

Station 9 1.40 4 3.12* 

Gender 1 0.01 1 0.04 

Station*Gender 8 0.65 0 ND 

Age 1 1.68 1 2.03 

Age*Station 9 0.66 4 0.60 

Age*Gender 1 0.31 1 0.00 

Age*Station*Gender 8 0.56 0 ND 

Error 100 

Gonadosomatic Index 

Model 32 26.8** 0.88 13 2.31* 0.49 

Station 7 0.33 3 0.20 

Gender 1 0.07 1 0.15 

Station*Gender 5 0.10 0 0.32 

Stage 1 0.97 1 0.45 

Stage*Station 7 1.46 3 0.17 

Stage*Gender 1 0.29 1 0.05 

Stage*Station*Gender 5 0.09 0 ND 

Error 122 31 
42 Environmental Contaminants and their Effects on Fish

Table 13. Results of preliminary analysis of variance investigating the effects of various factors on 

biomarker responses in northern pike and longnose sucker in the Yukon River Basin in 2002. Shown are 

degrees-of-freedom (df), F-values with levels of significance (*0.01<P�0.05; **P�0.01), and coefficients of 

determination (R2

). aOnly female fish include in analysis. ND, not determined.—Continued 

Variable, Source, and 

(Transformation) 

Northern Pike 

df F R2 df 

Longnose Sucker 

F R2 

Vitellogenin (log) 

Model 28 6.85** 0.65 13 7.28** 0.76 

Station 5 0.64 3 0.72 

Gender 1 0.22 1 0.71 

Station*Gender 4 0.89 0 1.53 

Stage 1 1.77 1 2.57 

Stage*Station 6 0.32 3 0.28 

Stage*Gender 1 1.30 1 0.02 

Stage*Station*Gender 4 1.59 0 ND 

Error 105 31 

Estradiol 

Model 28 3.31** 0.47 13 3.54** 0.60 

Station 5 0.51 3 1.85 

Gender 1 0.04 1 6.49* 

Station*Gender 4 1.72 0 1.86 

Stage 1 2.08 1 9.16* 

Stage*Station 5 0.24 3 1.82 

Stage*Gender 1 0.16 1 0.12 

Stage*Station*Gender 4 1.46 0 ND 

Error 103 31 

11-ketotestosterone 

Model 28 4.03** 0.52 13 1.50 0.39 

Station 5 3.38** 3 1.10 

Gender 1 5.52* 1 2.30 

Station*Gender 4 2.04 0 0.10 

Stage 1 6.15* 1 2.17 

Stage*Station 5 2.84 3 0.80 

Stage*Gender 1 1.66 1 0.06 

Stage*Station*Gender 4 1.31 0 ND 

Error 103 31 

Estradiol/11-ketotestosterone 

Model 28 1.71* 0.32 13 2.28* 0.49 

Station 5 0.54 3 2.71 

Gender 1 0.86 1 9.68** 

Station*Gender 4 0.76 0 1.19 

Stage 1 1.91 1 7.58** 

Stage*Station 5 0.71 3 2.29 

Stage*Gender 1 0.23 1 1.13 

Stage*Station*Gender 4 0.91 0 ND 

Error 103 31 
Results and Discussion 43

Table 13. Results of preliminary analysis of variance investigating the effects of various factors on 

biomarker responses in northern pike and longnose sucker in the Yukon River Basin in 2002. Shown are 

degrees-of-freedom (df), F-values with levels of significance (*0.01<P�0.05; **P�0.01), and coefficients of 

determination (R2

). aOnly female fish include in analysis. ND, not determined.—Continued 

Variable, Source, and 

(Transformation) 

Atresia a 

Model 30 1.21 0.44 13 0.46 0.26 

Station 3 0.48 0 ND 

Stage 1 0.14 1 0.00 

Stage*Station 3 0.04 0 ND 

Age 1 0.11 1 0.00 

Age*Station 3 0.50 0 ND 

Stage*Age 1 0.01 1 0.00 

Stage*Age*Station 3 0.18 0 ND 

Error 46 17 

Northern Pike 

df F R2 df 

Longnose Sucker 

F R2 

Accumulative Contaminants, H4IIE, and EROD:

Summary

Concentrations of all contaminants except Hg and Se 

measured in YRB fish samples were low. Concentrations of 

Hg were >0.3 μg/g ww in northern pike from Stations 304, 

306, 307, and 308 and in burbot from Station 305. Concentrations of Hg >0.3 μg/g ww in fish have been shown to cause 

reproductive impairment in loons (Barr, 1986). Fish from 

Stations 301, 302, 304, and 305 had concentrations of Se >0.6 

μg/g ww, which may be toxic to piscivorous wildlife (Lemly, 

1996). Other inorganic and organic chemicals were either 

<LOD or below wildlife or other threshold criteria. Comparison of 2002 concentrations with historical NCBP data 

revealed that most organochlorine and elemental contaminants 

were decreasing, continuing a two-decade trend for accumulative contaminants in the YRB. Dioxin-like contaminants, as 

indicated by the H4IIE rat hepatoma cell bioassay, were ≤LOD 

in YRB fish samples. The results are consistent with previous 

dioxin studies in the basin.

EROD results were not consistent with H4IIE results, 

indicating fish were exposed to EROD-inducing chemicals 

other than PCBs and dioxins. Results of the EROD assay 

determined that northern pike and longnose sucker from Station 301 had the greatest EROD activities compared to other 

stations, although these activities were less than basal rates 

estimated from other studies for these species. EROD data for 

burbot were limited to a small number of individuals, but these 

values were similar to EROD activities measured in this species from other reference studies. EROD activities in northern 

pike, longnose sucker, and burbot did not indicate exposure to 

PAHs or PHHs.

Fish Health Indicators

Organism-Level Indicators

External Gross Lesions

External gross abnormalities were identified in the field 

during the fish health examination (Schmitt and Dethloff, 

2000). The fish health assessment determined that 45% of 

all fish collected from the YRB had external gross lesions 

(abnormalities) (Table 15). These lesions were categorized 

by location including the body surface, eyes, opercles, and 

fins. The percentage of fish with external lesions ranged from 

23% at Station 309 to 91% at Station 303 (Table 15). Statistical analyses determined that male and female northern pike, 

longnose sucker, and burbot did not differ significantly in the 

occurrence of external lesions; therefore, genders were combined. The percentage of burbot with lesions (<8%) was less 

than the basinwide percentage for all species, although there 

were fewer burbot collected than northern pike or longnose 

sucker. The basinwide percentage of northern pike (51%) and 

longnose sucker (41%) with lesions were comparable. The 

percent of lesions was high (>50%) in fish at some stations, 

but caution needs to be used when interpreting these data. 

Most lesions were attributed to cuts or abrasions on the body 

surface of the fish, which are frequently observed in predatory 

fish like northern pike. Many of these were not considered 

to be a result of exposure to environmental contaminants but 

were more likely due to collection and holding time prior to 

fish processing or normal wear as the fish ages. Pieces of 

tissue from lip or body lesions of northern pike (n=6) and 

longnose sucker (n=1) were examined histologically. These 

lesions were composed of dermal, subdermal, and intramus-
44 Environmental Contaminants and their Effects on Fish

25

20

15

10

5

0

30

25

20

15

10

5

0

18

14

10

6

2

0

25

20

15

10

5

0

301 302 303 304 305 306 307 308 309 310

Northern pike-female 

Northern pike-male 

Longnose sucker-female 

Longnose sucker-male 

Station 

Figure 12. Hepatic microsomal EROD activity (pmol/min/mg) by 

station in female and male northern pike and longnose sucker 

collected in the Yukon River Basin in 2002. Shown for each group 

are points representing individual fish and the mean (red horizontal line), median (black horizontal line), interquartile range (box), 

and the 10th and 90th percentiles (whiskers). Stations are ordered 

upstream to downstream. See Table 1 for station descriptions.

pmol/min/mg pmol/min/mg pmol/min/mg pmol/min/mg

cular chronic inflammatory infiltrates for which an eliciting 

agent was not observed. White nodules on the fins of another 

longnose sucker were determined to be areas of hypertrophy 

and hyperplasia of epidermal cells.

Health Assessment Index

The health assessment index (HAI) is a systematic 

method used to identify external and internal abnormalities for 

individual fish during the field health assessment. A higher 

HAI score indicates a greater number of lesions were identified on the fish. The HAI may vary depending on gender and 

gonadal stage of development. Neither gender nor gonadal 

stage influenced HAI in northern pike or longnose sucker 

(Table 13). Therefore, the HAI scores for both genders were 

combined for analysis.

HAI scores were evaluated for 156 northern pike from 

the YRB. Most HAI scores for northern pike (80%) ranged 

from 0 to 70 (Table 16). Mean HAI scores in northern pike 

ranged from 10 to 67 for all stations except Station 303, which 

had a mean HAI of 92.3 in northern pike (Table 16). Stations 

304, 306, and 307 also had multiple fish with HAI scores >100 

with most lesions attributed to abnormalities of the liver, kidney, gill, and fins. HAI scores for northern pike from Garrison 

Dam, North Dakota in the MRB ranged from 0-60 (Schmitt 

and others, 2002a), and those from Alamosa, Colorado in the 

RGB ranged from 40-110 (Schmitt and others, 2004). Other 

studies evaluating HAI scores in northern pike were not found.

HAI scores were evaluated in 43 longnose sucker and 

were consistent among YRB stations. Most HAI scores for 

longnose sucker (79%) ranged from 0 to 50, indicating most 

longnose sucker were identified as having zero to two gross 

lesions (Table 16). Station means of HAI scores in longnose 

sucker ranged from 29 to 36 with the exception of Station 304 

(70). All HAI scores in longnose sucker from the YRB were 

≤100. HAI values from the YRB generally were <HAI values 

for longnose and largescale sucker from the CRB (Hinck and 

others, 2004; Tetra Tech Inc., 1996). Other studies evaluating 

HAI in longnose sucker were not found.

Condition and Organosomatic Indices

These indices are considered general indicators of the 

overall health of the fish, and alterations of these indices may 

indicate the effects resulting from exposure to contaminants 

(Schmitt and Dethloff, 2000). Factors such as gender or 

gonadal stage can affect these indices. 

Condition and Organosomatic Indices in Northern Pike

Station and gender influenced splenosomatic index 

(SSI) and condition factor (CF) but not hepatosomatic index 

(HSI) in northern pike (Table 13). Interactions between 
Results and Discussion 45

Table 14. Geometric mean and range of microsomal EROD activities (pmol/min/mg protein) in fish collected in the Yukon River 

Basin in 2002. Censored values were represented by one half the LOQ in the computation of geometric means. Fish in which gender 

was undetermined or no gonad was obtained are listed as juvenile. The maximum geometric station mean is shown in bold for each 

taxon. Stations are listed upstream to downstream. 

Species and Station 

Female 

n 

Male 

n 

Juvenile 

Range Mean Range Mean n Range Mean 

Northern pike

Charley-Kandik, AK (301) 4 7.07-10.2 8.57 2 11.1-27.6 17.51 0 -- --

Fish Hook Bend, AK (302) 15 0.90-13.0 2.70 5 4.84-25.8 9.96 0 -- --

Fort Yukon, AK (303) 11 2.60-13.4 7.82 11 5.39-22.7 10.87 0 -- --

The Bridge, AK (304) 7 2.88-13.3 6.36 2 4.88-7.80 6.17 0 -- --

Fairbanks, AK (305) 3 0.71-0.71 0.71 0 -- -- 1 -- 3.50 

Tolovana, AK (306) 10 1.17-20.7 6.54 10 1.86-11.3 6.06 0 -- --

Tanana, AK (307) 12 0.44-19.5 3.62 8 3.02-13.5 5.79 0 -- --

Galena, AK (308) 8 3.35-12.8 7.19 12 3.93-9.42 5.58 0 -- --

Innoko, AK (309) 9 0.64-7.9 2.84 11 0.64-26.8 4.12 0 -- --

Kotlik, AK (310) 9 0.42-3.5 1.38 8 0.96-7.69 3.13 0 -- --

Longnose sucker 

Charley-Kandik, AK (301) 11 5.09-14.5 8.78 1 -- 10.03 0 -- --

The Bridge, AK (304) 2 2.82-9.58 5.19 0 -- -- 0 -- --

Fairbanks, AK (305) 9 2.44-8.93 5.12 11 4.49-23.1 9.59 1 -- 15.27 

Tolovana, AK (306) 2 4.03-4.40 4.21 1 -- 3.95 0 -- --

Galena, AK (308) 7 3.82-16.1 7.05 1 -- 3.56 0 -- --

Burbot 

Fairbanks, AK (305) 8 0.23-9.93 1.27 4 3.06-19.1 7.03 0 -- --

Kotlik, AK (310) 0 -- -- 1 -- 2.55 0 -- --

gender and station and stage and station were significant, means for female northern pike were greatest at Stations 306, 

but neither variable was significant alone. Therefore, data 308, and 310, as indicated by the station being a significant 

for male and female northern pike were examined separately factor in the ANOVA model (Table 13). Most female northern 

only for SSI so as not to confound the potential effects other pike (94%) had SSI between 0.05 and 0.10%. In previous 

variables may have on the fish health indicators with the studies, female northern pike from the MRB (0.09-0.11%; 

effects caused by gender or stage. The basinwide mean CF in Blazer and others, 2002) and RGB (0.08-0.26%; Schmitt and 

northern pike was 0.59, and station means ranged from 0.51 at others, 2004) had similar SSI to those measured in the YRB.

Station 303 to 0.67 at Station 307 (Table 17; Fig. 13). Condi- SSI in male northern pike was greater than in female 

tion factor for all individual northern pike from the YRB was northern pike with a basinwide mean of 0.13%, and station 

<0.78. Similar CF were reported in northern pike from the means ranged from 0.10% at Station 303 to 0.18% at Station 

MRB (Blazer and others, 2002) and RGB (Schmitt and others, 301 (Table 18; Fig. 13). SSI in male northern pike (SE=0.007) 

2004). Other studies evaluating CF in northern pike were not varied more than in female northern pike (SE=0.004), with 

found. individual SSI values ranging from 0.04 to 0.29% (Table 

Northern pike have discrete livers, unlike longnose 18). Most male northern pike (85%) had SSI between 0.06 

sucker, and therefore HSI was calculated. The basinwide to 0.20%. Male northern pike from the MRB (0.11-0.24%; 

mean HSI for northern pike was 1.8% (Table 17). Station Blazer and others, 2002) and RGB (0.08-0.24%; Schmitt and 

means for HSI in northern pike ranged from 1.1% at Station others, 2004) had similar SSI to those measured in the YRB.

309 to 3.3% at Station 310 (Table 17; Fig. 13). All stations 

except Station 310 had mean HSI <2.2%. HSI >3.0% were 

calculated for fish at Stations 306, 307, and 310; however, Condition and Organosomatic Indices in Longnose Sucker

most northern pike (81%) had HSI between 0.7 and 2.5% (Fig. 

13). Station 310 was the only station that consistently had fish Neither gender nor developmental stage influenced fish 

with HSI >2.5%. HSI for individual northern pike from the health indicators in longnose sucker (Table 13). Therefore, the 

YRB were greater than those calculated in northern pike from data were combined for statistical analysis.

the MRB (1.7-2.8%; Blazer and others, 2002) and RGB (0.7- Condition factor in longnose sucker was generally greater 

2.6%; Schmitt and others, 2004). HSI data for northern pike than in northern pike in the YRB. The basinwide mean for 

from other studies were not found. CF in longnose sucker was 0.81 (Table 17). Longnose sucker 

SSI in male and female northern pike were examined sep- from Station 308 had the greatest mean CF (0.94), and other 

arately. The basinwide mean for SSI in female northern pike station means ranged from 0.76 to 0.86 (Table 17). The CF 

was 0.11%, and station means ranged from 0.09% at Station values did not differ significantly among stations (Table 13). 

309 to 0.14% at Station 306 (Table 18; Fig. 13). SSI station Individual fish CF values ranged from 0.63 to 1.10 with 78% 
46 Environmental Contaminants and their Effects on Fish

Table 15. Number and location of external lesions identified on fish collected in the Yukon River Basin in 

2002. Body, eyes, opercles, and fins of each fish were examined for the presence of lesions, and the 

proportion of fish with lesions was calculated. Stations are listed upstream to downstream. 

Lesion Location 

Station and Species n Body Eyes Opercles Fins Proportion

Total no. 

w/lesions 

Charley-Kandik, AK (301) 

All 18 8 0 1 0 8 0.444 

Northern pike 6 4 0 1 0 4 0.667 

Longnose sucker 12 4 0 0 0 4 0.333 

Fish Hook Bend, AK (302) 

All 20 7 0 0 0 7 0.350 

Northern pike 20 7 0 0 0 7 0.350 

Fort Yukon, AK (303) 

All 22 13 3 6 11 20 0.909 

Northern pike 22 13 3 6 11 20 0.909 

The Bridge, AK (304) 

All 11 4 0 5 0 8 0.727 

Northern pike 9 3 0 4 0 6 0.667 

Longnose sucker 2 1 0 1 0 2 1.000 

Fairbanks, AK (305) 

All 36 8 1 4 0 11 0.306 

Northern pike 3 1 0 0 0 1 0.333 

Longnose sucker 21 6 1 4 0 9 0.429 

Burbot 12 1 0 0 0 1 0.083 

Tolovana, AK (306) 

All 23 4 0 3 0 7 0.304 

Northern pike 20 4 0 1 0 5 0.250 

Longnose sucker 3 0 0 2 0 2 0.667 

Tanana, AK (307) 

All 20 13 1 0 0 13 0.650 

Northern pike 20 13 1 0 0 13 0.650 

Galena, AK (308) 

All 28 9 0 2 0 11 0.393 

Northern pike 20 7 0 2 0 9 0.450 

Longnose sucker 8 2 0 0 0 2 0.250 

Innoko, AK (309) 

All 21 4 0 2 0 5 0.238 

Northern pike 21 4 0 2 0 5 0.238 

Kotlik, AK (310) 

All 18 8 0 0 4 11 0.611 

Northern pike 17 8 0 0 4 11 0.647 

Burbot 1 0 0 0 0 0 0.000 

Basin Total 

All 217 78 5 23 15 101 0.465 

Northern pike 158 64 4 16 15 81 0.513 

Longnose sucker 46 13 1 7 0 19 0.413 

Burbot 13 1 0 0 0 1 0.077 

of longnose sucker having a CF between 0.70 and 0.90 (Fig. 

14). Condition factor in individual longnose sucker from 

the upper CRB ranged from 0.90 to 1.11 (Hinck and others, 

2004). The CF in largescale sucker from the CRB had station 

means that ranged from 0.86 to 1.2 and a basinwide mean of 

0.94 (Hinck and others, 2004). Longnose sucker collected 

from rivers in northern Alberta had CF ranging from 1.01 to 

1.32 (Oakes and others, 2004). Oakes and others (2004) also 

determined longnose sucker collected below municipal sewage 

and pulp mill effluents in the Wapiti River had significantly 

higher CF compared to upstream reference sites. The state of 

Minnesota set standards that considered white sucker with CF 

<1.0 to be in poor condition (Carlander, 1969).

SSI values in longnose sucker were greater than those 

measured in northern pike from the YRB. Mean SSI values in 

longnose sucker were similar among YRB stations although 

some individual values caused increased variability in the data. 

The basinwide mean SSI for longnose sucker was 0.24%, and 

the station means for longnose sucker ranged from 0.12% at 

Station 306 to 0.27% at Station 305 (Table 18). The majority 
4

7

Table 16. Distribution of Health Assessment Index (HAI) scores among northern pike, longnose sucker, and burbot collected in the Yukon River Basin in

2002. Arithmetic mean and standard error (SE) are also given. Station totals where HAI scores were not available for all individual fish are noted with an asterisk (*). 

H

0

AI Score 

Species and Station 10 30 40 50 60 70 90 100 130 160 Total Mean SE 

Northern pike

Charley-Kandik, AK (301) 1 0 0 3 0 0 2 0 0 0 0 6 43.3 10.5 Fish Hook Bend, AK (302) 0 0 10 0 0 7 0 2 0 0 0 19* 47.4 4.8 Fort Yukon, AK (303) 0 0 0 2 0 4 3 1 6 5 1 22 92.3 7.1 The Bridge, AK (304) 1 0 1 0 0 1 3 1 2 0 0 9 65.6 10.9 Fairbanks, AK (305) 2 0 1 0 0 0 0 0 0 0 0 3 10.0 10.0 Tolovana, AK (306) 0 0 3 5 0 3 6 0 3 0 0 20 59.5 5.2 Tanana, AK (307) 0 1 1 5 0 2 6 0 3 2 0 20 67.0 7.2 Galena, AK (308) 2 7 2 5 0 0 3 0 0 0 0 19* 28.4 5.4 Innoko, AK (309) 0 6 1 11 0 1 1 0 1 0 0 21 36.2 4.9 Kotlik, AK (310) 2 2 8 2 0 0 0 1 1 1 0 17 38.8 8.6 Total 8 16 27 33 0 18 24 5 16 8 1 156 

Longnose sucker

Charley-Kandik, AK (301) 3 2 3 2 0 1 0 0 1 0 0 12 29.2 8.5 The Bridge, AK (304) 0 0 0 1 0 0 0 0 1 0 0 2 70.0 30.0 Fairbanks, AK (305) 1 6 1 6 1 0 3 0 1 0 0 19* 36.3 6.2 Tolovana, AK (306) 0 1 0 1 1 0 0 0 0 0 0 3 33.3 12.0 Galena, AK (308) 1 3 0 1 0 0 2 0 0 0 0 7* 30.0 11.3 Total 5 12 4 11 2 1 5 0 3 0 0 43 

Burbot

Fairbanks, AK (305) 0 0 5 0 0 3 2 2 0 0 0 12 54.2 6.8 Kotlik, AK (310) 0 0 1 0 0 0 0 0 0 0 0 1 30.0 --Total 0 0 6 0 0 3 2 2 0 0 0 13 

ResultsandDiscussion
48 Environmental Contaminants and their Effects on Fish

Table 17. Arithmetic mean of condition factor (CF) and hepatosomatic index (HSI; %) by species and station in 

northern pike, longnose sucker, and burbot collected int he Yukon River Basin in 2002. Number of samples (n ), 

minimum (min.), maximum (max.), and standard error (SE) are also given. Stations are ordered upstream to 

downstream. The maximum station mean for each taxon is shown in bold. 

Species and Station Min. Max. SE Min. Max. SE

Hepatosomatic Index (HSI) 

n Mean

Condition Factor (CF) 

n Mean

Northern pike 

Basin Total 157 0.59 0.40 0.78 0.01 156 1.78 0.63 4.76 0.06 

Charley-Kandik, AK (301) 6 0.57 0.51 0.70 0.03 6 1.43 0.94 1.82 0.16 

Fish Hook Bend, AK (302) 20 0.55 0.49 0.67 0.01 18 1.19 0.90 2.43 0.08 

Fort Yukon, AK (303) 22 0.51 0.45 0.54 0.01 22 1.25 0.90 1.96 0.06 

The Bridge, AK (304) 9 0.57 0.40 0.66 0.03 9 1.99 1.12 2.68 0.19 

Fairbanks, AK (305) 3 0.57 0.44 0.71 0.08 3 1.94 1.50 2.40 0.26 

Tolovana, AK (306) 20 0.60 0.48 0.69 0.01 20 1.77 1.12 3.03 0.11 

Tanana, AK (307) 20 0.67 0.46 0.78 0.02 20 2.19 0.77 3.14 0.16 

Galena, AK (308) 20 0.62 0.51 0.68 0.01 20 1.80 1.16 2.52 0.08 

Innoko, AK (309) 20 0.55 0.46 0.74 0.02 21 1.14 0.63 2.93 0.12 

Kotlik, AK (310) 17 0.63 0.57 0.71 0.01 17 3.33 2.42 4.76 0.13 

Longnose sucker 

Basin Total 46 0.81 0.63 1.10 0.01 -- -- -- -- --

Charley-Kandik, AK (301) 12 0.76 0.66 0.89 0.02 -- -- -- -- --

The Bridge, AK (304) 2 0.86 0.85 0.88 0.01 -- -- -- -- --

Fairbanks, AK (305) 21 0.80 0.65 0.91 0.02 -- -- -- -- --

Tolovana, AK (306) 3 0.76 0.63 0.83 0.07 -- -- -- -- --

Galena, AK (308) 8 0.94 0.86 1.10 0.03 -- -- -- -- --

Burbot 

Basin Total 13 0.56 0.43 0.75 0.02 13 5.78 2.90 9.77 0.59 

Fairbanks, AK (305) 12 0.56 0.43 0.75 0.02 12 5.70 2.90 9.77 0.64 

Kotlik, AK (310) 1 0.60 -- -- -- 1 6.77 -- -- --

(80%) of longnose sucker had SSI between 0.15 and 0.40%, of aggregates per mm2 (MA-#), mean size of aggregates in 

and all SSI >0.33% were calculated for fish from Station 305 μm2 (MA-size), and percent of tissue occupied by macrophage 

(Fig. 14). The BEST LRMN collected longnose and larges- aggregates (MA-%) were analyzed for northern pike, longnose 

cale sucker in the CRB in 1997 (Hinck and others, 2004). The sucker, and burbot from the YRB. Gender and age have been 

basinwide SSI mean for CRB largescale sucker was 0.25% reported to influence macrophage aggregate parameters in 

with station means ranging from 0.17 to 0.37%, and individual various species (Blazer and others, 2002; Hinck and others, 

SSI values for longnose sucker were 0.02-0.39% (Hinck and 2004; Schmitt and others, 2004); therefore, ANOVAs using 

others, 2004). SSI values from the YRB were similar to those these factors for each species were examined to determine if 

calculated in the CRB. these factors affected MA data in northern pike and longnose 

sucker in the YRB.

Cellular and Histopathological Indicators MA-# 

Splenic macrophage aggregates were quantified and mea- Neither gender nor age influenced MA-# in northern pike 

sured and are described in the following paragraphs. Gonadal and longnose sucker (Table 13); therefore, genders were com- tissue was examined microscopically and is described in a bined for data analysis. The basinwide mean MA-# for north- later section devoted to reproductive biomarkers. ern pike was 3.7 MA/mm2

, and station means for northern 

pike ranged from 2.7 MA/mm2 at Station 308 to 5.2 MA/mm2

at Station 306 (Table 19). Individual MA-# in northern pike 

Macrophage Aggregates ranged from 0.0 to 12.9 MA/mm2

 (Fig. 15). MA-# were >10 

Macrophage aggregates are believed to house endogenous MA/mm2

 in northern pike from Stations 302, 303, and 306. 

and exogenous waste products and are active in the immune Most northern pike (94%) had MA-# <8.0 MA/mm2

, and MAresponses to these materials (Schmitt and Dethloff, 2000). # did not differ significantly among stations (Table 13). Other 

Three macrophage aggregate parameters, density or number studies reporting MA-# data for northern pike were not found.

MA-# in longnose sucker were greater than in northern 
49

%

%

%

1.0

0.8

0.6

0.4

0.2

0.0

6

5

4

3

2

1

0

0.30

0.25

0.20

0.15

0.10

0.05

0.00

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

CF

HSI

SSI-female

SSI-male

301 302 303 304 305 306 307 308 309 310

Station

Figure 13. Fish health indicators by station in female and male 

northern pike collected in the Yukon River Basin in 2002. Indicators include condition factor (CF), hepatosomatic index (HSI), 

and splenosomatic index (SSI). Females and males were plotted 

separately when analysis of variance modeling determined gender was a significant factor. Shown for each group are points representing individual fish and the mean (red horizontal line), median 

(black horizontal line), interquartile range (box), and the 10th and 

90th percentiles (whiskers). Stations are ordered upstream to 

downstream. See Table 1 for station descriptions.

Results and Discussion

pike in the YRB. The basinwide mean MA-# for longnose 

sucker was 5.5 MA/mm2, and station means ranged from 2.4 

MA/mm2 at Station 308 to 11.5 MA/mm2 at Station 304 (Table 

19). Individual MA-# for longnose sucker ranged from 0.0 

to 21.2 MA/mm2 with the majority (70%) having MA-# of 

1.0-10.0 MA/mm2 (Fig. 16). Five fish from Stations 301, 304, 

and 305 had MA-# values >12.0 MA/mm2. MA-# differed 

significantly among stations for longnose sucker (Table 13). 

Previous studies on MA-# in longnose sucker have not been 

documented. Hinck and others (2004) reported mean station MA-# to range from 4.9 to 8.7 MA/mm2

 and a basinwide 

mean of 6.8 MA/mm2 in largescale sucker in the CRB. 

MA-# data for burbot were only available for Station 

305 (Table 19). The station mean was 3.9 with a range of 

0.6-8.8 MA/mm2. These data were similar to MA-# values 

for northern pike and longnose sucker, although other studies 

documenting MA-# in burbot were not located.

MA-Size 

Gender and age did not influence MA-size in northern 

pike or longnose sucker (Table 13); therefore, genders were 

combined for data analysis. The basinwide mean MA-size for 

northern pike was 1,134 μm2 with station means ranging from 

849 μm2 at Station 304 to 1,333 μm2 at Station 307 (Table 19). 

Most northern pike (92%) had MA-size ranging from 200 to 

2,000 μm2 (Fig. 15). These data did not support that MA-size 

varied significantly among stations for northern pike (Table 

13). MA data in northern pike from other studies were not 

found.

In general, MA-size was greater in longnose sucker than 

in northern pike, with longnose sucker having a basinwide 

mean of 2,095 μm2 (Table 19). MA-size station means for 

longnose sucker ranged from 1,486 μm2 at Station 308 to 2,672 

μm2 at Station 301, and individual MA-size in longnose sucker 

ranged from 0 to 8,201 μm2 (Table 19; Fig. 16). Stations 301, 

305, and 308 had MA-size in longnose sucker >4,000 μm2, 

but most longnose sucker (71%) had MA-size of 500-3,000 

μm2 (Fig. 16). As in northern pike, MA-size did not vary 

significantly among stations for longnose sucker (Table 13). 

MA-size data for longnose sucker from other studies were 

not found. However, largescale sucker from the CRB had a 

basinwide mean MA-size of 3,580 μm2 with the station means 

ranging from 2,821 to 4,941 μm2 (Hinck and others, 2004). 

The CRB data for largescale sucker is slightly greater than 

MA-size data for longnose sucker in the YRB.

MA-size data for burbot were only available for Station 

305. The station mean for MA-size in burbot was 62,860 

μm2 with individual values ranging from 368 to 250,000 μm2

(Table 19). The MA-size data in burbot were greater than any 

data measured by the BEST Program, although MA parameters can vary by species (Schmitt and Dethloff, 2000). No 

other studies examining MA-size in burbot were available for 

comparison to YRB data.
50 Environmental Contaminants and their Effects on Fish

Table 18. Arithmetic mean of splenosomatic index (SSI; %) by species, gender, and station in 

northern pike, longnose sucker, and burbot collected in the Yukon River Basin in 2002. Number of 

samples (n ), minimum (min.), maximum (max.), and standard error (SE) are also given. Stations are 

ordered upstream to downstream. The maximum station mean for each taxon is shown in bold. 

Species, Gender, and Station 

Northern pike 

Female 

Basin Total 88 0.113 0.033 0.240 0.004 

Charley-Kandik, AK (301) 4 0.098 0.054 0.114 0.015 

Fish Hook Bend, AK (302) 15 0.108 0.080 0.139 0.006 

Fort Yukon, AK (303) 11 0.099 0.033 0.217 0.014 

The Bridge, AK (304) 7 0.101 0.077 0.142 0.008 

Fairbanks, AK (305) 3 0.098 0.081 0.118 0.011 

Tolovana, AK (306) 10 0.148 0.077 0.240 0.019 

Tanana, AK (307) 12 0.102 0.049 0.179 0.010 

Galena, AK (308) 8 0.143 0.079 0.197 0.013 

Innoko, AK (309) 9 0.093 0.078 0.119 0.005 

Kotlik, AK (310) 9 0.125 0.083 0.181 0.010 

Male 

Basin Total 68 0.130 0.041 0.291 0.007 

Charley-Kandik, AK (301) 2 0.180 0.153 0.206 0.027 

Fish Hook Bend, AK (302) 4 0.151 0.095 0.233 0.029 

Fort Yukon, AK (303) 11 0.101 0.055 0.183 0.011 

The Bridge, AK (304) 2 0.137 0.135 0.139 0.002 

Tolovana, AK (306) 10 0.118 0.066 0.191 0.012 

Tanana, AK (307) 8 0.142 0.094 0.191 0.013 

Galena, AK (308) 12 0.162 0.091 0.278 0.017 

Innoko, AK (309) 11 0.105 0.041 0.291 0.023 

Kotlik, AK (310) 8 0.135 0.067 0.270 0.023 

Longnose sucker 

Basin Total 46 0.237 0.017 0.448 0.014 

Charley-Kandik, AK (301) 12 0.240 0.151 0.326 0.017 

The Bridge, AK (304) 2 0.176 0.082 0.269 0.094 

Fairbanks, AK (305) 21 0.274 0.017 0.448 0.023 

Tolovana, AK (306) 3 0.123 0.103 0.151 0.014 

Galena, AK (308) 8 0.194 0.126 0.250 0.012 

Burbot 

Basin Total 13 0.067 0.046 0.098 0.005 

Fairbanks, AK (305) 12 0.069 0.049 0.098 0.005 

Kotlik, AK (310) 1 0.046 -- -- --

n Mean Min. Max. SE

MA-% 

Gender and age did not influence MA-% in northern pike 

and longnose sucker (Table 13); therefore, genders were combined for data analysis. The basinwide mean MA-% in northern pike was 0.43% with station means ranging from 0.31% 

at Station 310 to 0.59% at Station 305 (Table 19). Station 

305 also had the greatest MA-# for northern pike. Individual 

MA-% in northern pike ranged from 0 to 1.78% in the YRB 

(Fig. 15), and MA-% did not vary significantly among stations 

(Table 13). MA-% data in northern pike from other studies 

were not found.

The percent tissue occupied by MA was greater in 

longnose sucker compared to northern pike in the YRB with 

a basinwide mean of 1.26% (Table 19). Station means ranged 

from 1.04% at Station 304 to 1.78% at Station 301 in longnose 

sucker (Table 19; Fig. 16), but station means were not significantly different (Table 13). Four female longnose sucker 

from Stations 305 and 308 had MA-% >3.0%, whereas most 

longnose sucker (89%) had MA-% between 0.1 and 2.0% 

(Fig. 16). Additional studies reporting MA-% in longnose 

sucker were not found. Largescale sucker from the CRB had 

a basinwide mean MA-% of 2.4% with station means ranging 

from 1.8 to 3.8% (Hinck and others, 2004), which is greater 

than longnose sucker data from the YRB.

MA-% data for burbot were only available for Station 

305 (Table 19). The station mean was 4.7% with a range of 

0.02-15.13%, which is greater than the MA-% for northern 

pike and longnose sucker. Other studies documenting MA-# 

in burbot were not available.
Results and Discussion 51

CF

%

SSI

1.2

1.0

0.8

0.6

0.4

0.2

0.0

0.5

0.4

0.3

0.2

0.1

0.0

301 302 303 304 305 306 307 308 309 310

Station

Figure 14. Fish health indicators by station in female and male 

longnose sucker collected in the Yukon River Basin in 2002. 

Indicators include condition factor (CF) and splenosomatic index 

(SSI). Shown for each group are points representing individual 

fish and the mean (red horizontal line), median (black horizontal 

line), interquartile range (box), and the 10th and 90th percentiles 

(whiskers). Stations are ordered upstream to downstream. See 

Table 1 for station descriptions.

Fish Health Indicators: Summary

Fish health indicators for this project and previous BEST 

projects were selected to evaluate major organ systems and 

their functions (Hinck and others, 2004; Schmitt, 2002a; 

Schmitt and others, 2004). The BEST LRMN continued to 

accumulate information on the target species for comparison 

with various large river basins and regions throughout the 

U.S. and for the determination of “normal” ranges for many 

of these indicators. Various factors including age, gender, reproductive status, and geographic location as well as 

contaminants can affect these fish health indicators that were 

selected to reflect overall organismal health of the fish and 

their populations.

Fish were collected in the summer and fall of 2002, sexed 

and aged, and analyzed by species in an attempt to eliminate 

as many confounding factors as possible. Potential effects of 

gender and age on comparisons among stations were evaluated 

statistically. Age, known to significantly influence MA-# in 

some fishes, was considered in the statistical model for station 

comparisons of these parameters (Brown and George, 1985). 

Analysis of the data indicated no effect of gender or age (for 

the MA parameters) on external lesions, CF, HAI, MA-#, 

MA-size, or MA-% in northern pike or longnose sucker, SSI 

in longnose sucker, and HSI in northern pike. SSI in northern 

pike differed significantly between genders; therefore, males 

and females were evaluated separately. HSI in northern pike 

was analyzed by gender due to the role of the liver in vitellogenesis and the associated physiological changes in the liver 

throughout the female reproductive cycle.

Forty-seven percent of the fish collected from the YRB 

were identified as having external lesions. External lesions 

were identified on 51% of northern pike, 41% of longnose 

sucker, and 8% of burbot. Fish from several stations had high 

proportions (>60%) of external lesions. However, most of 

the lesions were attributed to old scars or marks on the body 

surface. No fish were identified as having active fin erosion, 

skeletal or fin deformities, body surface tumors, or eye lesions 

that have been previously associated with exposure to anthropogenic stressors or degraded environments (Fournie and others, 1996; McCain and others, 1992; Sindermann, 1979).

Caution must be exercised when comparing external 

lesions of YRB fish with those of other studies and even in 

comparing stations in our study. Errors in proportions of 

anomalous fish can result from biased or differential examination of fish, species composition, habitat, and other factors 

unrelated to environmental degradation (Leonard and Orth, 

1986). This error in our study could be compounded because 

many different individuals were involved in assessing external 

lesions. A second confounding factor in comparing the results 

of various studies is the consideration of different anomalies. 

This study evaluated abnormalities of the body surface, eyes, 

opercles, and fins, including deformities and parasites.

The HAI, which is also an assessment of grossly visible 

lesions, is more comprehensive than the incidence of external lesions because it accounts for both external and internal 

abnormalities. To our knowledge, this methodology has had 

limited use with northern pike and longnose sucker. Station 

means of HAI in the YRB ranged from 10 to 92 for northern 

pike and 29 to 70 for longnose sucker. Northern pike from 

the MRB (Schmitt and others, 2002a) and RGB (Schmitt and 

others, 2004) had similar HAI scores. No other studies were 

found that evaluated HAI in northern pike. Studies examining HAI in longnose sucker were limited but HAI in YRB fish 

were generally less than sucker (Catostomus spp.) from the 

CRB (Hinck and others, 2004).

CF may indicate changes at the organism level and is 

directly affected by nutrition (Tyler and Dunn, 1976), as well 

as by season, sexual maturation, and disease (Adams and others, 1982; Denton and Yousef, 1976; Möller, 1985). Elevated 

CF has been linked to exposure to contaminants such as pulp 

mill effluent (Adams and others, 1992; McMaster and others, 

1991; Oakes and others, 2004) and municipal sewage effluents 
5

2

Table 19. Arithmetic mean of macrophage aggregate (MA) by species, gender, and station in northern pike, longnose sucker, and burbot collected in the Yukon River 

Basin in 2002. Number of samples (n ), minimum (min.), maximum (max.), and standard error (SE) are also given. Stations are ordered upstream to downstream. The maximum station mean for each taxon is shown in bold.

MA-# (MA/mm2) MA-size (μm2) MA-% (%

Min.

) Species and Station 

n Mean Min. Max. SE Mean Min. Max. SE Mean Max. SE 

Northern pike

Basin Total 155 3.7 0.0 12.9 0.18 1134 0 4434 47 0.43 0.00 1.78 0.03 Charley-Kandik, AK (301) 6 3.2 1.2 5.3 0.65 1270 804 2304 226 0.38 0.19 0.71 0.07 Fish Hook Bend, AK (302) 20 3.3 0.0 10.0 0.60 1245 0 2530 137 0.47 0.00 1.29 0.09 Fort Yukon, AK (303) 22 4.0 0.6 11.2 0.53 849 398 1729 69 0.34 0.04 0.95 0.05 The Bridge, AK (304) 9 3.5 1.8 6.5 0.51 1155 215 1847 212 0.45 0.04 1.06 0.11 Fairbanks, AK (305) 3 3.7 1.8 5.9 1.19 1225 688 1933 369 0.54 0.19 1.17 0.32 Tolovana, AK (306) 20 5.2 1.2 12.9 0.68 1087 343 2756 127 0.59 0.11 1.78 0.11 Tanana, AK (307) 18 3.0 0.6 6.5 0.37 1333 727 2348 114 0.43 0.08 1.09 0.08 Galena, AK (308) 20 2.7 0.6 7.1 0.39 1276 231 2886 132 0.35 0.01 1.10 0.06 Innoko, AK (309) 20 4.6 1.8 8.2 0.41 994 402 1897 81 0.47 0.12 0.92 0.05 Kotlik, AK (310) 17 3.0 0.6 7.6 0.47 1138 0 4434 232 0.31 0.00 1.17 0.07 

Longnose sucker

Basin Total 46 5.5 0.0 21.2 0.64 2095 0 8201 253 1.26 0.00 4.96 0.18 Charley-Kandik, AK (301) 12 6.9 1.2 15.3 1.18 2672 1196 4258 299 1.78 0.16 2.96 0.25 

The Bridge, AK (304) 2 11.5 1.8 21.2 9.70 1613 743 2482 870 1.04 0.45 1.62 0.59 Fairbanks, AK (305) 21 5.3 0.0 20.0 1.06 2085 0 8201 470 1.20 0.00 4.96 0.31 Tolovana, AK (306) 3 5.9 0.6 10.0 2.78 1808 1417 2005 196 1.07 0.12 2.06 0.56 Galena, AK (308) 8 2.4 0.0 9.4 1.16 1486 0 4091 572 0.78 0.00 3.24 0.42 

Burbot

Fairbanks, AK (305) 12 3.9 0.6 8.8 0.64 62860 368 250000 22434 4.74 0.02 15.13 1.38 

EnvironmentalContaminantsandtheirEffectsonFish
4

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Results and Discussion 53

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MA-# 25

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301 302 303 304 305 306 307 308 309 310

Station

Figure 15. Splenic macrophage aggregate parameters by station in northern pike collected in the Yukon River Basin in 2002. 

Parameters include macrophage aggregate density (MA-#), macrophage aggregate area (MA-size), and percent of splenic tissue 

occupied by macrophage aggregates (MA-%). Shown for each 

group are points representing individual fish and the mean (red 

horizontal line), median (black horizontal line), interquartile range 

(box), and the 10th and 90th percentiles (whiskers). Stations are 

ordered upstream to downstream. See Table 1 for station descriptions.

0

301 302 303 304 305 306 307 308 309 310

Station

Figure 16. Splenic macrophage aggregate parameters by station 

in longnose sucker collected in the Yukon River Basin in 2002. 

Parameters include macrophage aggregate density (MA-#), macrophage aggregate area (MA-size), and percent of splenic tissue 

occupied by macrophage aggregates (MA-%). Shown for each 

group are points representing individual fish and the mean (red 

horizontal line), median (black horizontal line), interquartile range 

(box), and the 10th and 90th percentiles (whiskers). Stations are 

ordered upstream to downstream. See Table 1 for station descriptions.
54 Environmental Contaminants and their Effects on Fish

(Oakes and others, 2004), whereas diminished CF has been 

observed after exposure to contaminants such as metals and 

petroleum (Kiceniuk and Khan, 1987; Miller and others, 1992; 

Munkittrick and Dixon, 1988). Condition factor can also vary 

among locations within a species (Doyon and others, 1988; 

Fisher and others, 1996). The range of CF station means for 

northern pike in the YRB was 0.51-0.67 with no station being 

notable for low CF. Longnose sucker had greater CF than 

northern pike with station means ranging from 0.76 to 0.94 

with no significant differences among stations.

The HSI may vary with season (Beamish and others, 

1996; Delahunty and de Vlaming, 1980), temperature (Fine 

and others, 1996), and nutrition (Daniels and Robinson, 1986; 

Foster and others, 1993) as well as with gender and changes 

in gonadal status (Fabacher and Baumann, 1985; Förlin and 

Haux, 1990; Grady and others, 1992). It is also the organosomatic index for which changes are most often associated with 

contaminant exposure (Adams and McLean, 1985). Increased 

HSI has been reported with exposure of wild fish to organic 

contaminants, most often PAHs and PCBs, whereas laboratory exposures of fish to metals, crude oil, certain pesticides, 

and bleached kraft mill effluent have resulted in HSI decreases 

(Schmitt and Dethloff, 2000). A comparative range for normal 

liver weight in fish is 1-3% of body weight, with relative 

weights >2% being uncommon (Gingerich, 1982). HSI were 

not calculated for longnose sucker due to the diffuse nature 

of their livers. Only northern pike from Station 310 had HSI 

>3%. However, these fish were collected in early May, resulting in elevated, but not significantly greater, HSI compared 

to the other YRB stations where northern pike were collected 

after spawning had occurred.

The SSI is measured to determine changes in the relative size of the spleen, a primary hematopoietic organ in fish. 

The SSI can differ among species, genders, and locations and 

can change over age, size, gonadal development, and season 

(Krykhtin, 1976; Ruklov, 1979; White and Fletcher, 1985). 

Studies have also documented changes in relative spleen size 

with exposure to chemical contaminants. Fish exposed to 

organic contaminants alone or in combination with metals 

have had decreased SSI, but increased SSI has rarely been 

documented with contaminant exposure (Schmitt and Dethloff, 

2000). An increase in SSI is considered indicative of disease 

or immune problems (Goede and Barton, 1990). Capture and 

holding stress have been reported to alter SSI and HSI in field 

studies (Schmitt and Dethloff, 2000). Stations in the YRB are 

described as having high or low SSI relative to other stations 

because “normal” ranges are not available for northern pike 

and longnose sucker. Station means for SSI ranged from 0.09 

to 0.15% in female northern pike and 0.10 to 0.18% in male 

northern pike. Stations 306, 308, and 310 had the greatest station means (>0.12%) for female northern pike with SSI values 

in individual fish exceeding 0.15%. SSI in longnose sucker 

was greater than in northern pike. Longnose sucker from 

Stations 301 and 305 had greater mean SSI although other stations had limited sample sizes.

Macrophage aggregate parameters were also evaluated 

in the YRB. Station means for MA-# were 2.7-5.2 MA/mm2

in northern pike and 2.4-11.5 MA/mm2 in longnose sucker. 

Fournie and others (2001) suggested than splenic MA densities of >40 MA/mm2 in at least one fish from a site were 

correlated with hypoxic stress or high levels of sediment 

contamination for a variety of estuarine fishes and irrespective 

of age. There is insufficient data to know if this is a reasonable reference number for freshwater fishes or how MA may 

be correlated with body burdens of various contaminants. 

However, none of the fish collected from the YRB exceeded 

40 MA/mm2.

Increases in MA parameters in fish collected from 

specific contaminated sites relative to reference groups or 

sites have been found in both laboratory and field studies 

(Blazer and others, 1994; 1997; Wolke, 1992). Programs such 

as the USEPA Environmental Monitoring and Assessment 

Program (EMAP) Estuaries program (Fournie and others, 

2001; Summers and others, 1993) and NOAA’s Status and 

Trends programs (Chang and others, 1998) have also used MA 

parameters as bioindicators. Macrophage aggregates have 

been identified in various tissues including spleen, liver, and 

kidney although most studies using splenic MAs have been 

performed in marine or estuarine environments. Most studies 

have only evaluated MA density, and even for this parameter, 

no regional baseline information exists to establish a “normal” 

value for any species. To our knowledge, there have not been 

any studies evaluating MAs and potential effects of contaminant exposure in northern pike or longnose sucker. Numerous 

studies have reported various factors including size, nutritional 

status (Agius, 1979; 1980; Agius and Roberts, 1981; Wolke 

and others, 1985), age (Blazer and others, 1987; Brown and 

George, 1985; Couillard and Hodson, 1996), and exposure 

time (many as reported in Schmitt and Dethloff, 2000) can 

affect macrophage aggregates in different species.

Histological evaluation of various tissues suggested the 

majority of lesions observed were parasite related (Appendix 

2). Five percent of the northern pike at Station 309 (Innoko 

NWR Field Station) had altered foci in the liver, and 33% 

of longnose sucker at Station 306 (Tolovana) had bile duct 

proliferation (Appendix 2). Both of these lesions have been 

associated with exposure to contaminants in other fish species 

(Bunton and others, 1987; Myers and others, 1994; Stehr and 

others, 2003; Teh and Hinton, 1993). 

Reproductive Biomarkers

Gonadal Histopatholgy, Vitellogenin, and Steroid

Hormones

Gonadal histopathology and GSI are reproductive indicators that provide structural information about gonadal health 

and maturational stage (Schmitt and Dethloff, 2000). Vitel-
55

logenin provides information on stage of maturation and the 

estrogenicity of various compounds (Schmitt and Dethloff, 

2000). Steroid hormones including estradiol (E2), 11-ketotestosterone (KT), and estradiol/11-ketotestosterone ratio (E/KT) 

are used to monitor subtle physiological changes that could 

lead to long-term population level effects (Schmitt and Dethloff, 2000). Evaluation of all of these reproductive biomarkers 

may be confounded by factors including season, age, gender, 

and chemical contaminants that have been reported to affect 

these reproductive biomarkers (Schmitt and Dethloff, 2000). 

Reproductive biomarkers were evaluated relative to the stage 

of gonad development of fish in the YRB (see Figs. 2 and 3). 

The gender and gonadal stage of northern pike and longnose sucker did not influence GSI, vtg, or atresia, but steroid 

hormones were influenced by stage or gender in some models 

(Table 13). The data for male and female northern pike and 

longnose sucker were examined separately based on a review 

of the literature and previous BEST LRMN projects. Steroid 

hormone data for Station 307 was limited to a single male 

northern pike.

Female Northern Pike

Examining the stage of gonad development is critical 

for the interpretation of reproductive biomarkers. Female 

northern pike were in stages 1-5 with the majority identified as 

stage 2 (33%) and stage 5 (32%) (Fig. 17). Other stages presented were stage 1 (20%), stage 3 (1%), and stage 4 (14%). 

Stage-1 females were collected from Stations 303, 304, 305, 

306, 307, and 309; stage-2 females were identified at Stations 302, 303, 304, 305, 306, 308, and 309. A single stage-3 

female northern pike was collected at Station 303. Female 

northern pike from Station 310 were all stage 4, and other stations having stage-4 females included Stations 305, 306, and 

307. Stations 301, 303, 304, 306, 307, and 308 had stage-5 

female northern pike. 

The basinwide mean GSI was 2.0% in female northern 

pike in the YRB (Table 20). The GSI was greatest (11.9%) 

in females from Station 310, with individual fish having GSI 

ranging from 5.7 to 16.5%. Other station means were <2.8% 

for female northern pike (Table 20; Fig. 18). However, fish 

from Station 310 were collected earlier (in early May) than 

other stations. All female pike from Station 310 were stage 4 

(late development of oocytes with large follicles). In fact, all 

female northern pike with GSI >2% were stage 4. All other 

female northern pike had GSI ranging between 1 and 2% (Fig. 

18). However, GSI in female northern pike did not vary significantly among YRB stations, and stage was not a significant 

factor in the model (Table 13). Few studies were located that 

described GSI in female northern pike. GSI ranged from 0.05 

to 2.6% in female northern pike collected in September from 

the Missouri River near Garrison Dam, North Dakota; gonadal 

stage of northern pike was not determined in this study 

(McDonald and others, 2002). Schmitt and others (2004) 

reported GSI in male northern pike collected in SeptemberResults and Discussion

October to range from 0.5 to 4.9% near Alomosa, Colorado in 

the RGB, although no stage data were available for these fish.

Female and male northern pike were examined separately for vtg even though gender was not found to influence 

vtg concentrations (Table 13). This lack of gender difference 

in concentrations of vtg may be a result of small sample size 

and narrow range of concentrations or both. The basinwide 

mean for vtg in female northern pike was 0.77 mg/mL, and the 

station means ranged from 0.09 mg/mL at Station 308 to 5.32 

mg/mL at Station 305 (Table 20). However, vtg data from 

Station 305 was limited to one stage-4 female northern pike 

collected in October whereas most other northern pike were 

collected during the summer (June-July). This indicated that 

gonadal stage and, to some extent, collection date influenced 

concentrations of vtg. Stage-4 female northern pike from 

Stations 301 and 310 also had greater vtg concentrations than 

other YRB stations. Most female northern pike (67%) had 

concentrations of vtg between 0.1 and 1.3 mg/mL (Fig. 18). 

Other studies reporting concentrations of vtg in female northern pike were not found.

Mean percent atresia in northern pike was similar among 

YRB stations. Basinwide mean percent atresia was 1.1%, and 

station means ranged from 0.0% at Station 310 to 2.9% at Station 304 (Table 20). Percent atresia was <8% for all northern 

pike except in four females from Stations 302 and 304 (Fig. 

18). YRB station means did not significantly differ for percent 

atresia in female northern pike (Table 13). Atresia data is 

limited for northern pike. June (1970) concluded that high 

incidence of atresia (>10%) in northern pike ovaries from Missouri River impoundments was associated with fluctuations in 

water temperature or level. In addition, follicular atresia was 

found to be more common in northern pike than others species 

including burbot in a Missouri River reservoir (June, 1977).

Female and male northern pike were examined separately 

for steroid hormones because gender influenced concentrations of KT (Table 13). The basinwide mean of E2 in female 

northern pike was 1,111 pg/mL, and station means ranged 

from 393 pg/mL at Station 309 to 1,565 pg/mL at Station 

302 (Table 21). Gonadal stage and collection date did not 

appear to influence concentrations of E2 in female northern 

pike, and station means did not differ significantly in regards 

to E2 (Table 13). Concentrations of E2 were >2,000 pg/mL 

in female northern pike from Stations 302 and 308 (Fig. 18). 

Most female northern pike (78%) had concentrations of E2 

between 290 and 2,000 pg/mL (Fig. 18).

Concentrations of KT were less than E2 in female northern pike. The basinwide mean of KT in female northern pike 

was 494 pg/mL (Table 21). Station means for KT in female 

northern pike varied significantly and ranged from 162 pg/mL 

at Station 305 to 708 pg/mL at Station 304 (Fig. 18; Table 13). 

Female northern pike from Stations 303, 304, 306, 308, and 

309 had concentrations of KT >1,000 pg/mL. Mean station 

E/KT ratios ranged from 1.63 at Station 309 to 6.83 at Station 

302 in female northern pike (Table 21; Fig. 18). Female northern pike (26%) from all stations except Stations 301, 305, and 

307, had E/KT ratios <1.0; gondal stage of these fish varied 
56 Environmental Contaminants and their Effects on Fish % 

M F 

2 4 

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301 302 303 304 305 306 307 308 309 310 Basin 

M F

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29 

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12 

28 

6/5/02-6/6/02 8/14/02-8/16/02 6/12/02-6/14/02 6/4/02-6/7/02 5/30/02-5/31/02, 

6/28/02,10/10/02 

6/4/02-6/6/02 6/5/02-6/7/02 6/10/02-6/14/02 7/15/02-7/17/02 5/9/02-5/12/02 

100

90

80

70

60

50

40

30

20

10

0

Stage 5 

Stage 4 

Stage 3 

Stage 2 

Stage 1 

Stage 0 

Station 

Figure 17. Gonadal stage of female and male northern pike collected in the Yukon River Basin in 2002. Shown are the percentages 

(y-axis) and sample sizes (within the bars) of fish in each stage. The collection dates for each station are also shown. Stations are 

ordered upstream to downstream. See Table 1 for station descriptions.

(Fig. 18). Other studies reporting concentrations of steroid 

hormones in female northern pike were not found.

Male Northern Pike

Stage of gonad development and gender were examined 

in order to interpret reproductive biomarkers in male northern 

pike. Stage of male northern pike was not related to capture 

date. Male northern pike were in stages 0-4, with the majority 

identified as stage 1 (34%) and stage 4 (34%) (Fig. 17). Other 

stages present were stage 0 (3%), stage 2 (12%), and stage 

3 (18%). Stage-0 males were collected from Station 303. 

Stage-1 males were collected from Stations 303, 306, 308, and 

309. All male northern pike from Station 302 were stage 2, 

and stage-2 males were collected from Stations 308 and 309. 

Stage-3 male northern pike were collected at Stations 304, 

306, 307, and 310, and stage-4 males were collected from all 

stations except Station 302. 

Basinwide mean GSI in male northern pike (0.5%) was 

less than in female northern pike (2.0%). GSI in male northern pike ranged from 0.3% at Stations 303 and 308 to 1.5% at 

Station 302 (Table 20). Stations 302 and 310 consistently had 

fish with GSI >1.0%, but these fish did not have GSI significantly greater than other stations (Fig. 19; Table 13). All male 

northern pike from Station 302 were stage 2 (mid-spermatogenic which includes spermatocytes, spermatids, and spermatozoa). Male northern pike from Station 310 with GSI >1.0% 

were stage 3 (late spermatogenic in which mature sperm are 

predominant). Previous studies reporting GSI in male northern pike are limited. GSI ranged from 0.21 to 1.4% in male 

northern pike collected in September from the Missouri River 

near Garrison Dam, North Dakota (McDonald and others, 

2002). Schmitt and others (2004) reported GSI of 0.2-4.2% in 

male northern pike collected in September-October from Alomosa, Colorado in the RGB. Gonadal stage of fish from these 

studies was not reported (McDonald and others, 2002; Schmitt 

and others, 2004).

Concentrations of vtg were measured in male northern 

pike; and many (50%) were <LOD (0.001 mg/mL). The 

basinwide mean of vtg in male northern pike was 0.014 mg/

mL, and station means ranged from <0.001 mg/mL at Station 307 to 0.097 mg/mL at Station 301 (Table 20; Fig. 19). 

Concentrations of vtg in northern pike >LOD (0.001 mg/mL) 

were measured in fish at all stations except Stations 304, 305 
5

7

Table 20. Arithmetic mean of gonadosomatic index (GSI), vitellogenin (vtg), and atresia by gender, species, and station in northern pike, longnose sucker, and burbot collected in the Yukon River Basin in 2002. Number of samples (n ), minimum (min.), maximum (max.), and standard error (SE) are also given. Censored 

values were represented by one half the LOD in the computation of means. The percent males that had concentrations of vtg >0.01 mg/mL are also presented.Stations are ordered upstream to downstream. The maximum station mean for each species is shown in bold.

Gender, Species, and Station GSnI (%) Vtng (mg%/mL) Atnresia (%) Mean Min. Max. SE Mean Min. Max. SE Mean Min. Max. SE 

Female

Northern pike

Basin Total 88 2.0 0.2 16.5 0.39 73 -- 0.77 0.001 5.32 0.11 88 1.1 0 10 0.2 Charley-Kandik, AK (301) 4 1.0 0.6 1.7 0.2 4 -- 1.41 0.001 2.78 0.76 4 0.3 0 1 0.3 Fish Hook Bend, AK (302) 15 0.9 0.4 1.4 0.1 15 -- 0.73 0.013 1.65 0.13 15 2.5 0 10 0.8 Fort Yukon, AK (303) 11 0.5 0.3 0.7 0.0 11 -- 0.22 0.001 0.85 0.09 11 0.1 0 1 0.1 The Bridge, AK (304) 7 0.6 0.3 0.9 0.1 7 -- 0.52 0.001 1.10 0.15 7 2.9 0 9 1.5 Fairbanks, AK (305) 3 2.8 1.1 6.2 1.7 1 -- 5.32 -- -- -- 3 1.0 0 3 1.0 Tolovana, AK (306) 10 1.3 0.3 8.8 0.8 9 -- 0.38 0.001 1.24 0.16 10 0.8 0 4 0.5 Tanana, AK (307) 12 0.7 0.2 3.7 0.3 -- -- -- -- -- -- 12 0.8 0 4 0.4 Galena, AK (308) 8 0.5 0.3 0.6 0.0 8 -- 0.20 0.001 0.69 0.08 8 0.6 0 3 0.4 Innoko, AK (309) 9 0.7 0.4 0.9 0.1 9 -- 0.09 0.001 0.39 0.05 9 1.1 0 4 0.5 Kotlik, AK (310) 9 11.9 5.7 16.5 1.1 9 -- 1.72 0.553 3.63 0.29 9 0.0 0 0 0.0 

Longnose sucker

Basin Total 31 3.0 0.6 14.1 0.6 30 -- 3.86 0.009 10.74 0.61 31 0.0 0 3 0.1 Charley-Kandik, AK (301) 11 2.0 1.3 2.9 0.1 11 -- 4.83 0.385 10.57 1.09 11 0.5 0 3 0.3 

The Bridge, AK (304) 2 1.5 1.1 2.0 0.5 2 -- 2.63 0.048 5.21 2.58 2 0.0 0 0 0.0 Fairbanks, AK (305) 9 6.4 0.9 14.1 1.6 8 -- 4.18 0.030 8.65 0.88 9 0.0 0 0 0.0 Tolovana, AK (306) 2 1.0 0.6 1.5 0.5 2 -- 0.03 0.015 0.05 0.02 2 0.5 0 1 0.5 Galena, AK (308) 7 1.2 0.6 1.8 0.2 7 -- 3.44 0.009 10.74 1.44 7 0.1 0 1 0.1 

Burbot

Fairbanks, AK (305) 8 3.0 0.5 5.0 0.7 -- -- -- -- -- -- 8 4.6 0 29 3.2 

Male

Northern pike

Basin Total 68 0.5 0.1 1.8 0.1 62 27 0.014 0.001 0.194 0.001 -- -- -- -- --Charley-Kandik, AK (301) 2 0.6 0.5 0.8 0.2 2 50 0.097 0.001 0.194 0.097 -- -- -- -- --

Fish Hook Bend, AK (302) 4 1.5 1.1 1.8 0.1 5 25 0.009 0.001 0.041 0.008 -- -- -- -- --

Fort Yukon, AK (303) 11 0.3 0.2 0.5 0.0 11 9 0.005 0.001 0.017 0.002 -- -- -- -- --The Bridge, AK (304) 2 0.5 0.4 0.5 0.1 2 0 0.001 0.001 0.001 -- -- -- -- -- --Tolovana, AK (306) 10 0.4 0.1 1.1 0.1 10 10 0.003 0.001 0.021 0.002 -- -- -- -- --Tanana, AK (307) 8 0.6 0.2 1.1 0.1 1 0 0.001 -- -- -- -- -- -- -- --Galena, AK (308) 12 0.3 0.2 0.3 0.0 12 50 0.031 0.001 0.181 0.016 -- -- -- -- --Innoko, AK (309) 11 0.4 0.2 0.9 0.1 11 55 0.009 0.001 0.019 0.002 -- -- -- -- --Kotlik, AK (310) 8 1.3 0.2 1.7 0.2 8 13 0.008 0.001 0.035 0.004 -- -- -- -- --

Longnose sucker

Basin Total 14 1.7 0.4 3.7 0.6 14 64 0.018 0.001 0.043 0.004 -- -- -- -- --Charley-Kandik, AK (301) 1 1.5 -- -- -- 1 0 0.003 -- -- -- -- -- -- -- --Fairbanks, AK (305) 11 1.9 0.4 3.7 0.3 11 73 0.020 0.001 0.043 0.004 -- -- -- -- --Tolovana, AK (306) 1 0.4 0.4 0.4 -- 1 0 0.007 -- -- -- -- -- -- -- --Galena, AK (308) 1 0.4 0.4 0.4 -- 1 100 0.020 -- -- -- -- -- -- -- --

Burbot

Basin Total 5 0.3 0.1 0.7 0.1 -- -- -- -- -- -- -- -- -- -- --Fairbanks, AK (305) 4 0.3 0.1 0.7 0.1 -- -- -- -- -- -- -- -- -- -- --Kotlik, AK (310) 1 0.1 -- -- -- -- -- -- -- -- -- -- -- -- -- --

ResultsandDiscussion
58 Environmental Contaminants and their Effects on Fish

18

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1500

1000

500

0

2500

2000

1500

1000

500

0

16

14

12

10

8

6

4

2

0

GSI

vtg

atresia

E2

KT

E/KT

301 302 303 304 305 306 307 308 309 310

Station

Figure 18. Reproductive health indicators by station in female 

northern pike collected in the Yukon River Basin in 2002. Indicators include gonadosomatic index (GSI), vitellogenin (vtg), atresia, 

estradiol (E2), 11-ketotestosterone (KT), and E/KT ratio. Shown 

for each group are points representing individual fish and the 

mean (red horizontal line), median (black horizontal line), interquartile range (box), and the 10th and 90th percentiles (whiskers). 

Stations are ordered upstream to downstream. See Table 1 for 

station descriptions. 

pg/mL pg/mL %

mg/mL %

(no male northern pike collected), and 307. Individual male 

northern pike from all stations except Stations 304 and 307 

had concentrations of vtg >0.01 mg/mL (Table 20). Multiple 

male northern pike from Stations 308 and 309 had concentrations of vtg >0.01 mg/mL, and Stations 301 and 308 had male 

northern pike with concentrations of vtg >0.10 mg/mL (Fig. 

19). Concentrations of vtg >0.01 mg/mL indicate an estrogenic response in these male fish.

The basinwide mean concentration of KT in male 

northern pike was 933 pg/mL, and the station means ranged 

from 408 pg/mL at Station 309 to 1,209 pg/mL at Station 

302 (Table 21). Stations 309 and 302 also had the lowest and 

greatest concentrations of E2 in female northern pike, respectively. Station, stage, and gonadal stage influenced concentrations of KT in northern pike (Table 13). Male northern pike 

from Stations 306, 307, and 309 consistently had concentrations of KT <750 pg/mL and did not exceed 1,000 pg/mL (Fig. 

19).

Concentrations of E2 were less than those of KT in most 

male northern pike. The basinwide mean concentration of 

E2 was 531 pg/mL in male northern pike (Table 21). Station 

means for E2 in male northern pike ranged from 139 pg/mL 

at Station 301 to 2,091 pg/mL at Station 307 (n=1) (Table 

21). All other station means were <936 pg/mL and did not 

differ significantly in concentrations of E2 (Fig. 19; Table 

13). Stations 304, 306, 307, 308, and 310 had male northern 

pike with concentrations of E2 >1,000 pg/mL. E/KT ratios in 

male northern pike ranged from 0.11 at Station 301 to 4.07 at 

Station 304 (Table 21; Fig. 19). Twenty-one percent of male 

northern pike, including individual fish from Stations 302, 

304, 306, 308, 309, and 310, had E/KT ratios >1.0 and were 

in various stages of gonadal development (Fig. 19). Other 

studies evaluating steroid hormones concentrations in male 

northern pike were not found.

Gender of one northern pike from Station 309 was unable 

to be determined. This fish had a GSI of 0.3% and concentration of vtg of 0.007 mg/mL. Concentrations of steroid 

hormones for this fish were 105 pg/mL for E2, 215 pg/mL for 

KT, and the E/KT ratio was 0.49.

Female Longnose Sucker

Reproductive biomarker data were limited to five stations 

for longnose sucker (Fig. 20). Female longnose sucker were 

in stages 1 (3%), 2 (61%), 3 (20%), and 5 (16%). Stage was 

not correlated with capture date. Stage-2 females were present 

at all five stations, and stage-3 female longnose sucker were 

collected at Stations 305 and 308. Stage-1 female longnose 

sucker were found at Station 306, and stage-5 females were 

identified at Stations 301 and 305. 

Female longnose sucker had a basinwide mean of 3.0% 

for GSI, and station means ranged from 1.0% at Station 306 to 

6.4% at Station 305 in the YRB (Table 20). Female longnose 

sucker from Station 305 consistently had GSI greater than 

other stations (Fig. 21; Table 13). However, all fish from 
Results and Discussion 59

Table 21. Arithmetic mean of estradiol (E2), ll-ketotestosterone (KT), and ratio of E/KT by gender, species, and station in northern pike, longnose 

sucker, and burobt collected in the Yukon River Basin in 2002. Number of samples ( n ), minimum (min.), maximum (max.), and standard error (SE) are 

also given. Stations are ordered upstream to downstream. The maximum station mean for each taxon is shown in bold. Only individual fish with 

histologically determined gender were included in this table. 

Gender, Species, and Station Min. Max. SE Min. Max. SE Mean Min. Max. SE

E2 (pg/mL) E/KT

n Mean 

KT (pg/mL) 

Mean 

Female 

Northern pike 

Basin Total 72 1111 145 2852 82 494 51 2121 46 3.53 0.15 13.95 0.37 

Charley-Kandik, AK (301) 4 991 717 1297 130 398 247 573 74 2.74 1.47 4.20 0.57 

Fish Hook Bend, AK (302) 15 1565 145 2852 244 270 89 503 30 6.83 0.59 13.95 1.20 

Fort Yukon, AK (303) 11 1117 461 1756 134 679 376 1449 106 2.13 0.43 4.30 0.39 

The Bridge, AK (304) 7 1126 389 1664 201 708 262 1741 224 2.98 0.22 5.91 0.81 

Fairbanks, AK (305) 1 493 -- -- -- 162 -- -- -- 3.04 -- -- --

Tolovana, AK (306) 9 1005 216 1532 169 540 158 1471 130 2.64 0.15 5.72 0.59 

Tanana, AK (307) 0 -- -- -- -- -- -- -- -- -- -- -- --

Galena, AK (308) 8 1057 211 2292 304 444 148 1049 116 3.16 0.57 7.31 0.91 

Innoko, AK (309) 9 393 160 832 75 397 51 705 74 1.63 0.26 5.12 0.55 

Kotlik, AK (310) 8 1355 384 1884 168 670 197 2121 227 3.67 0.18 7.58 0.83 

Longnose sucker 

Basin Total 31 1402 467 2748 106 361 118 782 31 5.27 0.73 18.53 0.77 

Charley-Kandik, AK (301) 11 1126 513 1786 137 379 163 585 42 3.49 0.88 9.07 0.66 

The Bridge, AK (304) 2 1214 1106 1321 108 298 178 417 120 4.69 3.17 6.21 1.52 

Fairbanks, AK (305) 9 1630 834 2748 190 363 118 644 58 5.96 1.30 18.53 1.65 

Tolovana, AK (306) 2 1332 467 2197 865 440 241 638 199 4.92 0.73 9.12 4.19 

Galena, AK (308) 7 1618 882 2725 249 327 126 782 85 7.46 1.13 17.47 2.11 

Burbot 

Fairbanks, AK (305) 8 534 115 1720 215 303 145 776 81 1.46 0.66 2.38 0.22 

Male 

Northern pike 

Basin Total 61 531 102 2588 62 933 91 2149 71 1.32 0.07 28.44 0.48 

Charley-Kandik, AK (301) 2 139 102 175 37 1209 1171 1246 38 0.11 0.09 0.14 0.03 

Fish Hook Bend, AK (302) 5 305 135 513 82 1127 191 1886 345 0.53 0.07 1.04 0.22 

Fort Yukon, AK (303) 11 448 115 835 67 1208 717 1677 100 0.36 0.10 0.50 0.04 

The Bridge, AK (304) 2 936 775 1096 161 877 143 1610 734 4.07 0.48 7.66 3.59 

Tolovana, AK (306) 9 489 134 1957 202 603 342 911 69 0.99 0.19 3.45 0.40 

Tanana, AK (307) 1 2091 -- -- -- 548 -- -- -- 3.82 -- -- --

Galena, AK (308) 12 796 170 2588 188 1206 91 2149 215 3.07 0.08 28.44 2.32 

Innoko, AK (309) 11 355 102 894 85 408 184 703 60 1.11 0.17 4.86 0.39 

Kotlik, AK (310) 8 478 239 1039 90 1108 765 1573 93 0.48 0.25 1.29 0.13 

Longnose sucker 

Basin Total 14 632 152 2515 212 755 131 1518 148 1.51 0.11 7.17 0.56 

Eagle, AK (301) 1 246 -- -- -- 642 -- -- -- 0.38 -- -- --

Fairbanks, AK (305) 11 533 152 2515 201 848 178 1518 176 1.22 0.11 7.17 0.61 

Nenana, AK (306) 1 2459 -- -- -- 468 -- -- -- 5.25 -- -- --

Galena, AK (308) 1 278 -- -- -- 131 -- -- -- 2.12 -- -- --

Burbot 

Basin Total 5 646 105 1390 214 1082 235 1686 245 1.49 0.08 5.91 1.11 

Fairbanks, AK (305) 4 658 105 1390 276 932 235 1356 249 1.78 0.08 5.91 1.39 

Kotlik, AK (310) 1 596 -- -- -- 1686 -- -- -- 0.35 -- -- --

Station 305 with GSI >8.0% were stage 3 (late vitellogenic ton, Montana (0.0-63.6 mg/mL) and Grand Coulee, Washingfollicles), a gonadal stage in which high GSI values are typi- ton (4.1 mg/mL) in the upper CRB (Hinck and others, 2004) 

cal. Longnose sucker from the CRB had GSI ranging from were greater than concentrations in YRB longnose sucker. 

0.6 to 12.4% but gonadal stage was not determined (Hinck and Concentrations of vtg in female largescale sucker from the 

others, 2004). CRB had a basinwide mean of 38.8 mg/mL, and station means 

Female and male longnose sucker were examined sepa- ranged from 14.1 mg/mL near Grand Coulee, Washington to 

rately for vtg although gender did not influence vtg concentra- 66.5 mg/mL near Oregon City, Oregon (Hinck and others, 

tions in the YRB (Table 13). The basinwide mean of vtg in 2004). Other studies reporting concentrations of plasma vtg in 

female longnose sucker was 3.86 mg/mL, and station means female longnose sucker were not found.

ranged from 0.03 mg/mL at Station 306 to 4.83 mg/mL at Mean percent atresia data in longnose sucker were limStation 301 (Table 20). Female longnose sucker from Stations ited for YRB stations. Basinwide mean percent atresia was 

301, 305, and 308 with concentrations of vtg >7.0 mg/mL 0.0%, and station means ranged from 0.0% at Stations 304 and 

were stage-2 and -3 fish. Most female longnose sucker (67%) 305 to 0.5% at Stations 301 and 306 (Table 20). Two longhad concentrations of vtg between 0.4 and 7.4 mg/mL (Fig. nose sucker from Station 301 had atresia >2% (Fig. 21). YRB 

21). Concentrations of vtg in longnose sucker from near Cres- station means did not differ significantly for percent atresia 
60 Environmental Contaminants and their Effects on Fish

pg/mL pg/mL mg/mL %

2.0

1.5

1.0

0.5

0.0 0.25

0.20

0.15

0.10

0.05

0.00

3000

2500

2000

1500

1000

500

0 2500

2000

1500

1000

500

0

30

25

20

15

10

5

0

GSI

vtg

E2

KT

E/KT

301 302 303 304 305 306 307 308 309 310

Station

Figure 19. Reproductive health indicators by station in male northern pike collected in the Yukon River Basin in 2002. Indicators 

include gonadosomatic index (GSI), vitellogenin (vtg), estradiol 

(E2), 11-ketotestosterone (KT), and E/KT ratio. Shown for each 

group are points representing individual fish and the mean (red 

horizontal line), median (black horizontal line), interquartile range 

(box), and the 10th and 90th percentiles (whiskers). Stations are 

ordered upstream to downstream. See Table 1 for station descriptions. 

(Table 13). Similar percent atresia was reported in largescale 

sucker from the CRB (Hinck and others, 2004). No other 

studies evaluating percent atresia in longnose sucker were 

located.

Female and male longnose sucker were examined 

separately for steroid hormones because gender influenced 

concentrations of E2 and E/KT ratio (Table 13). The basinwide mean of E2 in female longnose sucker (1,402 pg/mL) 

was greater than in female northern pike (1,111 pg/mL) (Table 

21). Station means for concentrations of E2 in female longnose sucker ranged from 1,126 pg/mL at Station 301 to 1,630 

pg/mL at Station 305 and did not vary significantly among stations (Tables 13 and 21). Concentrations of E2 were >2,000 

pg/mL in female longnose sucker from Stations 305, 306, and 

308 (Fig. 21). Female northern pike from Station 308 also had 

concentrations of E2 >2,000 pg/mL (Table 21). Most female 

longnose sucker (81%) had concentrations of E2 between 500 

and 2,000 pg/mL (Fig. 21).

Concentrations of KT were less than those of E2 in most 

female longnose sucker. The basinwide mean concentration 

of KT in female longnose sucker was 361 pg/mL (Table 21). 

Station means for KT ranged from 298 pg/mL at Station 304 

to 440 pg/mL at Station 306, which were less than concentrations of KT measured in female northern pike (Table 21). 

Station means for concentrations of KT in female longnose 

sucker were <1,000 pg/mL (Table 21) and did not differ significantly (Fig. 21; Table 13). Mean E/KT ratios ranged from 

3.49 at Station 301 to 7.46 at Station 308, and only two female 

longnose sucker (6%) from Stations 301 and 306 had E/KT 

ratios <1.0 (Fig. 21). Other studies reporting concentrations of 

steroid hormones in female longnose sucker were not found.

Male Longnose Sucker

Male longnose sucker were collected from only four stations in the YRB; therefore, the reproductive stage data was 

limited (n=14) (Fig. 20). Male longnose sucker were identified as stage 0 (14%), stage 1 (29%) and stage 3 (57%). 

Basinwide mean GSI in male longnose sucker (1.7%) 

was less than in female longnose sucker (3.0%). Station 

means for GSI in male longnose sucker ranged from 0.4% at 

Stations 306 and 308 to 1.9% at Station 305 (n=1) (Table 20; 

Fig. 22). Male longnose sucker with GSI >1% at Station 305 

were identified as stage 3. GSI in male longnose sucker did 

not vary significantly among YRB stations (Table 13). Two 

longnose sucker from the upper CRB had GSI of 5.2% and 

5.3%, although gonadal stage was not determined (Hinck and 

others, 2004). 

Concentrations of vtg were >LOD (0.001 mg/mL) in 93% 

of male longnose sucker. The basinwide mean of vtg in male 

longnose sucker was 0.018 mg/mL, and station means ranged 

from 0.003 mg/mL at Station 301 to 0.020 mg/mL at Stations 

305 and 308 (Table 20, Fig. 22). Multiple male longnose 

sucker (73%) from Station 305 had concentrations of vtg 

>0.01 mg/mL (Table 20). These results may warrant further 
Results and Discussion 61

% 

100

90

80

70

60

50

40

30

20

10

0 M F 

1 7 

4 

F 

2 

M F

1 

2 

3 

8 

5 

1 

M F 

1 1 

1 

M F

1 6 

1 

M F 

301 302 303 304 305 306 307 308 309 310 Basin 

2 

4 

8 

1 

19 

6 

5 

6/5/02-6/6/02 6/4/02-6/7/02 5/30/02-5/31/02, 

6/28/02, 10/10/02 

6/4/02-6/6/02 6/10/02-6/14/02 

Stage 5 

Stage 3 

Stage 2 

Stage 1 

Stage 0 

Station 

Figure 20. Gonadal stage of female and male longnose sucker collected in the Yukon River Basin in 2002. Shown are the percentages 

(y-axis) and sample sizes (within the bars) of fish in each stage. The collection dates for each station are also shown. Stations are 

ordered upstream to downstream. See Table 1 for station descriptions.

investigation of endocrine modulating chemicals at this site. 

Concentrations of vtg in longnose sucker collected near Creston, Montana (0.006 mg/mL) and Grand Coulee, Washington 

(<0.005 mg/mL) were similar to concentrations in YRB longnose sucker (Hinck and others, 2004). The basinwide mean 

concentration of vtg in male largescale sucker from the CRB 

was 0.016 mg/mL, and station means ranged from <0.005 to 

0.05 mg/mL (Hinck and others, 2004). Other studies examining vtg in male longnose sucker were not located.

The basinwide mean of KT in male longnose sucker was 

755 pg/mL, and station means ranged from 131 pg/mL at Station 308 to 848 pg/mL at Station 305 (Table 21). Concentrations of KT in male longnose sucker did not vary significantly 

among stations (Table 13). Several male longnose sucker from 

Station 305 had concentrations of KT >1,200 pg/mL (Fig. 22).

Concentrations of E2 were less than those of KT in most 

male longnose sucker. The basinwide mean was 632 pg/mL 

in male longnose sucker, and station means for E2 ranged 

from 246 pg/mL at Station 301 to 2,459 pg/mL at Station 306 

(Table 21). Stations did not vary significantly in concentrations of E2 in male longnose sucker (Fig. 22; Table 13). Two 

male longnose sucker from Stations 305 and 306 had concentrations of E2 >2,000 pg/mL (Fig. 22). Station mean E/KT 

ratios ranged from 0.38 at Station 301 to 5.25 at Station 306, 

and male longnose sucker (29%) from Stations 306, 306, and 

308 had E/KT ratios >1.0 (Fig. 22). Other studies evaluating 

steroid hormones in male longnose sucker were not found.

One longnose sucker, with no preserved gonad from 

Station 305, had a GSI of 0.54% and a concentration of vtg of 

0.004 mg/mL. Concentrations of E2 and KT for this fish were 

206 pg/mL and 241 pg/mL of KT, respectively resulting in an 

E/KT ratio of 0.85.

Reproductive Biomarker: Summary

The reproductive biomarkers used in this study including gonadal histopathology, GSI, vtg, and steroid hormones 

are the best techniques available for measuring reproductive function as well as the effects of contaminants, whether 

endocrine disrupting or on general reproductive health. Age, 

species, water temperature, photoperiod, and other biotic and 

abiotic factors can influence these biomarkers and can cause 

great fluctuations during the reproductive cycle. Designing a 

study to control for these variables may provide valuable data 
62 Environmental Contaminants and their Effects on Fish

16 GSI 4 GSI

12

3

8

pg/mL pg/mL %

mg/mL %

2 4

pg/mL pg/mL mg/mL %

0 1

12 vtg

10 0 0.05 vtg 8

6 0.04

4

0.03

2

0 0.02

3.5 atresia

3.0 0.01

2.5

2.0 0.00

3000 E2 1.5

1.0 2500

0.5 2000

0.0

3000 1500 E2

2500 1000

2000 500

1500 0

1000 1600 KT

1400

500 1200

0 1000 KT 1000

800 800

600

600

400

400 200

0 200 8 E/KT

0

20 E/KT 6

15

4

10

2

5

0 0 301 302 303 304 305 306 307 308 309 310 301 302 303 304 305 306 307 308 309 310 Station Station

Figure 21. Reproductive health indicators by station in female Figure 22. Reproductive health indicators by station in male longlongnose sucker collected in the Yukon River Basin in 2002. 

Indicators include gonadosomatic index (GSI), vitellogenin (vtg), 

atresia, estradiol (E2), 11-ketotestosterone (KT), and E/KT ratio. 

Shown for each group are points representing individual fish and 

the mean (red horizontal line), median (black horizontal line), interquartile range (box), and the 10th and 90th percentiles (whiskers). 

Stations are ordered upstream to downstream. See Table 1 for 

station descriptions. 

nose sucker collected in the Yukon River Basin in 2002. Indicators 

include gonadosomatic index (GSI), vitellogenin (vtg), estradiol 

(E2), 11-ketotestosterone (KT), and E/KT ratio. Shown for each 

group are points representing individual fish and the mean (red 

horizontal line), median (black horizontal line), interquartile range 

(box), and the 10th and 90th percentiles (whiskers). Stations are 

ordered upstream to downstream. See Table 1 for station descriptions. 
63

and important insights into reproductive health. A variety of 

laboratory studies, as well as several field studies designed 

to monitor the effects of environmental contaminants on the 

reproductive activity, have proven these biomarkers to be 

valuable measures of reproductive activity and dysfunction. 

The use of this suite of reproductive biomarkers is necessary 

to evaluate the effects of contaminants on reproductive health 

and will continue to be incorporated into the BEST LRMN 

projects.

GSI is often used to evaluate reproductive status and 

health, although interpretations of GSI measurements rely on 

understanding natural variations among fish of the same age, 

gender, and species. Environmental influence and behavioral 

patterns may also confound the data. Considerable variations 

in gonad size have been reported throughout the reproductive cycle of many animal species (de Vlaming and others, 

1981). Northern pike from Station 310 consistently had GSI 

(>10%) greater than other stations; however, all northern pike 

were stage-4 and greater GSI are expected. Fish from Station 

310 were collected earlier (early May) than the other stations 

(June to October). Individual fish from Station 302 had the 

greatest GSI (1.5%) for male northern pike and were identified 

as stage-3 (late spermatogenic). Female and male longnose 

sucker from Station 305 had the greatest GSI (6.4% and 1.9%, 

respectively) in the YRB.

Gonadal histopathology was used to confirm gender, 

assign reproductive stage, and detect anatomical abnormalities 

such as the presence of ovotestis and excessive oocyte atresia. 

Gonadal stage varied between genders and stations, most 

likely a result of collection date. Stage was given close attention in the interpretation of these data because the reproductive biomarkers used in this study are known to vary over the 

course of the reproductive cycle. Ovotestes were not found 

in any fish from the YRB examined histologically, although a 

previous study reported ovotestis in northern pike from a Missouri River reservoir (June, 1977).

Oocyte atresia is defined as the involution or resorption 

of oocytes by the ovaries and has been sufficiently validated as 

a histological biomarker. Although oocyte atresia is a normal 

physiological event in all fish, it can become a pathological condition following exposure to certain environmental 

contaminants (Cross and Hose, 1988; 1989; Johnson and 

others, 1988; Kirubagaran and Joy, 1988). Several studies 

had examined oocyte atresia in northern pike (June, 1970; 

1977), but no studies were located for longnose sucker. Mean 

percent atresia was low in northern pike and longnose sucker 

and varied little among stations (Table 20). Oocyte atresia in 

northern pike and longnose sucker in the YRB did not indicate 

exposure to environmental contaminants.

Relatively low concentrations of vtg were measured in 

both northern pike and longnose sucker in the YRB. Concentrations of vtg in female northern pike were similar among 

stations with most fish having concentrations <3.0 mg/mL. 

Female longnose sucker had greater concentrations of vtg 

(most ranging from 2 to 10 mg/mL) compared to female 

northern pike. Other studies have localized vtg receptors to 

Results and Discussion

the testes, muscle, and spermatocytes (Bidwell and Carlson, 

1995; Tao and others, 1996). A 1995 reconnaissance study 

by Goodbred and others (1997) reported detectable concentrations of vtg in males from a reference site and confirmed 

the fact that small amounts of vtg can be present in healthy 

males. Vitellogenin was measured in male northern pike from 

all stations except Stations 304, 305 (no male northern pike 

collected), and 307; concentrations of vtg were <0.20 mg/mL. 

Male northern pike from Stations 301 and 308 had the greatest 

concentrations of vtg (>0.1 mg/mL). Male longnose sucker 

from Stations 305, 306, and 307 had concentrations of vtg 

>0.05 mg/mL. Concentrations of vtg were not correlated with 

stage and did not differ significantly among stages for fish collected in the YRB.

E2, KT, and E/KT were examined in northern pike and 

longnose sucker from the YRB to determine if chemical 

compounds were affecting steroid hormones concentrations. 

Like many of the other reproductive biomarkers, concentrations of steroid hormones can vary by gender, age, geographical locations, species, and season (Barry and others, 1990; 

Bromage and others, 1982; Chang and Chen, 1990; Denslow 

and others, 1999; Down and others, 1990; Goodbred and 

others, 1997; So and others, 1989); therefore, interpretation 

of hormone data requires knowledge of all of these factors. 

Other studies reporting steroid hormone data in northern pike 

and longnose sucker were not found; therefore, “normal” 

concentrations of steroid hormones in these species cannot be 

determined. However, E/KT ratios >1.0 for females and <1.0 

for males are generally considered normal (Folmar and others, 

1996; Hileman, 1994). Female northern pike from all stations 

except Station 301 had individual fish with E/KT ratios <1.0, 

and male northern pike from all stations except Stations 301 

and 303 had E/KT ratios >1.0 (Table 21). Gonadal stage did 

not influence steroid hormone concentrations in northern pike. 

Individual female longnose sucker from Stations 301 and 306 

had E/KT ratios <1.0, and male longnose sucker from Stations 

305, 306, and 307 had E/KT ratios >1.0 although sample sizes 

were limited (Table 21). Unlike northern pike, gonadal stage 

influenced steroid hormone concentrations in longnose sucker. 

The variation in hormones concentrations within each species 

was expected because of the various factors that influence 

these reproductive biomarkers and has been reported in others 

species (McDonald and others, 2002).

Spatial patterns in contaminant concentrations

and biomarker responses

Geographic Summaries

Geographic station summaries were made to highlight elevated contaminant concentrations and/or biomarker 

responses or both (Table 22). The highlighted findings indicate contaminant concentrations or EROD levels that exceeded 
64 Environmental Contaminants and their Effects on Fish

known thresholds or were anomalous (that is, high or low) 

relative to other YRB stations. The colors for the reproductive 

and fish health biomarkers are relative and indicate the number 

and/or magnitude of the anomalies (including the number of 

gender-species categories in which they occurred) at a station. 

The summaries are intended only to draw attention to particular stations highlighted in the text, possibly for further investigation. It is important to recognize that increased frequencies 

of external lesions or elevated HAI scores, which represent 

the cumulative total number of grossly visible internal and 

external lesions, do not necessarily indicate direct contaminant 

effects. Many factors other than contaminants can indirectly 

influence fish health indicators and reproductive biomarkers, 

including nutrients or organic matter and water temperature. 

Considerably more is known about risk to fish and piscivorous wildlife associated with bioaccumulative contaminants 

and EROD than about long- and short-term risks represented 

by the other biomarkers. Therefore, greater relative risk has 

been associated with elevated contaminant concentrations and 

EROD rates than with anomalous fish health or reproductive 

biomarkers (Table 22; Figs. 23-25).

Station 301 (Near Charley-Kandik confluence, AK)

Station 301 was located near the confluence of the Charley and Kandik Rivers with the Yukon River near the Canadian 

border. Female and male northern pike and longnose sucker 

were collected in early June 2002. Few contaminants and 

biomarkers exceeded threshold criteria or appeared anomalous in fish at this site (Table 22). The concentration of Se 

in male northern pike (0.66 μg/g ww) and female longnose 

sucker (0.62 μg/g ww) exceeded guidelines to protect fish 

and piscivorous wildlife (Fig. 23; Lemly, 1996). Male and 

female northern pike and female longnose sucker had the 

greatest station mean EROD activity in the YRB. Even so, 

EROD activity sample sizes were small at Station 301, and 

other stations had individual fish with greater EROD activities. 

Only two fish health indicators and reproductive biomarkers 

were highlighted at Station 301 (Table 22). Mean SSI in male 

northern pike (0.18%) was the greatest in the YRB. A male 

northern pike had the greatest concentration of vtg (0.194 

mg/mL) measured in the YRB (Fig. 24), suggesting this fish 

may have been exposed to endocrine-modulating chemicals. 

Multiple contaminants and biomarkers were highlighted in 

male northern pike from Station 301; however, only two male 

northern pike were collected and caution should be used when 

interpreting these data.

Station 302 (Fish Hook Bend, AK)

Station 302 was located near Fish Hook Bend on the 

upper Porcupine River. Male and female northern pike were 

collected from this site in mid-August 2002. Selenium was 

the only contaminant of concern at this station. Concentrations of Se in male (0.72 μg/g ww) and female (0.73 μg/g ww) 

northern pike exceeded guidelines to protect fish and piscivorous wildlife (Fig. 23; Lemly, 1996). Fish health indicators 

were not anomalous in fish from this station. Atresia was the 

only reproductive biomarker highlighted (Table 22). Two 

female northern pike had atresia ≥8% whereas the others had 

≤4%; all female northern pike from this site were stage 2. The 

differences in the atresia data from this site could be a result of 

normal, natural variation in northern pike.

Station 303 (Fort Yukon, AK)

Station 303 was located on the lower Porcupine River 

upstream of its confluence with the Yukon River. Male and 

female northern pike were collected from this site in mid-June 

2002. Concentrations in northern pike did not exceed threshTable 22. Summary of chemical and biological indicator results by Yukon River Basin station. Within each column, colors indicate 

the severity, prevalence, or both of the indicated condition or conditions at each station (green<yellow<red). These designations 

are relative; see text for explanations. Male and female northern pike (p), longnose sucker (s), and burbot (b) were collected from 

all sites unless otherwise indicated. See Table 3 and Figure 1 for station locations. Bold lettering denotes that threshold criteria 

were exceeded and/or high incidence of elevated occurrence. Hg, mercury; Se, selenium; EROD, ethoxyresorufin O -deethylase; 

EL, external lesions; SSI, splenosomatic index; HAI, health assessment index; MA, macrophage aggregates (one or more 

parameters); vtg, vitellogenin; E/KT, estradiol/11-ketotestosterone ratio; m, male; f, female. For SSI, - indicates smaller; all others 

larger. 

Station Species Collected Contaminants and EROD Fish Health 

Indicators 

Reproductive 

Biomarkers 

Charley-Kandik, AK (301) p, s Se (mp,fs), EROD (mp,fp,fs) SSI (mp) vtg (mp) 

Fish Hook Bend, AK (302) p Se (mp,fp) atresia (fp) 

Fort Yukon, AK (303) p EL (p), HAI (p) E/KT (fp) 

The Bridge, AK (304) p, fs Hg (mp,fp), Se (fs) atresia (fp), E/KT (mp,fp) 

Fairbanks, AK (305) fp, s, b Hg (mb), Se (mb,fb,fs) vtg (ms), E/KT (ms) 

Tolovana, AK (306) p, s Hg (fp) SSI (fp, -s), MA (p) E/KT (mp,fp,ms) 

Tanana, AK (307) p Hg (mp,fp) HAI (p) 

Galena, AK (308) p, s Hg (mp,fp) SSI (fp) vtg (mp,ms), E/KT (mp) 

Innoko, AK (309) p vtg (mp), E/KT (fp) 

Kotlik, AK (310) p, mb E/KT (fp) 
YUKO

N TERRITOR

Y

YUKON TERRITOR

Y

Results and Discussion 65

old criteria for any chemical contaminant at Station 303 (Table 

22). External lesions and HAI in northern pike were the highest in the YRB. Most abnormalities were attributed to cuts or 

abrasions on the body surface which are typical in predatory ALASKA

302 fish like northern pike. The lesions could result from natural 

$T processes and are not indicative of exposure to environmental 303

$T contaminants.

Station 304 (Near the Bridge, AK)

304

%U 301 $T

308 %U %U % 307 306 U %U

305 

T$ $T

309 310 

Station 304 was located on the Ray River near its confluence with the Yukon River near the Bridge. Male and female 

northern pike and female longnose sucker were collected from 

this site in early June 2002. Few contaminants and biomarkers exceeded threshold criteria or appeared anomalous at this 

site (Table 22). Concentrations of Hg in female (0.46 μg/g 

ww) and male (0.56 μg/g ww) northern pike exceeded criteria 

(0.3 μg/g ww) shown to cause reproductive impairment in 

loons (Fig. 23; Barr, 1986). The concentration of Se in female 

longnose sucker (0.60 μg/g ww) approached guidelines to 

protect fish and piscivorous wildlife (Fig. 23; Lemly, 1996). 

Fish health indicators were not anomalous in fish at Station 

304, but two reproductive biomarkers were highlighted. Two 

female northern pike had atresia ≥8% whereas other fish 

had ≤2%. These differences in the atresia data could reflect 

Hg (μg/g)

<0.1

0.1-0.3

>0.3

ALASKA

302 

$T#

303 natural variation in northern pike. Several female northern 

pike had E/KT ratios <1.0, and one male northern pike had an 

E/KT ratio of 7.66 (Fig. 25). The female northern pike with 

an E/KT ratio of 0.22 also had 9% atresia in the ovaries. These 

results may indicate isolated occurrences of reproductive stress 

#S#

30

$T

4 

# 301 $T#

#

308 #S #S#

306 %U

#

305 307 #S#

#S#

S##

309 310 

for some fish at Station 304.

Station 305 (Fairbanks, AK)

Station 305 was located on the Tanana River downstream 

of Fairbanks. Female northern pike, male and female longnose sucker, and male and female burbot were collected in late 

May, late June, and mid-October 2002. Few contaminants and 

biomarkers exceeded threshold criteria or appeared anomalous 

at this site (Table 22). The concentration of Hg in male burbot 

was 0.30 μg/g ww, the concentration shown to cause reproductive impairment in loons (Fig. 23; Barr, 1986). Concentrations 

of Se in female longnose sucker (0.61 μg/g ww), male burbot 

(0.85 μg/g ww), and female burbot (0.69 μg/g ww) exceeded 

guidelines to protect fish and piscivorous wildlife (Fig. 23; 

Lemly, 1996). The concentration of Se in male burbot was the 

maximum measured in the YRB. Two reproductive biomarkers were anomalous at Station 305: eight of 11 (73%) male 

longnose sucker had concentrations of vtg >0.01 mg/mL (Fig. 

24), and four (36%) male longnose sucker had E/KT ratios 

>1.0 (Fig. 25). However, vtg was not detected (>0.001 mg/

mL) in the male longnose sucker with the greatest E/KT ratio 

(7.17). These results indicate that some fish were exposed to 

endocrine-modulating chemicals.

Se (μg/g)

<0.6

0.6-0.8

>0.8

Figure 23. Maximum concentrations (μg/g ww) of mercury (Hg, 

upper panel) and selenium (Se, lower panel) in composite samples 

of whole fish. A concentration of Hg of 0.1 μg/g ww in fish has 

been suggested as a guideline for the protection of piscivorous 

mammals (Yeardley and others, 1998), and concentrations of 0.3 

μg/g ww cause reproductive impairment in the common loon 

(Gavia immer) (Wiener and Spry, 1996; Wiener and others, 2002). 

Concentrations of Se should be <0.6 μg/g ww to avoid toxicity 

to piscivorous wildlife and <0.8 μg/g ww to avoid toxicity to fish 

(Lemly, 1996). See Table 1 for station descriptions.
YUKON TERRITORY

YUKON TERRITORY

66 Environmental Contaminants and their Effects on Fish

female northern pike had E/KT ratios <1.0, and several male 

northern pike and one male longnose sucker had an E/KT ratio 

>1.0 (Fig. 25). These results suggest isolated occurrences of 

ALASKA biomarker responses to environmental contaminants.

302 

%U

#

303 %U

#

304 

# 301 #S Station 307 (Tanana, AK)

Station 307 was located on the Tanana River upstream of 

its confluence with the Yukon River near the village of Tanana.

%U

#

#

% #

S 308 #S %U #

U

#

307 306 305 

%U

#

U%

#

309 310 

Male and female northern pike were collected from this site in 

early June 2002. Few contaminants and biomarkers exceeded 

threshold criteria or appeared anomalous at this site (Table 

22). Concentrations of Hg in female (0.37 μg/g ww) and male 

(0.42 μg/g ww) northern pike exceeded criteria (0.3 μg/g ww) 

shown to cause reproductive impairment in loons (Fig. 23; 

Barr, 1986). Multiple northern pike from Station 307 had HAI 

>100, mostly attributed to discolored liver and abrasions on 

the body surface. Northern pike were infected with a number 

of organisms including Ichthyophonus, hepatic biliary myxosporidians, and kidney tubular myxosporidians. There was no 

evidence to suggest biomarkers were altered at Station 307.

Station 308 (Galena, AK)

vtg (mg/mL): Northern pike (males)

<0.01

≥0.01

No Data

ALASKA

302 

S#

303 Station 308 was located on the Yukon River near the village of Galena. Male and female northern pike and longnose 

sucker were collected from this site in mid-June 2002. Several 

contaminants and biomarkers exceeded threshold criteria 

or appeared anomalous at this site (Table 22). ConcentraS#

304 

# 301 S #S#

308 #

S #S#

#

U% 307 306 # %U

305 

S#

S#

309 310 

tions of Hg in female (0.34 μg/g ww) and male (0.33 μg/g 

ww) northern pike exceeded criteria (0.3 μg/g ww) shown to 

cause reproductive impairment in loons (Fig. 23; Barr, 1986). 

Female northern pike from Station 308 had SSI values consistently greater than other YRB stations. Six of 12 (50%) male 

northern pike and one male longnose sucker had concentrations of vtg >0.01 mg/mL (Fig. 24). Two male northern pike 

had E/KT ratios >1.0 (Fig. 25). However, male northern pike 

with the greatest E/KT ratio (28.4) did not have a high concentration of vtg (0.018 mg/mL). These results indicate isolated 

occurrences of reproductive stress for some fish at Station 308.

Station 309 (Innoko NWR, AK)

Station 309 was located on the Innoko River near the 

Innoko NWR Field Station. Male and female northern pike 

were collected in mid-July 2002. Concentrations of contaminants measured in northern pike did not exceed threshold 

criteria or appeared anomalous at Station 309 (Table 22). 

Vitellogenin in male northern pike and E/KT ratio in female 

northern pike were highlighted at this station. Concentrations 

of vtg were >0.01 mg/mL in 6 of 11 (55%) male northern pike 

from Station 309, indicating exposure to endocrine disrupting 

chemicals (Fig. 24). Several female northern pike had E/KT 

vtg (mg/mL): Longnose sucker (males)

<0.01

≥0.01

No Data

Figure 24. Plasma vitellogenin (vtg) in male northern pike (upper 

panel) and longnose sucker (lower panel). See Table 1 for station 

descriptions.

Station 306 (Tolovana, AK)

Station 306 was located on the Tanana River at its confluence with the Tolovana River. Male and female northern pike 

and longnose sucker were collected from this site in early June 

2002. Mercury and biomarkers exceeded threshold criteria or 

appeared anomalous at this site (Table 22). The concentration 

of Hg in female northern pike (0.69 μg/g ww) was the maximum measured in the YRB and exceeded criteria shown to 

cause reproductive impairment in loons (Fig. 23; Barr, 1986). 

Several fish health indicators were noted in fish at Station 306.

SSI values were consistently greater in female northern pike 

and less in longnose sucker than other YRB stations. Several 
YUKON TERRITOR

Y

YUKON TERRITOR

Y

Results and Discussion 67

lik. Male and female northern pike and one male burbot were 

collected in early May 2002. Organochlorines and elemental 

contaminants were below protective criteria in all fish samples.

ALASKA E/KT ratio was the only biomarker highlighted at this station 

302 (Table 22). Two female northern pike had E/KT ratios <1.0 

(Fig. 25), although reproductive stress does not appear to be 

widespread at Station 310.

$T

#

303 

%U

#

304 

#

301 %U #S#

#

308 %U %#

U #S#

U%

#

307 306 305 

%U

#

U%

#

309 310 Correlations Between Contaminant

Concentrations and Biological Endpoints

Spearman Rank correlations were examined to determine if chemical concentrations were related to biomarker 

responses in the YRB (Table 23). However, only Hg and Se 

were examined, because they were the only contaminants consistently measured >LOD. Significant correlations (P<0.05) 

were determined for each gender and species. Few biomarker 

responses were found to be correlated with Hg or Se and 

present in more than one species, gender, or both (Table 23). 

Mercury was correlated with age, length, and weight in female 

northern pike. This correlation was expected due to the bioaccumulative properties of Hg. MA-size in both male northern 

pike and longnose sucker increased with concentrations of Hg.

Mercury in male northern pike was also positively correlated 

with E2 and E/KT. The small sample size and range of conE/KT: Northern pike

Male <1.0 or Female >1.0

Male 1.0-2.0 or Female 0.5-1.0

Male >2.0 or Female <0.5

No Data

ALASKA

302 

S#

303 S#

304 

# 301 #S $T#

#

308 S %U#

#

U%#

307 306 %U

305 

S#

S#

309 310 

centrations limit the interpretation of the YRB data. 

Summary and Conclusions

Overall, few chemical contaminants or biological endpoints indicated poor fish health in northern pike, longnose 

sucker, or burbot collected from the YRB in 2002. Organochlorine contaminants in fish samples were <LOD at most 

stations, which is consistent with results from previous YRB 

studies (Schmitt and others, 1999b; Snyder-Conn, 1992). Fish 

samples with concentrations of Hg exceeding 0.3 μg/g ww and 

Se exceeding 0.6 μg/g ww were measured at several stations; 

these concentrations are potentially harmful to piscivorous 

wildlife (Lemly, 1996; Wiener and Spry, 1996; Wiener and 

others, 2002). However, no other chemical contaminants 

exceeded wildlife criteria in YRB fish. Concentrations of 

Hg in male and female northern pike in the mid-YRB from 

Stations 304 (The Bridge), 305 (Fairbanks), 306 (Tolovana), 

307 (Tanana), and 308 (Galena) exceeded protective criteria. 

Concentrations of Se exceeded criteria in fish samples from 

the upper YRB near the Canadian border at Stations 301 (near 

the Charley-Kandik confluence) and 302 (Fish Hook Bend), 

the mid-YRB at Station 304 (The Bridge), and near Fairbanks 

at Station 305. Concentrations of Hg and Se exceeding wildlife criteria were measured primarily in male northern pike and 

female longnose sucker. It is difficult to determine the source 

E/KT: Longnose sucker

Male <1.0 or Female >1.0

Male 1.0-2.0 or Female 0.5-1.0

Male >2.0 or Female <0.5

No Data

Figure 25. Ratio of estradiol to 11-ketotestosterone (E/KT) in 

northern pike (upper panel) and longnose sucker (lower panel). 

These ratios indicate female fish with low levels of estradiol and 

male fish with low levels of 11-ketotestosterone. See Table 1 for 

station descriptions.

ratios <1.0 (Fig. 25). These results suggest isolated occurrences of reproductive stress for some fish at Station 309.

Station 310 (Kotlik, AK)

Station 310 was located on the north mouth of the Yukon 

River 7 km upstream of the Bering Sea near the village of Kot-
68 Environmental Contaminants and their Effects on Fish

Table 23. Significant Spearman rank correlations (P <0.05)

between biomarkers and contaminants. See text for biomarker 

definitions. Black text, positive correlations; bold italicized 

text, negative correlations. Genders were not combined in this 

analysis because many biomarker differed between males and 

females.

Biomarker Hg Se 

Age female pike 

Total Length female pike 

Weight female pike 

MA-size male sucker, male pike female sucker 

MA-# male sucker 

E2 female sucker, male pike 

E/KT male sucker, male pike 

EROD male pike 

or origin of Hg and Se in northern pike because it is a migratory species, and longnose sucker is believed to swim randomly in streams (Mueller and others, 1996). However, most 

Se is believed to enter the Yukon River system through the 

natural weathering of rocks. Atmospheric deposition is one of 

the main contributors of Hg in the YRB and other Arctic areas 

(NCP, 2003).

Dioxin-like activity as measured by TCDD-EQs and 

EROD activity were unremarkable in the YRB. Dioxin-like 

activity was <LOD in YRB fish samples, which is consistent with a previous dioxin study in the basin (Snyder-Conn, 

1992). EROD activity was generally low in fish from all YRB 

stations. Station 301 (near the Charley-Kandik confluence) 

had the greatest station mean for male northern pike (17.51 

pmol/min/mg), female northern pike (8.57 pmol/min/mg), 

male longnose sucker (10.03 pmol/min/mg), and female 

longnose sucker (8.78 pmol/min/mg). However, the EROD 

activities in these fish were less than previous EROD data for 

these species in past BEST LRMN investigations (Schmitt and 

others, 2002a; Hinck and others, 2004). Factors other than 

contaminant exposure such as water temperature and nutrition 

may be responsible for the slightly higher EROD activities at 

Station 301.

Our study is the first to examine an extensive suite of biomarkers in relation to environmental contaminants in fish from 

the YRB. Fish health indicators and reproductive biomarkers did not indicate widespread responses to contaminants, 

but individual fish throughout the basin expressed isolated 

responses. Isolated occurrences of enlarged spleens (Stations 

301, 306, and 308) and prevalence of external lesions (Station 

303) in northern pike are likely attributed to factors such as 

age, size, growth rate, and gonadal development (Krykhitin, 

1976; Ruklov, 1979), although these conditions have also 

been reported as consequences of immune suppression caused 

by chemical exposure (Anderson and others, 1989; Hutchinson and Manning, 1996). The latter explanation is unlikely 

because MA density, size, and percent tissue occupied were 

similar among stations for each species, although northern 

pike from Station 306 (Tolovana) did have greater MA densities compared to the other YRB stations. 

Concentrations of vtg >0.01 mg/mL are not typical in 

male fish and may indicate an estrogenic response to environmental conditions. Concentrations of vtg were >0.01 mg/mL 

in multiple male fish from Stations 301 (near the CharleyKandik confluence), 305 (Fairbanks), 308 (Galena), and 309 

(Innoko). Steroid hormone concentrations (E2 in female fish 

and KT in male fish) were low in northern pike, longnose 

sucker, or both from Stations 303 (Fort Yukon), 304 (The 

Bridge), 305 (Fairbanks), 306 (Tolovana), 308 (Galena), 309 

(Innoko), and 310 (Kotlik). However, many factors such as 

season, gender, and geographical location can affect circulating steroid hormone levels in fish (see review in Schmitt and 

Dethloff, 2000). 

Overall, we determined there was no evidence to indicate 

that fish from the YRB had been exposed to high concentrations of environmental contaminants. Similar conclusions 

have been reported other U.S. river basins (Hinck and others, 

2004; Schmitt, 2002a; Schmitt and others, 2004). The YRB 

is unique in that it is largely undisturbed by population and 

industrial centers and is considered pristine compared to other 

U.S. river basins. Nevertheless, these current attributes may 

change in the future, resulting in the degradation of water 

quality and aquatic habitat within the YRB. Therefore, results 

from our study may provide reference or baseline data on 

environmental contaminants and their effects in fish for future 

investigations in the YRB. 

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82 Environmental Contaminants and their Effects on Fish
Appendix 1 83

Appendix 1
84 Environmental Contaminants and their Effects on Fish

Appendix 1. Nominal Method Detection Limits (MDL) and results of quality assurance (QA) for 

organochlorine chemicals (ng/g ww) analyzed in whole body fish composites collected in the Yukon 

River Basin in 2002. 

Fortified Spike Percent Recoveries Analyte 

#1 #2 #3 #4 

MDL 

Mean ng/g ww

Pentachlorobenzene 106 95 90 93 96 0.1 

Hexachlorobenzene 96 99 97 99 98 2.1 

Pentachloroanisole 48 118 118 114 100 0.2 

Alpha-BHC 81 85 80 87 83 0.2 

Beta-BHC 52 64 45 57 54 0.2 

Lindane 54 86 69 78 72 0.4 

Delta-BHC 81 78 47 72 70 0.1 

Heptachlor 92 64 68 39 65 0.2 

Heptachlor epoxide 70 73 70 78 73 0.2 

Aldrin 85 97 81 100 91 0.3 

Dacthal 26 96 81 99 75 0.3 

Dieldrin 108 78 72 84 85 0.2 

Endrin 80 21 33 59 48 0.1 

Oxychlordane 100 98 106 112 104 0.1 

cis-Chlordane 91 87 78 85 85 0.2 

trans-Chlordane 101 85 84 86 89 0.3 

cis-Nonachlor 71 81 79 87 79 0.1 

trans-Nonachlor 74 99 87 93 88 0.2 

o,p'-DDE 83 74 75 79 78 0.2 

o,p'-DDD 79 92 66 84 80 0.7 

o,p'-DDT 89 94 79 94 89 0.1 

p,p'-DDE 125 80 80 81 91 0.4 

p,p'-DDD 77 89 90 95 88 0.4 

p,p'-DDT 75 129 125 137 117 1.4 

Endosulfan I 106 89 77 96 92 0.3 

Endosulfan II 123 87 63 86 90 0.2 

Endosulfate 95 96 104 99 99 0.8 

Methoxychlor 94 130 153 131 127 1.7 

Mirex 90 101 81 100 93 0.0 

Total PCBs 94 96 ND 86 92 20 

Total Toxaphene 90 95 73 86 86 11 
Appendix 2 85

Appendix 2
86

310 

Environmental Contaminants and their Effects on Fish

Appendix 2. Histological observations in northern pike, longnose sucker, and burbot collected in the 

Yukon River Basin in 2002. Total number of individual tissues examined (n), percentage with no 

significant lesions and percentages with selected lesions are presented for each station.—Continued 

Species, Organ, and Lesion 303 304 305 306 307 308 309

Station 

301 302 

Northern Pike 

Liver, n 6 20 22 9 3 20 20 20 21 17 

No significant lesions 83 65 36 44 100 45 65 65 29 53 

Biliary myxosporidians 17 0 0 22 0 0 20 0 0 47 

Ichthyophonus 0 0 0 0 0 0 5 0 0 0 

Nematodes 0 5 0 0 0 0 0 5 0 0 

Lymphocyte infiltrates 0 30 64 33 0 50 10 35 71 0 

Altered foci 0 0 0 0 0 0 0 0 5 0 

Fatty change 33 0 18 0 0 20 0 10 0 0 

Gill, n 6 18 22 7 1 19 19 20 21 17 

No significant lesions 17 22 73 43 0 42 16 20 33 46 

Trichodinid ciliates 83 0 9 43 100 37 68 55 5 6 

Monogenetic trematodes 17 78 5 14 0 0 32 30 24 27 

Myxosporidians 0 0 0 0 0 0 0 0 0 9 

Epithelial hyperplasia 17 33 9 0 0 5 6 20 38 6 

Anterior kidney, n 6 19 22 9 3 20 18 20 20 13 

No significant lesions 100 100 100 100 100 100 94 100 100 100 

Ichthyophonus 0 0 0 0 0 0 6 0 0 0 

Posterior kidney, n 6 20 22 9 3 20 20 20 21 17 

No significant lesions 0 30 27 11 67 5 10 25 62 0 

Myxosporidians 83 5 27 78 33 45 85 20 5 100 

Ichthyophonus 0 0 0 0 0 0 5 0 0 0 

Glomerular microsporidian 0 5 0 0 0 0 0 0 0 0 

Developing nephrons 33 70 64 22 0 90 25 70 33 6 

Nephrocalcinosis 33 0 0 0 0 20 0 0 0 6 

Spleen, n 6 20 22 9 3 20 20 20 20 17 

No significant lesions 83 100 100 100 100 100 100 90 100 100 

Lymphoid depletion 17 0 0 0 0 0 0 10 0 0 

Longnose sucker 

Liver, n 12 -- -- 2 21 3 8 -- --

No significant lesions 33 -- -- 0 38 33 13 -- --

Sanguinicolid trematode 50 -- -- 100 52 67 88 -- --

Granulomas 0 -- -- 0 5 0 0 -- --

Fatty change 17 -- -- 0 0 0 0 -- --

Bile duct hyperplasia 0 -- -- 0 0 33 0 -- --

Gill, n 12 -- -- 1 20 3 8 -- --

No significant lesions 25 -- -- 0 20 33 0 -- --

Trichodinid ciliates 0 -- -- 0 5 0 0 -- --

Chilodonella-like ciliate 0 -- -- 0 0 0 63 -- --

Epitheliocystis-like organism 8 -- -- 0 0 0 13 -- --

Sanguinicolid trematode 25 -- -- 0 25 0 50 -- --

Myxosporidians 25 -- -- 100 70 33 50 -- --

Epithelial hyperplasia 42 -- -- 0 35 33 25 -- --

Anterior kidney, n 12 -- -- 2 21 3 8 -- --

No significant lesions 100 -- -- 100 100 100 100 -- --

Posterior kidney, n 12 -- -- 2 21 -- 3 8 -- --

No significant lesions 25 -- -- 0 38 -- 67 38 -- --

Myxosporidians 8 -- -- 0 5 -- 0 0 -- --

Sanguinicolid trematodes 67 -- -- 50 57 -- 0 25 -- --

Developing nephrons 0 -- -- 0 0 -- 33 25 -- --

Nephrocalcinosis 17 -- -- 0 10 -- 0 0 -- --

Hyaline droplets 42 -- -- 100 10 -- 0 13 -- --

Spleen, n 12 -- -- 2 21 -- 3 8 -- --

No significant lesions 100 -- -- 100 86 -- 100 100 -- --

Sanguinicolid trematodes 0 -- -- 0 14 -- 0 0 -- --
Appendix 2 87

Appendix 2. Histological observations in northern pike, longnose sucker, and burbot collected in the 

Yukon River Basin in 2002. Total number of individual tissues examined (n), percentage with no 

significant lesions and percentages with selected lesions are presented for each station.—Continued 

Species, Organ, and Lesion 303 304 305 306 307 308 309 310

Station 

301 302 

Burbot 

Liver, n -- -- -- -- 12 -- -- -- -- 1 

No significant lesions -- -- -- -- 42 -- -- -- -- 0 

Nematodes -- -- -- -- 8 -- -- -- -- 0 

Granulomas -- -- -- -- 58 -- -- -- -- 100 

Gill, n -- -- -- -- 5 -- -- -- -- 1 

Trichodinid ciliates -- -- -- -- 60 -- -- -- -- 100 

Anterior kidney, n -- -- -- -- 9 -- -- -- -- 0 

No significant lesions -- -- -- -- 89 -- -- -- -- --

Granulomas -- -- -- -- 11 -- -- -- -- --

Posterior kidney, n -- -- -- -- 6 -- -- -- -- 0 

No significant lesions -- -- -- -- 17 -- -- -- -- --

Granulomas -- -- -- -- 17 -- -- -- -- --

Developing nephrons -- -- -- -- 33 -- -- -- -- --

Myxosporidians -- -- -- -- 67 -- -- -- -- --

Spleen, n -- -- -- -- 12 -- -- -- -- 1 

No significant lesions -- -- -- -- 75 -- -- -- -- 0 

Granulomas -- -- -- -- 25 -- -- -- -- 100 
Hinck, J.E.; Bartish, T.M.; Blazer, V.S.; Denslow, N.D.; Gross, T.S.; Myers, M.S.; Anderson, P.J.; Orazio, C.E.; and Tillitt, D.E..—Biomonitoring of Environmental 

Status and Trends (BEST) Program: Environmental Contaminants and their Effects on Fish in the Yukon River Basin USGS—SIR-2004—5285

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