Report prepared for Wrangell-St. Elias National Park and Preserve

Mercury in Fishes from Wrangell-St. Elias National 

Park and Preserve, Alaska

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2014–1145
Cover: Photograph of Mount Drum, Wrangell-St. Elias National Park and Preserve, 2007.

Photograph taken from the Tok Cutoff by J. Willacker, U.S. Geological Survey.
Mercury in Fishes from Wrangell-St. Elias National Park and 

Preserve, Alaska

By Brandon M. Kowalski, James J. Willacker, Jr., Christian E. Zimmerman, and Collin A. Eagles-Smith

Report prepared for Wrangell-St. Elias National Park and Preserve

Open-File Report 2014–1145

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014 

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Suggested citation:

Kowalski, B.K., Willacker, J.J., Zimmerman, C.E., and Eagles-Smith, C.A., 2014, Mercury in fishes from Wrangell-St. 

Elias National Park and Preserve, Alaska: U.S. Geological Survey Open-File Report 2014-1145, 26 p., 

http://dx.doi.org/10.3133/ofr20141145.

ISSN 2331-1258 (online)

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endorsement by the U.S. Government. 

Although this information product, for the most part, is in the public domain, it also may contain

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secured from the copyright owner. 
iii

Contents

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

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

Methods......................................................................................................................................................................... 2

Study Sites and Sample Collection ............................................................................................................................ 2

Sample Preparation ................................................................................................................................................... 5

Otolith Removal and Preparation ............................................................................................................................... 5

Mercury Determination............................................................................................................................................... 5

Statistical Analyses .................................................................................................................................................... 6

Toxicological Risk Estimation..................................................................................................................................... 7

Results........................................................................................................................................................................... 8

Species Comparisons ...............................................................................................................................................13

Site Comparisons......................................................................................................................................................14

Toxicological Risks ...................................................................................................................................................15

Fish Risk ...............................................................................................................................................................15

Avian Risk .............................................................................................................................................................17

Human Consumption Risk.....................................................................................................................................17

Discussion ....................................................................................................................................................................18

Acknowledgments ........................................................................................................................................................20

References Cited..........................................................................................................................................................21

Appendix 1. Equations for Converting Standard Length (SL, in millimeters) to Total Length (TL, in millimeters) 

for Four Species of Fish Sampled from Wrangell-St. Elias National Park and Preserve, Alaska..................................25

Appendix 2. Size at Which the Proportion of Modeled Individuals of Each Species from Tanada Lake 

Exceeded Defined Toxicity Benchmarks in Wrangell-St. Elias National Park and Preserve, Alaska ............................26
iv

Figures

Figure 1. Schematic of four study lakes in Wrangell-St. Elias National Park and Preserve, Alaska.............................. 3

Figure 2. Arithmetic-mean total mercury concentrations (THg, in nanograms per gram wet weight [ng/g ww]) ±1 

standard error in fish species collected from four lakes in Wrangell-St. Elias National Park and Preserve, Alaska....... 9

Figure 3. Linear relationships between standard length (in millimeters, [mm]) and total mercury concentrations 

(THg, in nanograms per gram dry weight [ng/g dw]) in fish muscle of (A) Arctic grayling, (B) burbot, (C) lake trout, 

and (D) rainbow trout sampled from Wrangell-St. Elias National Park and Preserve, Alaska...................................... 10

Figure 4. Linear relationships between fish age (in years) and total mercury concentrations (THg, in 

nanograms per gram dry weight [ng/g dw]) in fish muscle of (A) Arctic grayling, (B) burbot, (C) lake trout, and

(D) rainbow trout sampled from Wrangell-St. Elias National Park and Preserve, Alaska............................................. 11

Figure 5. Logarithmic relationships between fish age (in years) and standard length (in millimeters [mm]) of 

(A) Arctic grayling, (B) burbot, (C) lake trout, and (D) rainbow trout sampled from Wrangle-St. Elias 

National Park and Preserve, Alaska ............................................................................................................................ 12

Figure 6. Back-transformed least-square mean total mercury concentrations (THg, in nanograms per gram wet 

weight [ng/g ww]) in muscle of fishes from Tanada Lake, Wrangell-St. Elias National Park and Preserve, Alaska..... 13

Figure 7. Back-transformed least-square mean total mercury concentrations (THg, in nanograms per gram 

wet weight [ng/g ww]) in muscle of (A) lake trout, and (B) burbot from lakes in Wrangell-St. Elias National Park 

and Preserve, Alaska................................................................................................................................................... 14

Figure 8. Modeled relationship between fish size and the percentage of Arctic grayling, burbot, and

lake trout from Tanada Lake, Wrangell-St. Elias National Park and Preserve, Alaska, that exceed 

defined toxicological benchmarks for fishes, avian, and human consumers................................................................ 16

Tables

Table 1. Site locations and sample information for sites sampled in Wrangell-St. Elias National Park and Preserve, 

Alaska ............................................................................................................................................................................ 4

Table 2. Comparison of coefficient of determination (R2) and P-values between mercury-age and mercury-length 

regressions from fish sampled in Wrangell-St. Elias National Park and Preserve, Alaska ............................................ 9

Table 3. Percentage of fish from four lakes in Wrangell-St. Elias National Park and Preserve, Alaska, with 

raw (that is, non-size corrected) total mercury concentrations exceeding defined toxicity benchmarks for fish, 

avian, and human risk.................................................................................................................................................. 15
v 

Conversion Factors and Datum

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

acre 0.0015625 square mile (mi2) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

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

°F = (1.8×°C)+32. 

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Elevation, as used in this report, refers to distance above the vertical datum.
vi

Abbreviations and Acronyms

AIC Akaike’s Information Criterion

AK-DHSS Alaska Department of Health and Social Services

ANCOVA Analysis of Covariance

dw dry weight

EPA U.S. Environmental Protection Agency

Hg mercury

LOER lowest-observed-effects-residue

MeHg methylmercury

n sample size

NOER no-observed-effects-residue

R2 coefficient of determination

RSD percent relative standard deviation

SE standard error

THg total mercury

WRST Wrangell-St. Elias National Park and Preserve

ww wet weight

yr year or years
1 

Mercury in Fishes from Wrangell-St. Elias National Park 

and Preserve, Alaska

By Brandon M. Kowalski, James J. Willacker, Jr., Christian E. Zimmerman, and Collin A. Eagles-Smith

Abstract

In this study, mercury (Hg) concentrations were examined in fishes from Wrangell-St. Elias 

National Park and Preserve, Alaska, the largest and one of the most remote units in the national park 

system. The goals of the study were to (1) examine the distribution of Hg in select lakes of Wrangell-St. 

Elias National Park and Preserve; (2) evaluate the differences in Hg concentrations among fish species 

and with fish age and size; and (3) assess the potential ecological risks of Hg to park fishes, wildlife, 

and human consumers by comparing Hg concentrations to a series of risk benchmarks. Total Hg 

concentrations ranged from 17.9 to 616.4 nanograms per gram wet weight (ng/g ww), with a mean (± 

standard error) of 180.0 ±17.9 across the 83 individuals sampled. Without accounting for the effects of 

size, Hg concentrations varied by a factor of 10.9 across sites and species. After accounting for the 

effects of size, Hg concentrations were even more variable, differing by a factor of as much as 13.2 

within a single species sampled from two lakes. Such inter-site variation suggests that site 

characteristics play an important role in determining fish Hg concentrations and that more intensive 

sampling may be necessary to adequately characterize Hg contamination in the park. Size-normalized 

Hg concentrations also differed among three species sampled from Tanada Lake, and Hg concentrations 

were strongly correlated with age. Furthermore, potential risks to park fish, wildlife, and human users 

were variable across lakes and species. Although no fish from two of the lakes studied (Grizzly Lake 

and Summit Lake) had Hg concentrations exceeding any of the benchmarks used, concentrations in 

Copper Lake and Tanada Lake exceeded conservative benchmarks for bird (90 ng/g ww in whole-body) 

and human (150 ng/g ww in muscle) consumption. In Tanada Lake, concentrations in most fishes also 

exceeded benchmarks for risk to moderate- and low-sensitivity avian consumers (180 and 270 ng/g ww 

in whole-body, respectively), as well as the concentration at which Alaska State guidelines suggest atrisk groups limit fish consumption to 3 meals per week (320 ng/g). However, the relationship between 

Hg concentrations and fish size in Tanada Lake suggests that consumption of smaller-sized fishes could 

reduce Hg exposure in human consumers. 

Introduction

Contamination of aquatic ecosystems with mercury (Hg) is a widespread threat, affecting fish 

and wildlife, and posing risks for humans that consume fish (Scheuhammer and others, 2007). 

Atmospheric deposition of anthropogenic Hg emitted from fossil fuel combustion is among the primary 

pathways into aquatic ecosystems, although there also are many natural sources (for example, volcanoes 

and forest fires) that contribute to global background of Hg contamination (Driscoll and others, 2013). 

Within aquatic ecosystems, natural processes convert inorganic Hg to methylmercury (MeHg), a form 

of Hg that biomagnifies in aquatic food webs (Lavoie and others, 2013) and is highly toxic to fish and 

wildlife (Evers and others, 2007; Scheuhammer and others, 2007; Schwindt and others, 2008). 
2 

The widespread distribution of atmospheric Hg places even remote environments at risk for Hg 

contamination. In particular, national parks in the United States often are remote and among the most 

protected public lands, yet are affected by anthropogenic Hg (Landers and others, 2008; Eagles-Smith 

and others, 2014). As a result, it is important to understand the extent and environmental consequences 

of Hg contamination in national parks. Moreover, Hg contamination has important implications for 

consumption of fish by subsistence users and park visitors who fish regularly in contaminated waters. 

Wrangell-St. Elias National Park and Preserve (WRST) is an Alaska National Interest Lands 

Conservation Act national park, and as such, it provides access to subsistence harvest for many rural 

residents. A recent study of Hg in fish from 21 western national parks documented that some of the 

highest Hg concentrations were measured in fish from WRST (Eagles-Smith and others, 2014), with 

geometric mean values exceeding health criteria for the protection of fish-eating birds, mammals, and 

humans. However, it is unclear whether elevated Hg concentrations in fish from WRST are due to 

biological characteristics of the fish sampled (that is, age, size, species, trophic status, etc.) compared to

local factors that enhance the availability of Hg within these food webs. Therefore, in order to better 

understand the distribution of Hg in WRST and the associated risk to aquatic communities and park 

visitors, Hg concentrations were measured in several fish species from four lakes in WRST, three of 

which were sampled previously by Eagles-Smith and others (2014). The primary objectives were to: 

1. Determine the distribution of Hg concentrations in fishes among four lakes in WRST; 

2. Evaluate the differences in fish Hg concentrations among fish species, and with fish age and 

size; and

3. Assess toxicological risk within the park by comparing Hg concentrations in fishes to a series of 

eight previously developed toxicological benchmarks for fish, fish-eating birds, and humans. 

Methods

Study Sites and Sample Collection 

Wrangell-St. Elias National Park and Preserve is the largest national park in the United States, 

spanning about 13.2 million acres and bounded on the south by the Gulf of Alaska coast (fig. 1). The 

park was established in 1980 and is managed to protect ecological integrity and heritage resources of 

south-central Alaska, while providing public use in a wild setting (Hood and others, 2006). The climate 

in the park is variable and extreme. Winter low temperatures can reach -40  ̊C and summer high 

temperatures can reach 33  ̊C (Sousanes, 2012). Wrangell-St. Elias National Park and Preserve contains 

more than 96,000 acres of lakes and ponds, and more than 20,000 km of flowing waters. The park is 

divided into six major watersheds—the Bremner River, Chitina River, Copper River, Nabesna River, 

and White River drainages—and coastal streams (Weeks, 2003). The Copper River is the major river in 

the region, and the Bremner and Chitina Rivers flow westward into it and ultimately to the Gulf of 

Alaska. In contrast, the Nebesna and White Rivers are part of the Yukon River watershed, which drains 

into the Bering Sea. 
3 

Figure 1. Schematic of four study lakes in Wrangell-St. Elias National Park and Preserve, Alaska. 
4 

This study focuses on fish collected from four lakes in WRST (fig. 1; table 1). Tanada Lake is a 

large (2,718 acres), deep (53 m) lake in the Copper River headwaters at an elevation of 880 m. Copper 

Lake, also is in the Copper River headwaters, 3 km west of Tanada Lake. Copper Lake has a surface 

area of 1,803 acres, with a maximum depth of 72 m, and is at an elevation of 886 m. Both Tanada lake 

and Copper lake contain burbot (Lota lota), lake trout (Salvelinus namaycush), Arctic grayling 

(Thymallus arcticus), round whitefish (Prosopium cylindraceum), longnose sucker (Catostomus 

catostomus), and sockeye salmon (Oncorhynchus nerka), which provide subsistence and recreational 

fishing opportunities (Weeks, 2003; Schwanke and McCormick, 2010; Kukkonen and Zimpelman, 

2012). Copper Lake also has non-anadromous kokanee (Oncorhynchus nerka). Much less information is 

available for Grizzly and Summit Lakes. Grizzly Lake is at an elevation of 1,110 m within the Nabesna 

River drainage, and has a surface area of 252 acres and a maximum depth of 10 m. Grizzly Lake is 

known to contain burbot and Arctic grayling. Summit Lake is about 130 km southwest of Tanada Lake 

at an elevation of 860 m in the Chitna River drainage of the Chugach Mountains, and contains 

introduced rainbow trout (Oncorhynchus mykiss). 

National Park Service and Alaska Department of Fish and Game personnel collected fish from 

each of these four lakes in 2013. Fish were sampled using hoop nets, fyke nets, and hook and line. Four 

species of fish—Arctic grayling, burbot, lake trout, and rainbow trout—were collected. However, not all 

species were collected at all sites (table 1). After collection, fish were euthanized, placed on ice, 

measured (total length), wrapped in aluminum foil, individually labeled, frozen, and shipped to the 

laboratory for Hg analysis. After arrival at the laboratory, fish were stored at -20° C until dissection and 

processing.

Table 1. Site locations and sample information for sites sampled in Wrangell-St. Elias National Park and 

Preserve, Alaska.

[SR: Size regression used—Y, yes; N, no]

Coordinates Standard length 

(millimeters)

Site and species Latitude Longitude Elevation(meters) Number Mean Range SR

Copper Lake 62.425 -143.555 886

lake trout 15 378 297-454 N

Grizzly Lake 62.222 -143.365 1110

burbot 15 563 505-615 N

Summit Lake 61.315 -144.191 860

rainbow trout 15 309 200-388 N

Tanada Lake 62.425 -143.371 880

Arctic grayling 10 301 250-355 Y

burbot 13 483 345-565 Y

lake trout 15 413 330-470 Y
5 

Sample Preparation

In the laboratory, we thawed fish at room temperature and then measured standard length (SL) to 

the nearest millimeter on a fish board, and mass to the nearest gram with a digital hand-held fish scale.

Equations for converting standard length to total length for each species are provided in appendix 1. We 

excised 5–10 g of skinless axial muscle just anterior to the dorsal fin using acid-rinsed stainless-steel

scalpels. After removal, muscle tissue was rinsed with deionized water, blotted dry with a lint-free wipe, 

and weighed to the nearest 0.0001 g. The muscle tissue was then placed onto a clean aluminum weigh 

pan and dried in a convection oven at 50° C until a constant mass was achieved (typically 48 hours). 

Once dried, samples were stored in a desiccator until they cooled to room temperature. Finally, the dried 

muscle samples were weighed to the nearest 0.0001 g and ground to a fine powder using a ceramic 

mortar and pestle. Each mortar and pestle was rinsed with deionized water, dilute HCl, and deionized 

water again between samples to avoid cross contamination 

Otolith Removal and Preparation

Left and right sagittal otoliths were removed from each fish in order to estimate fish age. The 

shape and size of the otoliths varied among species; therefore, we used one of three otolith preparation 

methods depending on species. Rainbow trout otoliths were mounted flat, with the sulcus facing up on a 

clear glass microscope slide using cyanoacrylate adhesive. Excess otolith material was removed using 

400- and (or) 600-μm grit wet/dry sandpaper followed by polishing with a sequence of progressively 

finer lapping paper ranging from 30 μm to 1 μm. Burbot otoliths were prepared using a “break and 

burn” method (Panfili and others, 2002; Committee of Age-Reading Experts, 2006) because they are 

very large and were difficult to polish using whole-otolith mounting methods. Briefly, burbot otoliths 

first were scored in the center using a scalpel, cracked in half, burned using a butane lighter, and 

polished using the sequential sanding-polishing methods described above. Finally, lake trout and Arctic 

grayling otoliths were mounted in thermoplastic cement (CrystalbondTM 509, Ted Pella, Inc.), sectioned, 

and polished following the methods outlined in Black and others (2013) at the U.S. Geological Survey

Alaska Science Center. In all cases, polishing was considered complete when the growth increments 

were clearly visible from the margins to the nucleus, and age was estimated by counting the sequence of 

transparent and opaque annuli along the plane from the nucleus to the margin. Age estimates were 

determined independently by two individual readers, and any discrepancies were resolved using a third 

independent estimate.

Mercury Determination

Total Hg (THg) concentrations were determined in dried axial muscle following U.S. 

Environmental Protection Agency (EPA) method 7473 (2000) on a Milestone tri-cell DMA-80 Direct 

Mercury Analyzer® (Milestone Inc., Monroe, Connecticut). Total Hg concentration is an accepted proxy 

for MeHg concentrations because nearly all Hg in fish muscle is in the MeHg form (Hall and others, 

1997). Quality-assurance measures included analysis of three certified reference materials (DORM4, 

TORT2, or DOLT4; National Research Council of Canada, Ottawa, Canada), two system and method 

blanks, and two duplicates per batch of 30 samples. Recoveries (± standard error [SE]) averaged 97.5 

±2.4 percent (n=11) and 101.5 ±2.8 percent (n=10) for certified reference materials and calibration 

checks, respectively. Absolute relative percent differences (RSD) for all duplicates averaged 2.3 ±0.7 

percent (n=11).
6 

Statistical Analyses

We conducted all statistical analyses of Hg concentrations on a dry weight (dw) basis in order to 

control for variability in tissue moisture. However, we also calculated wet weight (ww) concentrations 

using individual-based moisture content and present the data in wet weight to facilitate comparisons 

with other studies. Moisture content in the fish muscle ranged from 65.1 to 81.4 percent with a mean 

(±SE) of 76.6 ±0.4 percent. 

Because fish size is often correlated with THg concentrations (Wiener and Spry, 1996), we first 

evaluated site- and species-specific length compared to THg relationships. Where appropriate, we sizenormalized THg concentrations of each fish to facilitate comparisons across sites and species. To make 

this determination, we evaluated the strength of each relationship based on their coefficient of 

determination (R2) and Akaike’s Information Criterion (AIC) for size compared to THg concentration 

(log10-transformed) regression models from each species-site combination. No size normalization was 

conducted for models with R2 less than 0.2. For regression models with R2 greater than 0.2, AIC values 

were compared between the regression model and a null model. If the size by THg model had an AIC 

value of 2 units or lower (indicating a meaningful difference in model fit; Burnham and Anderson, 

2010), size adjustments were made. We determined the sizes at which THg concentrations were 

normalized based on the size distribution of fish in each sample and the comparisons being made (see 

below). Mercury concentrations were size-normalized to median fish lengths by extracting the site- and 

species-specific regression model coefficients, and adding the individual residuals to the normalized 

predicted value.

Because we could not directly compare samples across all species and sites due to differences in 

species collected from each lake, we used a tiered statistical design to assess differences in THg 

concentrations among species within a lake, as well as among lakes for select species. For the withinlake assessment, Analysis of Covariance (ANCOVA) was used to compare size-normalized (350 mm 

SL) THg concentrations in Arctic grayling, burbot, and lake trout from Tanada Lake. In order to account 

for the effects of variable moisture content in the fish while facilitating intuitive interpretation, we 

converted the normalized THg concentrations (derived using dry weight data) to wet weight 

concentrations using percent moisture values for each fish and then included percent moisture in the 

ANCOVA model as a covariate. Thus, statistical results are presented on a wet weight basis, but 

adjusted for variable moisture content. 

Because burbot and lake trout were both collected from more than one lake, ANCOVA was used 

to examine inter-lake variation in THg concentrations of burbot (from Grizzly and Tanada Lakes) and 

lake trout (from Copper and Tanada Lakes). Neither burbot from Grizzly Lake nor lake trout from 

Copper Lake had significant relationships between standard length and THg concentration that 

necessitated size adjustments of THg concentrations as described above. Conversely, THg increased 

with increasing standard length in both species from Tanada Lake. Therefore, burbot and lake trout from 

Tanada Lake were normalized to the median length of the species in Grizzly Lake (burbot, 550 mm SL) 

and Copper Lake (lake trout, 378 mm SL). Variation in moisture contents of individuals were accounted 

for by including percent moisture as a covariate in the ANCOVA model as described above. 
7 

Toxicological Risk Estimation

In addition to comparing THg concentrations among lakes and species, we also evaluated the 

potential ecological risk of Hg exposure to fish, fish-eating birds, and humans by comparing THg 

concentrations to a series of eight previously developed toxicological benchmarks. Mercury 

concentrations in muscle were converted to whole-body concentrations (Peterson and others, 2005) in 

order to assess the toxicological risks of Hg to wildlife and fish, whereas muscle Hg concentrations 

were used to assess the toxicological risks to humans. 

To assess potential toxicological effects of Hg to fish, we compared estimates of whole-body 

THg concentrations to a no-observed-effects-residue (NOER) of 200 ng/g ww (Beckvar and others, 

2005) and a lowest-observed-effects-residue (LOER) of 300 ng/g ww (Sandheinrich and others, 2011). 

Tissue THg concentrations less than the NOER benchmark are not commonly associated with altered 

behavioral, development, growth, or reproduction of fishes, whereas THg concentrations in fishes 

greater than the LOER benchmark have been consistently associated with sublethal effects of Hg, 

including changes in reproductive health (Sandheinrich and others, 2011). For fish-eating birds, wholebody THg concentrations were compared to three toxicological benchmarks representing risks to highly 

sensitive, moderately sensitive, and relatively insensitive species. Because robust estimates of dietary 

thresholds exist for only a few species, we used the threshold derived for a well-studied, moderately 

sensitive species, the common loon (Gavia immer; Scheuhammer and others, 2007; Kenow and others, 

2008; Mitro and others, 2008; Scheuhammer and others, 2008; Heinz and others, 2009; Kenow and 

others, 2011), as a baseline. A review of field and laboratory studies on Hg toxicity in common loons 

found that Hg concentrations greater than 180 ng/g ww in prey fish were associated with significant 

reductions in reproductive success of wild loons (Depew and others, 2012). We used this concentration 

as the benchmark for risk to moderately sensitive avian consumers, and evaluated the likely range of 

risk to more-or-less-sensitive avian consumers by scaling this threshold by ±50 percent. Thus, risk to 

avian consumers was assessed by comparing Hg concentrations in whole-body fish to 90 (high 

sensitivity), 180 (moderate sensitivity), and 270 ng/g ww (low sensitivity) benchmarks. For human 

health risk, muscle THg concentrations were compared to three fish consumption guidelines 

recommended by the Alaska Department of Health and Social Services (AK-DHSS) to protect women 

who are or can become pregnant, nursing mothers, and young children (aged 12 years or younger; 

Verbrugge, 2007). These guidelines (150, 320, and 640 ng/g ww in fish muscle) correspond to the 

concentrations at which AK-DHSS recommends at-risk groups limit fish consumption to 4, 3, and 1 

meal per week, respectively, and aim to balance the risks and health benefits of fish consumption. 
8 

Comparisons were made to these benchmarks using two approaches. First, we compared raw 

(that is, not size-normalized), whole-body (fish and avian benchmarks) or muscle (human benchmarks) 

THg concentrations to each of the eight benchmarks and enumerated the proportion of individuals of 

each species in each lake that exceeded the benchmarks. This approach provides a coarse overview of 

risk for each species and site, but does not account for the effects of fish size on risk in those 

populations with size-THg relationships. Therefore, the second approach assessed the proportion of 

individuals that would exceed each benchmark over the range of standard lengths observed in the 

sample. To accomplish this comparison, site- and species-specific length-THg relationships were used 

to model risk at 1-mm size increments over the entire range of lengths observed in the sample.

Effectively, all fish in a sample were normalized to the size of the smallest fish, then in 1-mm

increments until the size of the largest fish in a sample was reached. At each of these size increments, 

the proportion of fish exceeding each benchmark was enumerated. Uncertainty in these size-specific risk 

estimates was preserved by comparing the bounds of a 95-percent prediction interval for each fitted 

value to the benchmarks. Thus, the resulting graphics show the estimated proportion of fish in a 

population that would exceed a threshold at a given size and can be used to identify the size of fish at 

which some threshold of acceptable risk is exceeded. 

Results

We analyzed THg concentrations in a total of 83 fish from the four study lakes in 2013—15 lake 

trout from Copper Lake, 15 burbot from Grizzly Lake, and 15 rainbow trout from Summit Lake, as well 

as 15 lake trout, 10 Arctic grayling, and 13 burbot from Tanada Lake. Total Hg concentrations ranged 

from 17.9 to 616.4 ng/g ww across all sites and species, with a mean (±SE) THg concentration of 180.0 

±17.9 ng/g ww. Site- and species-specific mean THg concentrations were highest in burbot (382.5 ±40.3 

ng/g ww) and lake trout from Tanada Lake (371.7 ±26.8 ng/g ww), followed by lake trout from Copper 

Lake (144.7 ± 6.7 ng/g ww), Arctic grayling from Tanada Lake (108.6 ±9.2 ng/g ww), burbot from 

Grizzly Lake (40.6 ± 4.4 ng/g ww), and rainbow trout from Summit Lake (35.2 ±3.3 ng/g ww; fig. 2). 

However, THg concentrations were correlated with fish size in some populations (fig. 3), necessitating 

size-adjustment of THg concentrations in order to make accurate comparisons. Similarly, some, but not 

all, populations had significant positive relationships between age and THg concentration (fig. 4). Age 

generally was a better predictor of fish THg concentrations than length (table 2). Total Hg

concentrations in Tanada Lake Arctic grayling (R2

=0.55, P=0.0042) and lake trout (R2=0.72, P<0.0001) 

were correlated with age, whereas burbot from Tanada (R2 = 0.37, P = 0.0230) and Grizzly Lakes 

(R2

=0.31, P=0.0247) had weaker correlations. There was no relationship between age and THg 

concentration in lake trout from Copper Lake (R2

=-0.01, P=0.4354) or rainbow trout from Summit Lake 

(R2=-0.05, P=0.5449). Length by age plots indicated that fish size in several populations approached an 

asymptote of maximum size in the oldest individuals (fig. 5).
9 

Figure 2. Arithmetic-mean total mercury concentrations (THg, in nanograms per gram wet weight [ng/g ww]) ±1

standard error in fish species collected from four lakes in Wrangell-St. Elias National Park and Preserve, Alaska. 

Table 2. Comparison of coefficient of determination (R2) and P-values between mercury-age and mercury-length 

regressions from fish sampled in Wrangell-St. Elias National Park and Preserve, Alaska.

Site and species

Age Size

R2 P-value R2 P-value

Copper Lake

lake trout -0.01 0.4354 -0.08 0.9412

Grizzly Lake

burbot 0.31 0.0247 0.11 0.1218

Summit Lake

rainbow trout -0.05 0.5449 0.04 0.2384

Tanada Lake

Arctic grayling 0.55 0.0042 0.36 0.0388

burbot 0.37 0.0230 0.34 0.0216

lake trout 0.72 <0.0001 0.39 0.0077
10

Figure 3. Linear relationships between standard length (in millimeters, [mm]) and total mercury concentrations 

(THg, in nanograms per gram dry weight [ng/g dw]) in fish muscle of (A) Arctic grayling, (B) burbot, (C) lake trout, 

and (D) rainbow trout sampled from Wrangell-St. Elias National Park and Preserve, Alaska. 
11

Figure 4. Linear relationships between fish age (in years) and total mercury concentrations (THg, in nanograms 

per gram dry weight [ng/g dw]) in fish muscle of (A) Arctic grayling, (B) burbot, (C) lake trout, and (D) rainbow trout 

sampled from Wrangell-St. Elias National Park and Preserve, Alaska. 
12

Figure 5. Logarithmic relationships between fish age (in years) and standard length (in millimeters [mm]) of (A) 

Arctic grayling, (B) burbot, (C) lake trout, and (D) rainbow trout sampled from Wrangle-St. Elias National Park and 

Preserve, Alaska. 
13

Species Comparisons

Tanada Lake was the only site from which more than one species was collected; therefore, 

species comparisons were limited to Tanada Lake. After size -normalizing THg concentrations in all 

fish from Tanada Lake to 350 mm SL, we found significant differences in the THg concentrations 

among the species (fig. 6; F2,37=10.08, P=0.0004). Concentrations were highest in lake trout (253.2 

±24.6 ng/g ww), and lowest in Arctic grayling (133.2 ±13.5 ng/g ww). Burbot THg concentrations were 

intermediate (184.6 ±19.0 ng/g ww) between the other two species, but were not statistically different 

from either lake trout (P=0.15) or grayling (P=0.08). 

Figure 6. Back-transformed least-square mean total mercury concentrations (THg, in nanograms per gram wet 

weight [ng/g ww]) in muscle of fishes from Tanada Lake, Wrangell-St. Elias National Park and Preserve, Alaska. All 

concentrations are size-normalized to 350 millimeters standard length and error bars are standard errors estimated 

using the delta method.
14

Site Comparisons

We observed inter-lake differences in the THg concentrations of lake trout and burbot that were 

each sampled from two lakes (burbot, F1,27=112.82, P <0.0001; lake trout, F1,29=31.93, P <0.0001; fig. 

7). Size-normalized (550 mm SL) THg concentrations in burbot were higher in Tanada Lake (535.2 

±34.7 ng/g ww) than in Grizzly Lake (40.6 ± 31.1 ng/g ww), despite similar median ages in the two 

populations (Tanada Lake=12 yr; Grizzly Lake=10 yr; fig. 5). Likewise, size-normalized (378 mm SL) 

THg concentrations in lake trout were higher in Tanada Lake (302.9 ±14.4 ng/g ww) than in Copper 

Lake (138.7 ±25.2 ng/g ww), even though the median age of both populations was 13 yr (fig. 5). 

Figure 7. Back-transformed least-square mean total mercury concentrations (THg, in nanograms per gram wet 

weight [ng/g ww]) in muscle of (A) lake trout, and (B) burbot from lakes in Wrangell-St. Elias National Park and 

Preserve, Alaska. Lake trout from Tanada Lake were size-normalized to the median length of Copper Lake lake 

trout (378 millimeters). Burbot from Tanada Lake were size-normalized to the median length of Grizzly Lake burbot 

(550 millimeters). Mercury concentrations for lake trout from Copper Lake and burbot from Grizzly Lake are 

geometric means. Error bars are standard errors estimated using the delta method.
15

Toxicological Risks 

Fish Risk

We first assessed risk to fishes based on the proportion of non-size-normalized, whole-body THg 

concentrations that exceeded the selected toxicological benchmarks. Across all sites and species, 24 percent 

of fish sampled (20 individuals) had whole-body THg concentrations exceeding the NOER benchmark for 

which Hg exposure may affect fish health (200 ng/g ww; table 3), and 6 percent (5 individuals) had 

concentrations exceeding the LOER benchmark (300 ng/g ww; table 3). All fish exceeding the NOER

benchmark were from Tanada Lake, where 53 percent of the fish sampled (20 individuals) exceeded the 

benchmark. On a species specific-basis, in Tanada Lake, none of the Arctic grayling, 62 percent of the 

burbot (8 individuals), and 80 percent of the lake trout (12 individuals) exceeded the 200 ng/g NOER 

benchmark. Across all species, 13 percent of fish (5 individuals) from Tanada Lake exceeded the LOER 

benchmark, comprised of 23 percent of burbot (3 individuals) and 13 percent of lake trout (2 individuals), 

and no Arctic grayling. 

Table 3. Percentage of fish from four lakes in Wrangell-St. Elias National Park and Preserve, Alaska, with raw 

(that is, non-size corrected) total mercury concentrations exceeding defined toxicity benchmarks for fish, avian, and 

human risk. 

[Fish and avian benchmarks are based on wet weight whole-body concentrations whereas human benchmarks are based on 

wet weight concentrations in fish muscle] 

Fish toxicity Bird toxicity Human consumptionc

Site and species NOERa 

(200 ng/g)

LOERb 

(300 

ng/g)

High

sensitivityy

(90 ng/g)

Mod.

sensitivity.

(180 

ng/g)

Low

sensitivity.

(270 

ng/g)

Unrestricted 

consumption

(150 ng/g)

4 Meals 

per 

week

(320 

ng/g)

2 Meal 

per week

(640 

ng/g)

Across All Sites 24 6 45 25 7 41 25 --

Copper Lake

lake trout -- -- 53 -- -- 40 -- --

Grizzly Lake

burbot -- -- -- -- -- -- -- --

Summit Lake

rainbow trout -- -- -- -- -- -- -- --

Tanada Lake 53 13 76 55 16 74 55 --

Arctic grayling -- -- 20 -- -- 10 -- --

burbot 62 23 92 69 31 92 62 --

lake trout 80 13 100 80 13 100 87 --

a

No-Observed-Effects-Residue (Beckvar and others, 2005).

b

Lowest-Observed-Effects-Residue (Sandheinrich and others, 2011).

c

Based on Alaska-caught fish monthly consumption allowances for women who are or can become pregnant, nursing mothers, 

and young children (aged 12 years and under).
16

We also examined risk over the size range of fish sampled in order to account for the effects of 

size and age on THg concentrations. These size-specific risk models predicted that Arctic grayling 

would not exceed the 200 ng/g ww NOER or the 300 ng/g ww LOER benchmarks at any size sampled 

(fig. 8). Conversely, burbot and lake trout were predicted to first exceed the NOER toxicological 

benchmark at 370 and 356 mm SL, respectively, with greater than or equal to 50 percent of each 

population expected to exceed this threshold at 492 and 398 mm SL. One-hundred percent of burbot and 

lake trout with greater than 559 and 470 mm SL, respectively, were predicted to exceed the NOER 

(appendix 2). Burbot and lake trout first exceeded the LOER benchmark at 463 and 432 mm SL, 

respectively, and both plateaued at about 46 percent of the population exceeding the benchmark at 565 

and 470 mm SL, respectively (fig. 8).

Figure 8. Modeled relationship between fish size and the percentage of Arctic grayling, burbot, and lake trout

from Tanada Lake, Wrangell-St. Elias National Park and Preserve, Alaska, that exceed defined toxicological 

benchmarks for fishes, avian, and human consumers. Fishes: Percentage of whole-body total mercury 

concentrations at the sampled size range that exceed benchmarks for a generic no-observed-effects residue 

(green; 200 ng/g ww), and lowest-observed-effects residue (red; 300 nanograms per gram wet weight [ng/g ww]) 

for fish health. Avian: Percentage of whole-body total mercury concentrations at the sampled size range that 

exceed dietary toxicity benchmarks for piscivorous birds that can be classified as high (green; 90 ng/g ww), 

medium (orange; 180 ng/g ww), or low (red; 270 ng/g ww) sensitivity. Human: Percentage of muscle total mercury 

concentrations exceeding the Alaska Department of Health and Social Services guidelines at which they 

recommend women of childbearing age and children younger than 12 years of age consume no more than 4 meals 

per week (green; 150 ng/g ww), 3 meals per week (orange; 320 ng/g ww), or 2 meals per week (red; 640 ng/g ww).
17

Avian Risk

Across all sites, 45 percent of fish sampled (37 individuals) had THg concentrations greater than 

the proximate benchmark for Hg effects to highly sensitive avian piscivores (90 ng/g ww), 25 percent 

(21 individuals) had tissue concentrations greater than the benchmark for moderate-sensitivity species 

(180 ng/g ww), and 7 percent (6 individuals) had concentrations greater than the benchmark for lowsensitivity species (270 ng/g ww; table 3). Whole-body THg concentrations exceeded the highsensitivity benchmark in lake trout from Copper Lake (53 percent [8 individuals] of fish) and in all three 

fish species from Tanada Lake (Arctic grayling—20 percent [2 individuals]; burbot—92 percent [12 

individuals]; lake trout—100 percent [15 individuals]). Only burbot and lake trout from Tanada Lake 

exceeded the moderate-sensitivity benchmark (69 and 80 percent [9 and 12 individuals] for burbot and 

lake trout, respectively) and low-sensitivity benchmark (31 and 13 percent [4 and 2 individuals], 

respectively; table 3). 

Size-specific risk models estimated that whole-body THg concentrations exceeded the highsensitivity benchmark for all three species in Tanada Lake (fig. 8). Arctic grayling first exceeded the 

high-sensitivity benchmark at 308 mm SL, with greater than or equal to 50 percent of the population 

expected to exceed this benchmark at 336 mm SL (appendix 2). Seventy-six percent of burbot exceeded 

the high-sensitivity benchmark at 345 mm SL, the lowest length observed for this species in Tanada 

Lake. One hundred percent of the burbot exceeded the high-sensitivity avian benchmark at 377 mm SL, 

and all lake trout exceeded this benchmark at the lowest observed length of 330 mm. None of the Arctic 

grayling were modeled to exceed the moderate- or low-sensitivity benchmarks within the size range 

sampled. Burbot first exceeded the moderate-sensitivity benchmark at 346 mm SL, greater than or equal 

to 50 percent of the population exceeded at 468 mm SL, and 100 percent at 535 mm SL. Lake trout from 

Tanada Lake were first modeled to exceed the moderate-sensitivity benchmark at 337 mm SL, with 

greater than or equal to 50 percent and 100 percent exceeding this threshold at 378 and 450 mm SL, 

respectively. Burbot and lake trout first exceeded the low-sensitivity benchmark at 439 and 413 mm SL, 

respectively. Greater than 50 percent of burbot and lake trout whole-body THg concentrations exceeded 

the low sensitivity threshold at 561 and 454 mm SL, respectively (appendix 2).

Human Consumption Risk 

For the raw, unadjusted data across all sites, 41 percent of the fish sampled (34 individuals) had 

THg concentrations in their muscle that exceeded the AK-DHSS unrestricted human consumption 

guideline (150 ng/g ww in fish muscle), 25 percent of the fish sampled (21 individuals) exceeded the 4-

meal-per-week AK-DHSS guideline (320 ng/g ww), and none of the fish had concentrations greater 

than the guideline at which AK-DHSS recommends consumption be limited to 1 meal per week. Forty

percent of lake trout (6 individuals) from Copper Lake exceeded the unrestricted consumption guidance 

benchmark, although no fish from Copper Lake were determined to have muscle THg concentrations 

greater than the 4-meal-per-week guideline. Ten percent of Arctic grayling (1 individual) from Tanada 

Lake exceeded the AK-DHSS unrestricted consumption guideline, whereas none exceeded the 4-mealper-week guideline. All lake trout and 92 percent of burbot (12 individuals) from Tanada Lake exceeded 

the unrestricted consumption guideline, whereas 87 percent of lake trout (13 individuals) and 62 percent 

of burbot (8 individuals) exceeded the 4-meal-per-week guideline. 
18

Total mercury muscle concentrations in fish sampled from Tanada Lake were modeled across 

the observed size range to assess the risks of human consumption (fig. 8). Arctic grayling were first 

modeled to exceed the AK-DHSS unrestricted consumption guideline at 315 mm SL, but no individuals 

were modeled to exceed the 4- or 2-meal-per week-guidelines at any size sampled. Fifty-four and 93 

percent of burbot and lake trout, respectively, exceeded the AK-DHSS unrestricted consumption 

guideline at the smallest sizes observed (345 and 330 mm SL, respectively; appendix 2). Models 

estimated that burbot and lake trout would first exceed the AK-DHSS 4-meal-per-week guideline at 365 

and 348 mm SL, respectively, and that 50 percent or more fish exceeded this benchmark at 484 and 391 

mm SL, respectively. One-hundred percent of burbot greater than 546 mm SL and lake trout greater 

than 459 mm SL were modeled to exceed the AK-DHSS 4-meal-per-week guideline. Some of the 

burbot greater than 503 mm SL and lake trout greater than 461 mm SL were modeled to exceed the AKDHSS 2-meal-per-week guideline, although they were never more than 30 percent of the population 

(fig. 8; appendix 2). 

Discussion

Results of this study indicate that Hg bioaccumulation and risk to remote aquatic ecosystems 

within WRST are highly variable among lakes and among species within a lake. Total Hg 

concentrations in individual fish ranged by an order of magnitude across the 83 individuals analyzed, 

with the highest concentrations exceeding 600 ng/g ww. Even within a single species, size-normalized 

THg concentrations differed among lakes. THg concentrations in lake trout from Tanada Lake were 2.2 

times higher than lake trout from Copper Lake, and concentrations in burbot from Tanada Lake were 

13.2 times higher than burbot from Grizzly Lake. Furthermore, some of the THg concentrations in fish, 

particularly from Tanada Lake, were high enough to be of concern for wildlife and humans that 

consume them. However, the relationship between THg concentrations and fish size in Tanada Lake 

suggests that Hg exposure in human consumers could be reduced by harvesting small-sized fishes. 

Although fish THg concentrations varied substantially among sites, they generally are 

comparable to those measured in these species from other studies in remote northern habitats. For 

example, THg concentrations in lake trout and Arctic grayling averaged between 58 and 216 ng/g ww, 

and 54 to 112 ng/g ww, respectively, in four lakes in Arctic Alaska (Allen-Gil and others, 1997). These 

concentrations are similar to those that we measured in fish from Copper, Grizzly, and Summit Lakes, 

but are considerably less than the mean values from Tanada Lake. Similarly, mean Hg concentrations 

for lake trout (180 ng/g ww) and burbot (150 ng/g ww) from Great Slave Lake, Canada (Evans and 

others, 2013) were comparable to those that we measured in Copper and Grizzly Lakes, but are 

considerably less than the mean values from Tanada Lake. It is unclear why THg concentrations in fish 

from Tanada Lake were elevated in comparison to the other lakes, but could be related to lake or 

catchment characteristics that facilitate higher bioaccumulation or biomagnification of Hg in this 

system, or to marine-derived sources associated with the return of anadromous fish since only Tanada 

Lake has substantial salmon returns each year (Written Communication, Dave Sarafin, National Park 

Service, 5/8/2014). Many factors are known to influence these processes, including Hg inputs, MeHg 

production, and food web processes that regulate the flow of Hg through systems. A primary source of 

Hg inputs into WRST lakes likely is atmospheric deposition (Jaffe and others, 2008; Durnford and 

others, 2010; Phillips and others, 2011). Despite the close proximity of three of the lakes assessed in this 

study, the surface area of Tanada Lake (2,718 acres) is 1.5 times greater than the surface area of Copper 

Lake (1,830 acres) and 11 times greater than the surface area of Grizzly Lake (252 acres). Additionally, 

the surface area of Tanada Lake catchment basin (84,830 acres) is 3 times greater than that of Copper 

Lake (26,804 acres), and 47 times greater than that of Grizzly Lake (1,790 acres). Therefore, even if the 
19

delivery rates per unit area are similar among the three lakes, the substantially larger lake and catchment 

size likely results in higher total atmospheric Hg loading in Tanada Lake relative to Copper Lake, and in 

Copper Lake relative to Grizzly Lake. Hg concentrations in fish follow these trends, suggesting that 

further investigation of the influence of catchment drivers is warranted. Differences in Hg 

concentrations among the four lakes also could reflect varying geologic conditions, such as differing 

bedrock composition or glacial activity in the upstream watersheds, a hypothesis that could be assessed 

by measuring Hg concentrations in sediment and water inputs to the lakes. 

Although Hg inputs play a role in determining Hg concentrations in fish, the biogeochemical 

factors that control MeHg production also are key drivers of Hg bioaccumulation in food webs (Ulrich 

and others, 2001; Benoit and others, 2003). Thus, lake and watershed characteristics, including the 

presence of wetlands, high-quality organic matter inputs, and low pH, facilitate Hg methylation and, 

thus, are often important drivers of Hg bioaccumulation in fish (Watras and others, 1998; Snodgrass and 

others, 2000; Greenfield and others, 2001; Wiener and others, 2006). In order to understand the role 

methylation plays in generating the variable THg concentrations measured in WRST fish, future 

research should include abiotic and low trophic-level sampling with the aim of identifying habitat, lake, 

and watershed characteristics that are associated with contamination in these parts of the ecosystems as 

well as higher trophic-level fishes. 

More than 90 percent of the MeHg exposure in fish comes from dietary sources (Hall and others, 

1997). Thus, differences in the feeding ecology strongly regulate the accumulation of Hg in tissues 

(Cabana and others, 1994; Vander Zanden and Rasmussen 1996; Power and others, 2002). The 

considerable variation in THg concentrations among the three species of fishes sampled from Tanada 

Lake suggests that variable bioavailability of MeHg is not the sole determinant of THg concentrations in 

these lakes. The two species with the highest THg concentrations (lake trout and burbot) are 

predominantly piscivorous as adults (Scott and Crossman, 1973; Mittlebach and Persson, 1998), and, 

therefore, occupy higher trophic positions, which results in higher levels of Hg biomagnification. In 

contrast, Arctic grayling tend to forage predominantly on benthic and emergent invertebrates 

(Armstrong, 1986). THg concentrations in invertivorous grayling were low compared to co-occurring 

piscivorous species in other areas of Alaska (Allen-Gil and others, 1997; Jewett and others, 2003) and 

throughout Canada (Lockhart and others, 2005). Although these data indicate that grayling from Tanada 

Lake typically are younger (median age=9.5 yr) than either burbot (12 yr) or lake trout (13 yr), THg 

concentrations in burbot and lake trout were consistently higher than in similarly aged grayling. Thus, it 

is unlikely that age alone could account for the observed variation. However, THg concentrations were 

more strongly correlated with age than size. This may indicate the relatively large size of the fish 

sampled and the asymptotic relationship between age and growth (Rao, 1958; Ricker, 1975), which 

could result in the decoupling of size-THg relationships once the asymptotic portion of the growth curve 

is reached. Because the point at which growth asymptotes varies among populations (Chen and others, 

1992; Murphy and Willis, 1996), populations may have differing relationships even when age or size 

structures are similar (for example, lake trout from Tanada Lake compared to Copper Lake in the 

current study). 
20

Although Hg exposure risk in WRST was not formally assessed, our data suggest that risk to 

park fish, wildlife, and humans is variable across lakes and species. Mercury concentrations in fishes 

from Grizzly Lake and Summit Lake did not exceed any of the guidelines used for comparisons, 

whereas concentrations in fishes from Copper Lake and Tanada Lake exceeded benchmarks for 

toxicological risk to fish, birds, and (or) humans (table 3). Despite the fact that only the most 

conservative benchmarks for bird (90 ng/g ww in whole body) and human (150 ng/g ww in muscle, 

corresponding to the AK-DHSS unrestricted consumption guideline) were exceeded in lake trout from 

Copper Lake, a relatively large percentage of individuals exceeded the human benchmark, suggesting 

that a more detailed evaluation of human consumption risk is warranted. Furthermore, THg 

concentrations in fishes from Tanada Lake regularly exceeded conservative benchmarks and 

benchmarks for risk to moderate- and low-sensitivity avian consumers (180 and 270 ng/g ww in whole 

body, respectively), as well as the AK-DHSS 4-meal-per-week guideline (320 ng/g ww in muscle). In 

particular, most of the burbot and lake trout from Tanada Lake exceeded these benchmarks (table 3).

This warrants further considerations because Tanada Lake is a known site of subsistence fisheries 

(Weeks, 2003; Schwanke and McCormick, 2010; Kukkonen and Zimpelman, 2012). However, our 

analyses suggest that selectively harvesting smaller individuals is one potential way to reduce human Hg 

exposure from Tanada Lake. For example, the model of risk as a function of fish size in Tanada Lake 

predicted that no burbot less than 365 mm SL or lake trout less than 348 mm SL were expected to 

exceed the AK-DHSS 4-meal-per-week guideline. Conversely, all burbot and lake trout with greater 

than 546 and 459 mm SL, respectively, exceeded this guideline. Such insights into the size at which risk 

thresholds are exceeded provide a valuable basis upon which managers can communicate and mitigate 

exposure risk to consumers. Nonetheless, the high degree of within-park variability suggests that size 

thresholds generated for one population may not reflect risk in other populations. Thus, follow-up 

research and monitoring efforts across sites within the park will be beneficial for adequately 

characterizing and determining future directions for minimizing risk to park fish, wildlife, and users. 

This study provides an important step towards understanding the distribution of Hg and potential 

risks posed to park wildlife and visitors. However, our study included only a small fraction of the 

aquatic resources and habitat types present within WRST. Such limited sampling is unlikely to 

adequately characterize Hg risk because of the substantial variation observed within other national parks 

(Eagles-Smith and others, 2014). Additional quantitative studies of the biogeochemical and food-web 

processes regulating inter-site and inter-species variation within the park will facilitate more accurate 

identification of the ecological risks associated with Hg. Finally, it is important that the toxicological 

effects of Hg on park fish and wildlife be directly assessed in order to develop risk benchmarks that 

reflect the species and habitats present in WRST, and, thus, more robustly portray risk to WRST 

ecosystems as a whole. 

Acknowledgments

This study was funded by Wrangell-St. Elias National Park and Preserve and the U.S. 

Geological Survey. This study would not have been possible without the facilitation of Molly 

McCormick at Wrangell-St. Elias National Park and Preserve and the efforts of the park staff that 

collected samples for analysis. We are grateful for the laboratory assistance provided by John Pierce, 

Jim Randolph, Austin Shick, and Mason Wagner, as well as database and mapping assistance from 

Branden Johnson. We thank Andrea Blakesley and Eric Veach for feedback on human risk guidelines, 

and Dave Sarafin, Angela Matz, Kyle Shedd, and Leah Kenney for providing thoughtful comments on 

previous versions of this report. 
21

References Cited

Allen-Gil, S., Gubala, C.P., Landers, D.H., Lasorsa, B.K., Crecelius, E.A., and Curtis, L.R., 1997, 

Heavy metal accumulation in sediment and freshwater fish in U.S. arctic lakes: Environmental 

Toxicology and Chemistry, v. 16, no. 4., p. 733–741. 

Armstrong, R.H., 1986, A review of Arctic grayling studies in Alaska: Biological Papers of University 

of Alaska, 1952–1982, no. 23, p. 3–17. 

Beckvar, N., Dillon, T.M., and Read, L.B., 2005, Approaches for linking whole-body fish tissue 

residues of mercury or DDT to biological effects thresholds: Environmental Toxicology and 

Chemistry, v. 24, no. 8, p. 2,094–2,105. 

Benoit, J.M., Gilmour, C.C., Heyes, A., Mason, R.P., and Miller, C.L., 2003, Geochemical and 

biological controls over methylmercury production and degradation in aquatic ecosystems, in Cai, 

Yong, and Braids, O.C., Biogeochemistry of environmentally important trace elements: American 

Chemical Society Symposium Series 835,, p. 262–297, doi:10.1021/bk-2003-0835.ch019. 

Black, B., von Biela, V., Zimmerman, C., and Brown, R., 2013, Lake trout otolith chronologies as 

multidecadal indicators of high-latitude freshwater ecosystems: Polar Biology, v. 36, no. 1, p. 147–

153. 

Burnham, K., and Anderson, D., 2010, Model selection and inference—A practical informationtheoretic approach: New York, Springer, 514 p. 

Cabana, G., and Rasmussen, J.B., 1994, Modeling food chain structure and contaminant 

bioaccumulation using stable nitrogen isotopes: Nature, v. 372, p. 255–257. 

Chen, Y., Jackson, D.A., and Harvey, H.H., 1992, A comparison of von Bertalanffy and polynomial 

functions in modelling fish growth data: Canadian Journal of Fisheries and Aquatic Sciences, v. 49, 

no. 6, p. 1,228–1,235. 

Committee of Age-Reading Experts, 2006, Manual on generalized age determination procedures for 

groundfish: Pacific States Marine Fisheries Commission, 52 p., 

http://care.psmfc.org/docs/CareManual2006.pdf . 

Depew, D.C., Basu, N., Burgess, N.M., Campbell, L.M., Evers, D.C., Grasman, K.A., and 

Scheuhammer, A.M., 2012, Derivation of screening benchmarks for dietary methylmercury exposure 

for the common loon (Gavia immer)—Rationale for use in ecological risk assessment: Environmental 

Toxicology and Chemistry, v. 31, no. 10, p. 2,399–2,407. 

Driscoll, C.T., Mason, R.P., Chan, H.M., Jacob, D.J., and Pirrone, N., 2013, Mercury as a global 

pollutant—Sources, pathways, and effects: Environmental Science and Technology, v. 47, no. 10, p. 

4,967–4,983. 

Durnford, D., Dastoor, A., Figueras-Nieto, D., and Ryjkov, A., 2010, Long range transport of mercury 

to the Arctic and across Canada: Atmospheric Chemistry and Physics, v. 10, no. 13, p. 6,063–6,086. 

Eagles-Smith, C.A., Willacker, J.J., Jr., and Flanagan Pritz, C.M., 2014, Mercury in fishes from 21 

national parks in the Western United States—Inter- and intra-park variation in concentrations and 

ecological risk: U.S. Geological Survey Open-File Report 2014-1051, 54 p. 

Evans, M., Muir, D., Brua, R.B., Keating, J., and Wang, X., 2013, Mercury trends in predatory fish in 

Great Slave Lake—The influence of temperature and other climate drivers: Environmental Science 

and Technology, v. 47, p. 12,793–12,801. 

Evers, D.C., Han, Y.J., Driscoll, C.T., Kamman, N.C., Goodale, M.W., Lambert, K.F., Holsen, T.M., 

Chen, C.Y., Clair, T.A., and Butler, T., 2007, Biological mercury hotspots in the northeastern United 

States and southeastern Canada: BioScience, v. 57, no. 1, p. 29–43. 
22

Greenfield, B.K., Hrabik, T.R., Harvey, C.J., and Carpenter, S.R., 2001, Predicting mercury levels in 

yellow perch—Use of water chemistry, trophic ecology, and spatial traits: Canadian Journal of 

Fisheries and Aquatic Sciences , v. 58, p. 1,419–1,429. 

Hall, B.D., Bodaly, R.A., Fudge, R.J.P., Rudd, J.W.M., and Rosenberg, D.M., 1997, Food as the 

dominant pathway of methylmercury uptake by fish: Water, Air, and Soil Pollution, v. 100, nos. 1–2, 

p. 13–24. 

Heinz, G.H., Hoffman, D.J., Klimstra, J.D., Stebbins, K.R., Kondrad, S.L., and Erwin, C.A., 2009, 

Species differences in the sensitivity of avian embryos to methylmercury: Archives of Environmental 

Contamination and Toxicology, v. 56, no. 1, p. 129–138. 

Hood, E., Eckert, G., Nagorski, S., and Talus, C., 2006, Assessment of coastal water resources and 

watershed conditions at Wrangell-St. Elias National Park and Preserve, Alaska: National Park Service 

Technical Report NPS/NRWRD/NRTR-2006-346, 77 p. 

Jaffe, D., and Strode, S., 2008, Sources, fate and transport of atmospheric mercury from Asia: 

Environmental chemistry, v. 5, no. 2, p. 121–126. 

Jewett, S.C., Zhang, X., Naidu, S., Kelley, A., Dasher, J., and Duffy, L.K., 2003, Comparison of 

mercury and methylmercury in northern pike and Arctic grayling from western Alaska rivers: 

Chemosphere, v. 50, no. 3, p. 383–392. 

Kenow, K.P., Hoffman, D.J., Hines, R.K., Meyer, M.W., Bickham, J.W., Matson, C.W., Stebbins, K.R., 

Montagna, P., and Elfessi, A., 2008, Effects of methylmercury exposure on glutathione metabolism, 

oxidative stress, and chromosomal damage in captive-reared common loon (Gavia immer) chicks: 

Environmental Pollution, v. 156, no. 3, p. 732–738. 

Kenow, K.P., Meyer, M.W., Rossmann, R., Gendron-Fitzpatrick, A., and Gray, B.R., 2011, Effects of 

injected methylmercury on the hatching of common loon (Gavia immer) eggs: Ecotoxicology, v. 20, 

no. 7, p. 1,684–1,693. 

Kukkonen, M., and Zimpelman, G., 2012, Subsistence harvests and uses of wild resources in 

Chistochina, Alaska, 2009: Anchorage, Alaska Department of Fish and Game, Division of 

Subsistence Technical Paper No. 370. 

Landers, D.H., Simonich, S.L., Jaffe, D.A., Geiser, L.H., Campbell, D.H., Schwindt, A.R., Schreck, 

C.B., Kent, M.L., Hafner, W.D., Taylor, H.E., Hagman, K.J., Usenko, S., Ackerman, L.K., Schrlau, 

J.E., Rose, N.L., Blett, T.F., and Erway, M.M., 2008, The fate, transport, and ecological impacts of 

airborne contaminants in western national parks (USA): U.S. Environmental Protection Agency 

Report EPA/600/R-07/138, Office of Research and Development, NHEERL, Western Ecology 

Division, Corvallis, Oregon. 

Lavoie, R.A., Jardine, T.D., Chumchal, M.M., Kidd, K.A., and Campbell, L.M., 2013, Biomagnification 

of mercury in aquatic food webs—A worldwide meta-analysis: Environmental Science and

Technology, v. 47, no. 23, p. 13,385–13,394. 

Lockhart, W.L., Stern, G.A., Low, G., Hendzel, M., Boila, G., Roach, P., Evans, M.S., Billneck, B.N., 

DeLaronde, J., Frieson, S., Kidd, K., Atkins, S., Muir, D.C.G., Stoddart, M., Stephens, G., 

Stephenson, S., Harbicht, S., Snowshoe, N., Grey, B., Thompson, S., and DeGraff, N., 2005, A 

history of total mercury in edible muscle of fish from lakes in northern Canada: Science of the Total 

Environment, v. 351, p. 427–463. 

Mitro, M.G., Evers, D.C., Meyer, M.W., and Piper, W.H., 2008, Common loon survival rates and 

mercury in New England and Wisconsin: Journal of Wildlife Management, v. 72, no. 3, p. 665–673. 

Mittelbach, G.G., and Persson, L., 1998, The ontogeny of piscivory and its ecological consequences: 

Canadian Journal of Fisheries and Aquatic Sciences, v. 55, no. 6, p. 1,454–1,465. 
23

Murphy, B.R., and Willis, D.W., eds., 1996, Fisheries techniques, 2nd edition: American Fisheries 

Society, 732 p. 

Panfili, J., De Pontual, H., Troadec, H., and Wright, P., 2002, Manual of fish sclerochronology: Brest, 

France, Ifremer-IRD coedition, 464 p. 

Peterson, S., Van Sickle, J., Hughes, R., Schacher, J., and Echols, S., 2005, A biopsy procedure for 

determining filet and predicting whole-fish mercury concentration: Archives of Environmental 

Contamination and Toxicology, v. 48, no. 1, p. 99–107. 

Phillips, V.J., St Louis, V.L., Cooke, C.A., Vinebrooke, R.D., and Hobbs, W.O., 2011, Increased 

mercury loadings to western Canadian alpine lakes over the past 150 years: Environmental Science 

and Technology, v. 45, no. 6, p. 2,042–2,047. 

Power, M., Klein, G.M., Guiguer, K.R.R.A., and Kwan, M.K.H., 2002, Mercury accumulation in the 

fish community of a sub-Arctic lake relation to trophic position and carbon sources: Journal of 

Applied Ecology, v. 39, no. 5, p. 819–830. 

Rao, C.R., 1958, Some statistical methods for comparison of growth curves: Biometrics, v. 14, p. 1–17. 

Ricker, W.E., 1975, Computation and interpretation of biological statistics of fish populations: Fisheries

Research Board of Canada, Bulletin 191, 382 p. 

Sandheinrich, M.B., Bhavsar, S.P., Bodaly, R.A., Drevnick, P.E., and Paul, E.A., 2011, Ecological risk 

of methylmercury to piscivorous fish of the Great Lakes region: Ecotoxicology, v. 20, no. 7, p. 1,577–

1,587. 

Scheuhammer, A.M., Basu, N., Burgess, N.M., Elliott, J.E., Campbell, G.D., Wayland, M., Champoux, 

L., and Rodrigue, J., 2008, Relationships among mercury, selenium, and neurochemical parameters in 

common loons (Gavia immer) and bald eagles (Haliaeetus leucocephalus): Ecotoxicology, v. 17, no. 

2, p. 93–101. 

Scheuhammer, A.M., Meyer, M.W., Sandheinrich, M.B., and Murray, M.W., 2007, Effects of 

environmental methylmercury on the health of wild birds, mammals, and fish: AMBIO—A Journal of 

the Human Environment, v. 36, no. 1, p. 12–19. 

Schwanke, C.J., and McCormick, M.B., 2010, Stock assessment and biological characteristics of burbot 

in Tanada Lake, 2007 and Copper Lake, 2008: Anchorage, Alaska Department of Fish and Game 

Fishery Data Series No. 10-62, Final Report for Study 07-501. 

Schwindt, A.R., Fournie, J.W., Landers, D.H., Schreck, C.B., and Kent, M.L., 2008, Mercury 

concentrations in salmonids from western US national parks and relationships with age and 

macrophage aggregates: Environmental Science and Technology, v. 42, no. 4, p. 1,365–1,370. 

Scott, W.B., and Crossman, E.J., 1973, Freshwater fishes of Canada: Fisheries Research Board of 

Canada Bulletin, v. 184. no. 86, p. 1,026. 

Snodgrass, J.W., Jagoe, C.H., Bryan, A.L., Brant, H.A., and Burger, J., 2000, Effects of trophic status 

and wetland morphology, hydroperiod, and water chemistry on mercury concentrations in fish: 

Canadian Journal of Fisheries and Aquatic Sciences, v. 57, p. 171–180. 
24

Sousanes, P., 2012, Annual climate summary 2008—Central Alaska Network: National Park Service 

Natural Resource Data Series NPS/CAKN/NRDS—2012/245. 

Ullrich, S.M., Tanton, T.W., and Abdrashitova, S.A., 2001, Mercury in the aquatic environment—A 

review of factors affecting methylation: Critical Review in Environmental Science and Technology, v. 

31, no. 3, p. 241293. 

U.S. Environmental Protection Agency, 2000, Method 7473, Mercury in solids and solutions by thermal 

decomposition, amalgamation, and atomic absorption spectrophotometry, test methods for evaluating 

solid waste, physical/chemical methods SW 846: U.S. Environmental Protection Agency, Update 

IVA.

Vander Zanden, M.J., and Rasmussen, J.B., 1996, A trophic position model of pelagic food webs—

Impact on contaminant bioaccumulation in lake trout: Ecological Monographs, p. 451–477. 

Verbrugge, L.A., 2007, Fish consumption advice for Alaskans—A risk management strategy to 

optimize the public's health: State of Alaska Epidemiology Bulletin, v. 11, no. 4, p. 1–39. 

Watras, C.J., Back, R.C., Halvorsen, S., Hudson, R.J.M., Morrison, K.A., and Wente, S.P., 1998, 

Bioaccumulation of mercury in pelagic freshwater food webs: Science of the Total Environment, v. 

219, nos. 2–3, p. 183–208. 

Weeks, D.P., 2003, Wrangell-St. Elias National Park and Preserve, Alaska, Water resources scoping 

report: National Park Service, Technical Report NPS/NRWRD/NRTR-2003/213, 114 p. 

Wiener, J.G., Knights, B.C., Sandheinrich, M.B., Jeremiason, J.D., Brigham, M.E., Engstrom, D.R., 

Woodruff, L.G., Cannon, W.F., and Balogh, S.J., 2006, Mercury in soils, lakes, and fish in Voyageurs 

National Park (Minnesota)—Importance of atmospheric deposition and ecosystem factors: 

Environmental Science and Technology, v. 40, p. 6,261–6,268. 

Wiener, J., and Spry, J., 1996, Toxicological significance of mercury in freshwater fish, in Beyer, W.N, 

Heinz, G.H., and Redmon-Norwood, A.W., eds, Environmental contaminants in wildlife—

Interpreting tissue concentrations: Boca Raton, Florida, Lewis Publishers, p. 297–339. 
25

Appendix 1. Equations for Converting Standard Length (SL, in millimeters) to 

Total Length (TL, in millimeters) for Four Species of Fish Sampled from 

Wrangell-St. Elias National Park and Preserve, Alaska.

Arctic grayling: TL = 1.0312 * SL + 23.116; n = 10; R2 = 0.9944; P < 0.0001 

burbot: TL = 1.11 * SL + 7.6252; n = 24; R2 = 0.9866; P < 0.0001 

lake trout: TL = 1.1643 * SL + 18.84; n = 30; R2

 = 0.9754; P < 0.0001 

rainbow trout: TL = 1.1386 * SL + 4.6143; n = 15; R2 = 0.9974; P < 0.0001 
26

Appendix 2. Size at Which the Proportion of Modeled Individuals of Each 

Species from Tanada Lake Exceeded Defined Toxicity Benchmarks in WrangellSt. Elias National Park and Preserve, Alaska.

Fish Toxicity

NOERa

(200 ng/g)

LOERb

(300 ng/g)

Species 0% 50% 100% 0% 50% 100%

Arctic grayling -- -- -- -- -- --

burbot 370 492 559 463 -- --

lake trout 356 398 470 432 -- -- a No-Observed-Effects-Residue (Beckvar and others, 2005). b Lowest-Observed-Effects-Residue (Sandheinrich and others, 2011).

Bird Toxicity

High Sensitivity

(90 ng/g)

Moderate Sensitivity

(180 ng/g)

Low Sensitivity

(270 ng/g)

Species 0% 50% 100% 0% 50% 100% 0% 50% 100%

Arctic grayling 308 336 -- -- -- -- -- -- --

burbot < 345 < 345 377 346 468 535 439 561 --

lake trout < 330 < 330 < 330 337 378 450 413 454 --

Human Toxicity

Unrestricted Consumption

(150 ng/g)

4 Meals per Week

(320 ng/g)

2 Meal per Week

(640 ng/g)

Species 0% 50% 100% 0% 50% 100% 0% 50% 100%

Arctic grayling 315 -- -- -- -- -- -- -- --

burbot < 345 < 345 396 365 484 546 503 -- --

lake trout < 330 < 330 335 348 391 459 461 -- --

-- Denotes that none of the population were modeled to exceed the benchmark at even the largest size 

observed.

< Denotes that 100 percent of the population were modeled to exceed the benchmark at even the smallest size 

observed.
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Kowalski and others—Mercury in Fishes from Wrangell -St. Elias National Park and Preserve, Alaska—Open-File Report 2014–1145

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141145