Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables

MPB-07995; No of Pages 7 Marine Pollution Bulletin xxx (2016) xxx–xxx

Contents lists available at ScienceDirect

Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables Rebecca Bentzen a,b, J. Margaret Castellini c,⁎, Robert Gerlach d, Claude Dykstra e, Todd O'Hara c a

Institute of Arctic Biology, P.O. Box 757000, University of Alaska Fairbanks, Fairbanks, AK 99775-7000, USA Arctic Beringia Program, Wildlife Conservation Society, P.O. Box 751110, Fairbanks, AK 99775, USA Department of Veterinary Medicine, P.O. Box 757750, University of Alaska Fairbanks, Fairbanks, AK 99775-7750, USA d Office of the State Veterinarian, Alaska Dept. of Environmental Conservation, 5251 Dr. Martin Luther King Jr. Ave., Anchorage, AK 99507, USA e International Pacific Halibut Commission, 2320 W. Commodore Way, Suite 300, Seattle, WA 98199-1287, USA b c

a r t i c l e

i n f o

Article history: Received 17 November 2015 Received in revised form 12 July 2016 Accepted 26 August 2016 Available online xxxx Keywords: Mercury C and N stable isotopes Pacific halibut Alaska Feeding ecology

a b s t r a c t Total mercury concentrations ([THg]), δ15N and δ13C values were determined in muscle of 693 Pacific halibut caught in International Pacific Halibut Commission setline surveys in Alaska (2002−2011). Project goals were to evaluate whether 1) δ15N and δ13C varied with region, age, sex and length of halibut, and 2) muscle [THg] varied with δ15N and δ13C (feeding ecology) while accounting for sex, length, and region. Variation in [THg] was explained, in part, by halibut feeding ecology as [THg] increased with trophic position (increasing δ15N). Halibut from the western Aleutian Island region were the exception, with overall lower δ15N values and significantly higher [THg] than halibut from other Alaskan waters. This [THg] pattern has been observed in other Aleutian biota, possibly the result of northeasterly atmospheric movement of mercury emissions from Asia and/or other local sources and processes. The significantly lower δ15N values for these halibut warrants further investigation of halibut prey. © 2016 Elsevier Ltd. All rights reserved.

1. Introduction Pacific Halibut (Hippoglossus stenolepis; hereafter, halibut) are one of the world's largest flatfish, reaching 2.5 m in length and over 200 kg in weight, and living up to 55 years. Females reach maturity between ages 12 and 15 years (Keith et al., 2014). Typical commercial caught halibut in Alaska range between 10 and 170 lb. (5 to 77 kg) with averages closer to 28 lb. (13 kg), round weight (intact fish). This species supports one of the most important commercial fisheries on the west coast of the United States of America and Canada with an annual catch limit of 40– 75 million lb. (18–34 million kg) net weight (head off, viscera removed) over the past decade [IPHC (2015); www.iphc.int]. These halibut are also caught in both sport and subsistence fisheries. In 2012 the combined U.S. recreational and commercial harvest of 34 million lb. was valued at $153 million dollars (NOAA, 2015) (We note the International Pacific Halibut Commission (IPHC) and the National Oceanic and Atmospheric Administration (NOAA) present catch data differently and thus cannot be directly compared). Inorganic forms of mercury (Hg) enter ecosystems through natural sources such as volcanism, and anthropogenic sources such as mining ⁎ Corresponding author. E-mail addresses: [email protected] (R. Bentzen), [email protected] (J.M. Castellini), [email protected] (R. Gerlach), [email protected] (C. Dykstra), [email protected] (T. O'Hara).

and coal combustion (AMAP, 2011) and are generally converted to the more toxic and bioavailable monomethyl mercury (MeHg+) by bacteria after deposition (AMAP, 2011). Dietary MeHg+ is readily absorbed in humans (Aberg et al., 1969), and at high exposure levels can damage the developing nervous system (Kjellström, 1991; McKeown-Eyssen et al., 1983; Stewart et al., 2003). Thus, potential toxicity in consumers is one of the main driving forces to address Hg in halibut. In general, fish are an excellent source of lean protein, omega-3 fatty acids, antioxidants, and vitamins (Hamade, 2014). More specifically for pregnant and nursing women and young children the omega-3 fatty acids in fish improve maternal nutrition and fetal and neonatal brain development (Alessandri et al., 2004; Myers et al., 2007). Furthermore, many Alaska Native people have a strong reliance on fish as part of their traditional way of life and subsistence diet; as well as commercial enterprises. However, concerns about the health risks of Hg have prompted many states, and several federal agencies, to advise the public to limit consumption of certain fish, including some size classes of Alaska halibut (Hamade, 2014), since consumption of fish that accumulate MeHg+ in muscle is the primary pathway of exposure to Hg in most humans (Wagemann et al., 1997). Some of these fish consumption advisories do not consider biological variation in fish that impact Hg concentrations and many ignore the known benefits of consuming fish. Stable isotopes analysis of carbon (δ13C) and nitrogen (δ15N) are used to evaluate movement between geographically distinct ecosystems and feeding ecology (Abend and Smith, 1995; Dehn et al., 2002;

http://dx.doi.org/10.1016/j.marpolbul.2016.08.068 0025-326X/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

2

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

Hilderbrand et al., 1996; Hobson and Schell, 1998; Pond and Gilmour, 1997). Some portion of adult halibut continue to disperse, typically to the east, however, this degree of movement should not impact our study, given the scale at which C and N stable isotopes allow interpretation. Changes in δ13C can provide information on the geographic location of dietary resources as δ13C values of sediments typically vary predictably along a gradient (Dehn et al., 2002; Dunton et al., 1989; Naidu et al., 1993; Schell et al., 1998). Enrichment of δ15N can be used to estimate relative trophic position; there is generally an increase on the order of 3‰–5‰ in δ15N values with each trophic level transfer (Hobson and Welsh, 1992; Kelly, 2000; Kurle and Worthy, 2002), providing a relatively long-term measure of the trophic position of an organism integrated over time (Atwell et al., 1998; Pond and Gilmour, 1997). This approach can greatly enhance interpretation of total mercury concentration ([THg]) data when seeking to describe general feeding ecology and determine major drivers of Hg exposure in a long lived piscivore. Age, size, and food web (trophic transfer) dependent processes are known to correlate with increases in [THg] in some piscivores (e.g. halibut) as reported by the Arctic Marine Assessment Programme (AMAP, 2011). Thus older, likely larger halibut, are expected to have higher [THg] both because they have had more time to accumulate [THg] (age-dependent) and because they are feeding at a higher trophic level (as measured by increases in δ15N). In general, Pacific halibut consume plankton their first year of life, switching to euphausiids and small fish from ages 1 to 3 years old. Halibut consume more and larger fish as they grow, including herring, sandlance, capelin, smelt, pollock, sablefish, cod, rockfish, octopus, crabs and clams [ADF&G (2015); www. adfg.alaska.gov]. The goals of this project were 1) to evaluate whether δ15N and δ13C values varied with geographic region, age, sex and length of halibut from waters around Alaska, and 2) to evaluate whether [THg] in the muscle varied with the relative trophic position of the halibut (e.g. δ15N and δ13C values) while accounting for sex, length, and region. We expect that δ13C and δ15N values in halibut muscle will vary by age

(reflecting their changing trophic position), and by region, as carbon isotopes vary by region and because halibut prey types may vary by region. Additionally, male and female halibut are sexually dimorphic and may consume different prey and thus vary in δ15N and δ13C values that will be reflected in [THg] in muscle. This report does not address the risk or benefits to human consumers of halibut as this is done via the State of Alaska (Hamade, 2014). 2. Methods 2.1. Study area and sample selection The Alaska Department of Environmental Conservation, Fish Monitoring Program in collaboration with the IPHC collected and analyzed halibut samples from 2002 to 2011 from across the coast of Alaska. Halibut samples were collected from IPHC regulatory areas (Kong et al., 2004) aboard standard grid survey vessel operations during 2002 to 2011 (Fig. 1). The goal was to collect samples from fish in the 20 to 40 lb. (~ 9 to 18 kg) and the 40 to 100 lb. (~ 18 to 45 kg) category. All muscle samples came from fish targeted for an age sample (otolith) and were free from any gross abnormalities or disease. After processing the fish using standard protocols and collecting the otolith for age determination, samplers collected a 2 to 3 lb. (~1 to 1.5 kg) muscle sample from the anterior of the fish, just caudal of the gill plate, while wearing nitrile gloves. The sample was stored in a food grade plastic bag, labeled and frozen. Care was taken in all cases to avoid any gross contamination of the fish with bilge, wastewater, fuel or exhaust emissions. Upon landing the frozen samples were shipped to the Alaska Environmental Health Laboratory (EHL) in Anchorage. Fig. 2 illustrates where the IPHC regulatory areas were further subdivided into regions for this comparative study. The comparative regions are described in Table 1. We selected samples for this study using a stratified sampling approach, randomly selecting 10 samples from each sex (male, female) and size cohorts (b 20 lb., 20–40 lb., 40–50 lb., 50–90 lb., N 90 lb.; b9.1 kg, 9.1–18.2 kg, 18.2–22.7 kg, 22.7–40.9 kg, N40.9 kg) within

Fig. 1. International Pacific Halibut Commission regulatory areas, 1999–2004. [Revised from IPHC (2015)].

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

3

Fig. 2. Regional catch areas for Alaskan halibut caught on commercial fisheries grounds in Alaskan waters between 2002 and 2011 for comparative analysis (Kahle and Wickham, 2013; www.openstreetmap.org). AI: Aleutian Islands, AK: Alaska, BS: Bering Sea, GOA: Gulf of Alaska, PWS: Prince William Sound, SE: Southeast.

each of the 14 regions. If there were fewer than 10 samples available within a sampling unit, we included all of the individuals. This approach was chosen to assure that all regions, sexes, and size-classes were represented in the dataset. 2.2. Laboratory analyses Halibut tissue samples were stored at −20 °C or less prior and after shipping to the Alaska State EHL. Standard laboratory procedures following Environmental Protection Agency (EPA) guidelines (EPA-B-00007) were used to process fish samples. After thawing at 4 °C and trimming outer layers, skinless muscle tissue was homogenized a minimum of three times using a commercial grade stainless steel grinder and

stored in pre-cleaned 4 oz. glass sample jars (I-CHEM pre-cleaned sample jars with certificate of analysis). Total mercury concentration ([THg]) in the wet tissue samples was determined using a DMA-80 (Milestone Inc., Shelton, CT) direct mercury analyzer following EPA method 7473 (U.S. EPA, 2007). Quality-assurance measures included analysis of a certified reference material (DORM-3 & DORM-4; National Research Council of Canada, Ottawa, Canada), three method blanks, and two duplicates per batch of 20 samples. Recoveries for certified reference material ranged from 90–110% for initial calibration verifications and 80–120% for continuing calibration verifications. The absolute relative percent difference (RPD) was ≤ 20% for duplicates with one rerun allowed. Approximately 0.1 to 0.2 g (±0.02 g) of sample was placed in a quartz boat that was inserted

Table 1 Description of catch areas for halibut caught on commercial fishing grounds within the International Pacific Halibut Commission (IPHC) regulatory areas in Alaska. Region

IPHC regulatory area

Samples collected

Southeast inshore

Area 2C: Ketchikan, Ommaney, Sitka stations Area 2C: Ketchikan, Ommaney, Sitka stations Area 3A: Yakutat and Fairweather stations Area 3A: southern PWS stations Area 3A: northern PWS stations

South of Cape Spencer to the Canadian Border to the east of a line extending south from Glacier Bay south to 66 Clarence Strait (Inside Passage) South of Cape Spencer to the Canadian Border to the west of a line extending south from Glacier Bay south to 203 Clarence Strait (Inside Passage) South of Kayak Island to Cape Spencer (Cross Sound) 182 South of Hinchinbrook Island to Kayak Island In PWS inshore from Hinchinbrook and Montague Islands

31 74

Area 3A: Seward stations Area 3A: Gore Point stations

West of Montague Island to Southern tip of the Kenai Peninsula Northeast of Kodiak Island to South of the Seward Area

60 40

Area 3A: Shelikof stations Area 3A: Portlock, Albatross, Trinity stations Area 3B Area 4A: Unalaska stations

North of Port Graham in Cook Inlet

56 157

Area 3B inclusive (Semidi, Chignik, Shumagin, Sanak stations) Southeastern end of Unalaska Island west to the Islands of the 4 Mountains

185 68

Area 4A: Adak and Attu stations Area 4C: St. Paul stations Areas 4D, 4A: 4A Edge and 4D Edge stations

Adak Island west to Attu Island immediately around St Paul Island North of Aleutian Island, Akutan to South of St George Island (4A stations) then Northeast of St Paul (4D stations)

268 56 128

Southeast offshore Yakutat Cordova Prince William Sound (PWS) Seward Gulf of Alaska, Offshore Homer/Cook Inlet Kodiak Alaska Peninsula Eastern Aleutian Islands Western Aleutians Pribilof Islands Offshore Bering Sea

n

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

4

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

into the decomposition furnace, which thermally and chemically decomposed the samples at 200 °C for 1–2 min. Flowing oxygen carried the decomposition products to the catalyst furnace, which trapped halogens and nitrogen/sulfur oxides. The remaining products were then carried to a gold amalgamator, which selectively trapped mercury. The system was flushed with oxygen after which the amalgamator was heated to 650 °C to release the mercury vapors that were passed through a spectrophotometer that measured absorbance at 253.7 nm and determined mercury content. This method determines total mercury content and does not differentiate between inorganic mercury and methylmercury. The halibut homogenate samples (n = 693) were analyzed for stable isotopes of nitrogen (N) and carbon (C); 0.25–0.5 mg of lyophilized muscle was weighed into tin cups (Elemental Microanalysis, Cambridge, UK) and analyzed at the Alaska Stable Isotopes Facility at the University of Alaska Fairbanks. An elemental analyzer–isotopic ratio mass spectrometer (Costech Elemental Analyzer [ESC 4010] and Finnigan MAT Conflo III interface with a Delta + XP mass spectrometer) was used (Cardona-Marek et al., 2009; Rea et al., 2013). The ratio of stable isotopes is expressed in delta (δ) notation and calculated as: δX ¼




 Rsample =Rstandard −1  1000

where X = 15N or 13C and R = 15N/14N or 13C/12C in the sample and standard. 2.3. Statistical analysis General linear models (PROC GLM; SAS 9.1.3) were used to evaluate whether δ13C and δ15N stable isotopes values (n = 693) vary by region, age, sex, length and interactions using 2 separate a priori candidate model sets, each with 16 models. The variables age and length were not included in the same model as they are correlated, or the variable year as only a few regions were sampled in any one year confounding the variables year and region. Models in the two candidate sets included all additive combinations of the variables (e.g. δ15Nregion; δ15Nregion + age; age; δ13Cregion; δ13Cregion + age) and 3 models that included interaction terms between all variables in the top additive model (e.g. δ15 Nlength + sex + region + length ∗ sex). δ15N and δ13C values were square root-transformed and a constant 23 was added to δ13C values to improve normality. General linear models were used to evaluate the relationship between δ13C and δ15N stable isotopes and [THg] in Alaskan Pacific halibut (n = 693), while controlling for length, age, sex, and region using a hierarchical approach. Again, age and length were not included in the same model or the variable year as for the reasons stated above. All additive combinations of the variables length, age, sex, and region were included (e.g. Modelsex; Modelsex + region; Modelsex + region + length; Modelsex + region + age), as were models that included interaction terms between all variables in the top additive model (e.g. Modelage + sex + region + age ∗ sex; Modelage + sex + region + sex ∗ region; Modelage + sex + region + age ∗ region), and lastly, three models that included δ13C and δ15N values individually and together (e.g. Modeltopmodel + N; Modeltopmodel + C; Modeltopmodel + N + C). This allowed us to examine the effect of δ13C and δ15N values while controlling for variables that are known to explain some variation in [THg]. [THg] was log transformed to improve normality. Akaike's information criterion (AIC) was used to select the best approximating models as it allowed us to evaluate a number of competing nested models without violating the rules of multiple comparisons and error rates (Burnham and Anderson, 2002). 3. Results

14.88‰ (Median = 15.05‰, SE = 0.06, SD = 1.46, n = 693) and ranged from 10.37 to 18.38‰. δ13C averaged − 17.99 (Median = − 17.79‰, SE = 0.05, SD = 1.40) and ranged from −22.97 to −14.47. [THg] averaged 0.32 μg g−1 (Median = 0.23, SE = 0.01, SD = 0.27) and ranged from 0.13 to 1.75 μg g−1 (wet weight). The best approximating a priori model describing variation in δ15N in halibut muscle included length, sex, region and an interaction between length and region and was 14.06 AIC units from the next best model, which did not include the interaction term (Table 2). δ15N values increased with length (F = 53.18, p b 0.0001), were higher in females (F = 6.44, p = 0.01), and varied by region (F = 654, p b 0.0001), and with the interaction between length and region (F = 3.04, p = 0.0002; Fig. 3). The best approximating a priori model describing variation in δ13C in halibut included age, sex, region and an interaction between age and sex, but was only 0.51 AIC units from the next best model, which did not include the interaction term and 3.25 AIC units from the third best model (δ13Cage + sex + region + age ∗ region; Table 3). The top two models carried 0.90 of the AIC model weight (Table 3). δ13C values decreased with age (F = 13.54, p b 0.001), were enriched in females (F = 7.59, p = 0.006), and varied by region (F = 81.76, p b 0.0001). However, the interaction between age and sex was not significant (F = 2.41, p = 0.12). The best approximating a priori model describing [THg] in Alaskan halibut included age, sex, region, δ15N, and an interaction between age and sex and was 1.15 AIC units from the next best model, which included δ13C and 8.12 AIC units from the next best model which included δ13C but not δ15N (Table 4). These top 3 models carried all the weight (∑ wi = 1.0). [THg] varied significantly by region (F = 18.84, p b 0.001; Fig. 4), increased with age in female more so than male halibut (F = 20.10, p b 0.001; Fig. 5), increased with δ15N (F = 13.08, p = 0.0003; Fig. 6) but did not vary with δ13C (F = 0.83, p = 0.36). 4. Discussion Total mercury concentrations ([THg]) in halibut caught on IPHC setline surveys from commercial grounds around Alaska between 2002 and 2011 were variable (ranging from 0.13 to 1.75 μg g−1 ww) and differed by geographic region, age (size), and feeding ecology as determined by C and N stable isotope ratios. Mercury concentrations were similar to those reported from Greenland halibut caught off the coast of Norway in 2006 (average 0.23 μg g−1, Julshamn et al. (2011); this study, 0.32 μg g−1), and as expected, older (larger) fish were feeding at a higher trophic level (greater δ15N) and had higher [THg] in muscle. Table 2 A priori models describing variation in δ15N in halibut caught on commercial fisheries grounds in Alaskan waters between 2002 and 2011. Factors in models included length, age, sex, and region of Alaska. Model

Ka

AICb

ΔAICc

wid

Length, sex, region, length ∗ region Length, sex, region Length, sex, region, length ∗ sex Length, region Length, sex, region, sex ∗ region Age, sex, region Sex, region Age, region Region Length, sex Sex Age, sex Age Length

30 17 18 16 30 17 16 16 15 4 3 4 3 3

−2838.40 −2824.34 −2822.39 −2821.55 −2829.21 −2789.95 −2779.53 −2757.46 −2757.47 −2313.26 −2306.33 −2304.70 −2275.90 −77.02

0.00 14.06 16.01 16.85 9.19 48.45 58.87 80.94 80.93 525.14 532.07 533.70 562.50 2761.38

0.99 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

a b

Carbon and nitrogen stable isotope values and [THg] were measured in 693 halibut of known age, sex, length, and region. δ15N averaged

c d

No. of parameters in the model. Akaike's information criterion. Difference between model AIC and AIC value of the best model. AIC wt.

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

18.5

Table 4 A priori models describing [THg] in Alaskan halibut caught on commercial fisheries grounds in Alaskan waters between 2002 and 2011. Factors in models included length, age, sex, region of Alaska and δ13C and δ15N values.

17.5 16.5

δ 15N

15.5 14.5 13.5 12.5

11.5 10.5 60

85

110

135

160

185

Length (cm) Fig. 3. δ15N values vary by length in halibut (males shown here) caught on commercial fisheries grounds in Alaskan waters between 2002 and 2011 and are much lower in the Western Aleutian Islands (dashed line) than all other regions (solid lines) that are overlapping. Lines are truncated at the smallest and largest halibut in the dataset within each region.

Model

Ka

AICb

ΔAICc

wid

Age sex, region, age ∗ sex N Age sex, region, age ∗ sex N C Age sex, region,age ∗ sex C Age sex, region, age ∗ sex Age sex, region, sex ∗ region Age, sex, region, age ∗ region Age, sex, region Age, region Length, sex, region Age, sex Age Length, region Length, sex Length Sex, region Region Sex

19 20 19 18 30 30 17 16 17 4 3 16 4 3 16 15 3

−911.08 −909.93 −902.96 −899.78 −872.22 −871.82 −862.44 −840.80 −733.21 −684.29 −679.88 −650.03 −605.22 −505.41 −484.47 −478.70 −378.06

0.00 1.15 8.12 11.30 38.86 39.26 48.64 70.28 177.87 226.79 231.20 261.05 305.86 405.67 426.61 432.38 533.02

0.63 0.36 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

a b c d

Table 3 A priori models describing variation in δ13C in halibut caught on commercial fisheries grounds in Alaskan waters between 2002 and 2011. Factors in models included length, age, sex, and region of Alaska.

No. of parameters in the model. Akaike's information criterion. Difference between model AIC and AIC value of the best model. AIC wt.

with a large net emigration of halibut out of Area 4A and into Area 2B [Valero and Webster (2012); see Fig. 2]. Halibut also move between regions annually, however, halibut are very long lived and those older than age eight often show summer feeding ground fidelity (Loher, 2008), with most commercially caught halibut being older than eight years. Adult summer feeding ground fidelity likely explains the regional differences we have noted in muscle chemistry. There were significant differences in the feeding ecology biomarkers (δ15N and δ13C) of halibut around Alaska. Based on the significant differences in δ15N values the relative trophic level position varied between regions with western Aleutian Island halibut feeding predicted to be at the lowest trophic position, regardless of age or sex (~ 2‰ lower). We hesitate to outright conclude the difference is completely trophic level derived, as δ15N values could potentially vary by region at the levels of primary production or primary consumers and be reflected in the halibut. Based on the low δ15N-values from this region the halibut diets may include smaller, lower trophic level fish. Diet differences between Gulf of Alaska and Aleutian halibut were found in the early 1990s with Aleutian halibut consuming primarily cephalopods and Atka mackerel (fish comprised b 50% of the diet) while Gulf of Alaska halibut consumed primarily walleye pollock [fish comprised ~ 64% of their diet; Yang (1996)]. However, the diet differences from that one 0.6 -1

Additionally, female halibut fed at a higher trophic level than males at all ages, and this was reflected in a greater [THg] in female halibut at any given age, as was also seen in the Greenland halibut (Julshamn et al., 2011); this is likely due to the fact that female halibut grow faster and so are larger at a given age than males (Bowering and Nedreaas, 2001) but other sex-dependent processes may be involved with the toxicodynamics of Hg as well. There were significant differences in both [THg] and chemical feeding ecology biomarkers between regions suggesting they could be useful when evaluating advisory limits for consumption of halibut to limit mercury intake. For example, the halibut caught in the offshore Gulf of Alaska region were relatively low in [THg] and this region is also the area with the greatest commercial catch in Alaskan waters, at approximately 40% of total coast-wide harvest quota set by the IPHC (IPHC, 2012). Halibut are certainly moving between the IPHC regulatory areas; in Alaskan waters, after spawning, halibut eggs and larvae are carried north and westward by ocean currents towards the western Gulf of Alaska and the Bering Sea. Then, clockwise migration during development of juvenile and younger halibut from west to east continues beyond age eight [see Valero and Webster (2012)]. The rates of movement are greatest for the western regulatory areas in the Gulf of Alaska

0.5

Ka

AICb

ΔAICc

wid

0.4

Age, sex, region, age ∗ sex Age, sex, region Age, sex, region, age ∗ region Sex, region Age, region Length, sex, region, sex ∗ region Length, sex, region Length, region Region Age, sex Age Length, sex Sex Length

18 17 30 16 16 30 17 16 15 4 3 4 3 3

−2159.04 −2158.53 −2155.79 −2145.29 −2144.18 −2143.95 −2143.41 −2114.53 −2113.50 −1532.27 −1520.92 −1506.53 −1501.46 −1465.18

0.00 0.51 3.25 13.75 14.86 15.09 15.63 44.51 45.54 626.77 638.12 652.50 657.58 693.86

0.51 0.39 0.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.3

b c d

No. of parameters in the model. Akaike's information criterion. Difference between model AIC and AIC value of the best model. AIC wt.

[THg]

Model

a

5

0.2 0.1 0

Fig. 4. Least squares means and standard errors from the top model (Modelage + sex + region + δ15N + age ∗ sex) describing variation in [THg] in muscle (wet weight) in halibut caught on commercial grounds in Alaskan waters between 2002 and 2011.

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

6

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx

3

-1

2.5 Females

[THg]

2 1.5

Males

1 0.5 0 6

10

14

18

22

26

30

34

Age (years) Fig. 5. Predicted [THg] by age in halibut caught on commercial grounds in Alaskan waters between 2002 and 2011 across ages and between sexes controlled for region, δ15N, and δ13C. Shown is estimated [THg] from the a priori model describing [THg] in Alaskan halibut (n = 693) including the variables age, sex, region, δ15N, and an interaction between age and sex and δ13C, for halibut caught near Yakutat, AK, of mean δ15N- and δ13C-values. Yakutat was chosen because it is the middle of the grouping of halibut regions both geographically and by [THg].

year study do not adequately explain the large difference in δ15N values in halibut between regions. We cannot completely understand what is driving the variation in nitrogen isotopes in the western Aleutian chain without specific prey carbon and nitrogen isotope data from this region. Although western Aleutian halibut appear to be feeding at a relatively low trophic position, they had significantly higher [THg], which were not explained by feeding ecology, age, or sex. This mirrors a trend where concentrations of some contaminants in other biota increased westward along the chain (Anthony et al., 1999; Anthony et al., 2007; Ricca et al., 2008; Rocque and Winker, 2004) and as evidenced by regional differences in [THg] in hair and blood of Steller sea lions (Castellini et al., 2012; Rea et al., 2013). This pattern has been attributed to atmospheric transport as weather systems that form in this region pull storms and contaminants from Asia eastward along the archipelago (AMAP, 2002); however we recognize there are other natural sources and processes to consider (e.g., volcanism, geologic deposits, marine Hg methylation). Halibut in the western Aleutian Islands have lower dispersal rates than other regions, possibly because the Amukta and Amchitka Passes and Near Strait may serve as physical oceanographic barriers to limit west-east migration of adults (Loher and Clark, 2010). Given the higher [THg] in the western Aleutian population as well as low dispersal rates, regionally-based drivers of these [THg] differences require investigation when other more commonly accepted drivers such as trophic level, age/

size, and sex cannot explain regional differences whether they are significantly higher or lower than the majority of the regions surveyed. Additionally, the halibut collected in the Pribilof region had the lowest [THg], and this difference was not explained by their trophic position based on δ15N. It is possible this may be explained by biotransport and processes that affect Hg bioavailability [see AMAP (2011)], however, this will require further investigation. It is interesting that the offshore Bering Sea caught halibut have higher [THg] than those collected in the Pribilof region (see Fig. 1). In contrast to our findings, an earlier study found that northern fur seals in the Pribilofs had higher [THg] than Steller sea lions in Prince William Sound and southeast Alaska (Beckmen et al., 2002), however it is possible that this is due to differences in the two pinniped species diets and age of individuals. In conclusion, δ15N and δ13C values did vary with geographic region, age, sex and length and variation in [THg] in muscle can be explained, in part, by feeding ecology of the halibut; as expected, the [THg] in halibut muscle generally increased with trophic position. The western Aleutian island region stood out from the rest of Alaska in that halibut had the lowest δ15N values (possibly feeding at a lower trophic position) but had the highest [THg] in muscle than did halibut in other Alaskan waters. This requires further investigation related to the feeding ecology of Hg in halibut and other marine top predators.

Acknowledgements This work was funded by the Alaska Department of Environmental Conservation, in part with qualified outer continental shelf oil and gas revenues by the Coastal Impact Assistance Program within the Department of the Interior's U.S. Fish and Wildlife Service, (Grant # F12AF70098). The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Government. Publication costs were provided by the office of the Vice Chancellor of Research at the University of Alaska Fairbanks. Thanks to the collection efforts of the IPHC, their hired sea samplers, and vessel skippers and crew in the collection of samples throughout Alaska. We thank the Alaska Department of Environmental Conservation, Environmental Health Laboratory staff who participated in processing and analyzing these samples, especially Howard Teas who helped coordinate the logistics for this study. We thank students in the Wildlife Toxicology Lab at the University of Alaska Fairbanks, especially Andrew Cyr, who coordinated and processed samples for C and N stable isotope analysis.

References

[THg]

-1

0.35

0.3

0.25

0.2

0.15

δ 15N Fig. 6. [THg] in relation to δ15N values in halibut caught in commercial fisheries in Alaskan waters between 2002 and 2011. Shown is estimated [THg] from the a priori model describing [THg] in Alaskan halibut (n = 693) including the variables age, sex, region, δ15N, and an interaction between age and sex and δ13C, for an average 18 year-old male halibut of mean δ13C values in the Yakutat region. Yakutat was chosen because it is the middle of the grouping of halibut regions both geographically and by [THg].

Abend, A.G., Smith, T.D., 1995. Differences in ratios of stable isotopes of nitrogen in longfinned pilot whales (Globicephala melas) in the western and eastern North Atlantic. ICES J. Mar. Sci.: Journal du Conseil 52, 837–841. Aberg, B., Ekman, L., Falk, R., Greitz, U., Persson, G., Snihs, J.-O., 1969. Metabolism of methyl mercury (203Hg) compounds in man. Arch. Environ. Health 19, 478–484. ADF&G, 2015. Alaska Department of Fish and Game Website. State of Alaska. (www.adfg. alaska.gov). Alessandri, J.M., Guesnet, P., Vancassel, S., Astorg, P., Denis, I., Langelier, B., Aid, S., PoumesBallihaut, C., Champeil-Potokar, G., Lavialle, M., 2004. Polyunsaturated fatty acids in the central nervous system: evolution of concepts and nutritional implications throughout life. Reprod. Nutr. Dev. 44, 509–538. AMAP, 2002. Arctic Pollution 2002: Persistant Organic Pollutants, Heavy Metals, Radioactivity, Human Health, Changing Pathways. Arctic Monitoring and Assessment Programme (AMAP), Oslo, Norway, p. xii + 112. AMAP, 2011. AMAP Assessment 2011: Mercury in the Arctic. Arctic Monitoring and Assessment Programme (AMAP), Oslo, Norway, p. xiv + 193. Anthony, R.G., Miles, A.K., Estes, J.A., Isaacs, F.B., 1999. Productivity, diets, and environmental contaminants in nesting bald eagles from the Aleutian archipelago. Environ. Toxicol. Chem. 18, 2054–2062. Anthony, R.G., Miles, A.K., Ricca, M.A., Estes, J.A., 2007. Environmental contaminants in bald eagle eggs from the Aleutian archipelago. Environ. Toxicol. Chem. 26, 1843–1855. Atwell, L., Hobson, K.A., Welch, H.E., 1998. Biomagnification and bioaccumulation of mercury in an arctic marine food web: insights from stable nitrogen isotope analysis. Can. J. Fish. Aquat. Sci. 55, 1114–1121.

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068

R. Bentzen et al. / Marine Pollution Bulletin xxx (2016) xxx–xxx Beckmen, K.B., Duffy, L.K., Zhang, X., Pitcher, K.W., 2002. Mercury concentrations in the fur of Steller sea lions and northern fur seals from Alaska. Mar. Pollut. Bull. 44, 1130–1135. Bowering, W.R., Nedreaas, K.H., 2001. Age validation and growth of Greenland halibut (Reinhardtius hippoglossoides (Walbaum)): a comparison of populations in the Northwest and Northeast Atlantic. Sarsia 86, 53–68. Burnham, K.P., Anderson, D.R., 2002. Model Selection and Multimodel Inference: a Practical Information-Theoretic Approach. 2nd ed. Springer-Verlag, New York, NY, USA. Cardona-Marek, T., Knott, K.K., Meyer, B.E., O'Hara, T.M., 2009. Mercury concentrations in southern Beaufort Sea polar bears: variation based on stable isotopes of carbon and nitrogen. Environ. Toxicol. Chem. 28, 1416–1424. Castellini, J.M., Rea, L.D., Lieske, C.L., Beckmen, K.B., Fadely, B.S., Maniscalco, J.M., O'Hara, T.M., 2012. Mercury concentrations in hair from neonatal and juvenile Steller sea lions (Eumetopias jubatus): implications based on age and region in this northern Pacific marine sentinel piscivore. EcoHealth 9, 267–277. Dehn, L.A., George, J.C., Solomon, K.R., Muir, D.C.G., O'Hara, T.M., Hoekstra, P.F., 2002. Trophic ecology of bowhead whales (Balaena mysticetus) compared with that of other arctic marine biota as interpreted from carbon-, nitrogen-, and sulfur-isotope signatures. Can. J. Zool. 80, 223. Dunton, K.H., Saupe, S.M., Golikov, A.N., Schell, D.M., Schonberg, S.V., 1989. Trophic relationships and isotopic gradients among arctic and subarctic marine fauna. Mar. Ecol. Prog. Ser. 56, 89–97. Hamade, A.K., 2014. Fish Consumption Advice for Alaskans: A Risk Management Strategy to Optimize the Public's Health. Alaska Scientific Advisory Committee for Fish Consumption. Section of Epidemiology. Division of Public Health, Department of Health and Social Services, State of Alaska, p. 78 (http://dhss.alaska.gov/dph/Epi/eph/ Documents/fish/FishConsumptionAdvice2014.pdf). Hilderbrand, G.V., Farley, S.D., Robbins, C.T., Hanley, T.A., Titus, K., Servheen, C., 1996. Use of stable isotopes to determine diets of living and extinct bears. Can. J. Zool. 74, 2080–2088. Hobson, K.A., Schell, D.M., 1998. Stable carbon and nitrogen isotope patterns in baleen from eastern Arctic bowhead whales (Balaena mysticetus). Can. J. Fish. Aquat. Sci. 55, 2601–2607. Hobson, K.A., Welsh, H.E., 1992. Determination of trophic relationships within a high Arctic marine food web using δ13C and δ15N analysis. Mar. Ecol. Prog. Ser. 84, 9–18. IPHC, 2012. International Pacific Halibut Commission Annual Report 2011. International Pacific Halibut Commission, Seattle, WA, USA. IPHC, 2015. International Pacific Halibut Commission Website (www.iphc.int). Julshamn, K., Frantzen, S., Valdersnes, S., Nilsen, B., Maage, A., Nedreaas, K., 2011. Concentrations of mercury, arsenic, cadmium and lead in Greenland halibut (Reinhardtius hippoglossoides) caught off the coast of northern Norway. Mar. Biol. Res. 7, 733–745. Kahle, D., Wickham, H., 2013. ggmap: spatial visualization with ggplot2. R Journal 5, 144–161. Keith, S., Kong, T., Sadorus, L., Stewart, I., Williams, G., 2014. The Pacific halibut: biology, fishery, and management. International Pacific Halibut Commission. Technical Report No. 59. Kelly, J.F., 2000. Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology. Can. J. Zool. 78, 1–27. Kjellström, T., 1991. Effects on early childhood development of prenatal exposure to methylmercury. Arch. Environ. Health 46, 118.

7

Kong, T.M., Gilroy, H.L., Leickly, R.C., 2004. Definition of IPHC statistical areas. International Pacific Halibut Commission. Technical Report No. 49. Kurle, C.M., Worthy, G.A.J., 2002. Stable nitrogen and carbon isotope ratios in multiple tissues of the northern fur seal Callorhinus ursinus: implications for dietary and migratory reconstructions. Mar. Ecol. Prog. Ser. 236, 289–300. Loher, T., 2008. Homing and summer feeding site fidelity of Pacific halibut (Hippoglossus stenolepis) in the Gulf of Alaska, established using satellite-transmitting archival tags. Fish. Res. 92, 63–69. Loher, T., Clark, W.G., 2010. Deployment, recovery, and reporting of pop-up archival transmitting (PAT) tags to study interannual dispersal and seasonal migration timing in IPHC regulatory area 4. In: Sadorus, L. (Ed.), Report of Assessment and Research Activities 2009. International Pacific Halibut Commission, Seattle, WA, USA, pp. 537–551. McKeown-Eyssen, G., Ruedy, J., Neims, A., 1983. Methylmercury exposure in northern Quebec. II: neurological findings in children. Am. J. Epidemiol. 118, 470–479. Myers, G.J., Davidson, P.W., Strain, J.J., 2007. Nutrient and methyl mercury exposure from consuming fish. J. Nutr. 137, 2805–2808. Naidu, A.S., Scalan, R.S., Feder, H.M., Goering, J.J., Hameedi, M.J., Parker, P.L., Behrens, E.W., Caughey, M.E., Jewett, S.C., 1993. Inner shelf transfer and recycling in the Bering and Chukchi seas stable organic carbon isotopes in sediments of the north Bering-south Chukchi seas, Alaskan-Soviet Arctic Shelf. Cont. Shelf Res. 13, 669–691. NOAA, 2015. FISHWATCH. U.S. Seafood Facts. Pond, C.M., Gilmour, I., 1997. Stable isotopes in adipose tissue fatty acids as indicators of diet in arctic foxes (Alopex lagopus). Proc. Nutr. Soc. 56, 1067–1081. Rea, L.D., Castellini, J.M., Correa, L., Fadely, B.S., O'Hara, T.M., 2013. Maternal Steller sea lion diets elevate fetal mercury concentrations in an area of population decline. Sci. Total Environ. 454–455, 277–282. Ricca, M.A., Miles, K.A., Anthony, R.G., 2008. Sources of organochlorine contaminants and mercury in seabirds from the Aleutian archipelago of Alaska: inferences from spatial and trophic variation. Sci. Total Environ. 406, 308–323. Rocque, D.A., Winker, K., 2004. Biomonitoring of contaminants in birds from two trophic levels in the North Pacific. Environ. Toxicol. Chem. 23, 759–766. Schell, D.M., Barnett, B.A., Vinette, K.A., 1998. Carbon and nitrogen isotope ratios in zooplankton of the Bering, Chukchi and Beaufort seas. Mar. Ecol. Prog. Ser. 162, 11–23. Stewart, P.W., Reihman, J., Lonky, E.I., Darvill, T.J., Pagano, J., 2003. Cognitive development in preschool children prenatally exposed to PCBs and MeHg. Neurotoxicol. Teratol. 25, 11–22. U.S. EPA, 2007. Method 7473, Mercury in solids and solutions by thermal decomposition, amalgamation, and atomic absorption spectrometry. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, SW-846. Environmental Protection Agency. Valero, J.L., Webster, R.A., 2012. Current understanding of Pacific halibut migration patterns. International Pacific Halibut Commission Report of Assessment and Research Activities. 2011, pp. 341–380. Wagemann, R., Trebacz, E., Hunt, R., Boila, G., 1997. Percent methylmercury and organic mercury in tissues of marine mammals and fish using different experimental and calculation methods. Environ. Toxicol. Chem. 16, 1859–1866. www.openstreetmap.org. Yang, M.-S., 1996. Diets of important groundfishes in the Aleutian Islands in summer 1991. NOAA Technical Memorandum NMFS-AFSC-60.

Please cite this article as: Bentzen, R., et al., Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.08.068