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

Regional variations and drivers of essential and non-essential elements in Steller sea lion pups from the Aleutian Islands, Alaska

Exposure and resulting tissue concentrations of various elements from natural and anthropogenic sources are influenced by multiple factors, such as geographic location, age, diet, and metabolic rate, that can influence wildlife health. Essential and non-essential elements were assessed in lanugo and whole blood collected in 2019 from 102 Steller sea lion (Eumetopias jubatus) pups from two rookeries from the western and central Aleutian Islands: Agattu (WAI, n = 54) and Ulak Islands (CAI, n = 48). Rookery, sex, dorsal standard length, and trophic ecology (ẟ15N, ẟ13C values) effects on element concentration were evaluated. Significant differences in element concentrations of lanugo were exhibited across rookeries (p < 0.05), except for zinc (Zn). For example, higher mercury (Hg) and selenium (Se) concentrations were observed in WAI than CAI, while other elements were lower in WAI. Whole blood showed higher sulfur (S) and Se concentrations in CAI compared to WAI, while WAI had elevated strontium (Sr) and Hg concentrations relative to CAI. Trophic ecology significantly influenced most element concentrations, possibly due to regional variations in adult female feeding and food web dynamics. Interactions between elements were found in lanugo across both rookeries, with varying strengths. Whole blood displayed less pronounced yet consistent associations, with variable intensities. Essential elements sodium (Na), potassium (K), and calcium (Ca) formed a distinct group whose interaction is crucial for nervous system function and muscle contraction. Another group comprised zinc (Zn), iron (Fe), manganese (Mn), magnesium (Mg), phosphorous (P), S, and Se, which are known for indirectly interacting with enzyme function and metabolic pathways. Hg and Se formed a distinct group probably due to their known chemical interactions and physiological protective interactions.

Mercury and stable nitrogen isotope ratios in the hair of bearded seals (Erignathus barbatus nauticus) from the Sea of Okhotsk

The mercury pollution status in the northwestern Sea of Okhotsk remains largely unexplored. In this study, hair samples were collected from 40 bearded seals harvested between August and October 2021 in the region. Total mercury (THg) concentrations in the samples exhibited a wide range from 137 to 1885 ng/g (median: 407 ng/g). While no significant differences in THg concentrations were found between male and female seals, distinctions were observed between young and potentially mature seals. Stable nitrogen isotope analysis indicated that juveniles and mature adults did not differ, although sample sizes were limiting. The higher THg concentrations in juveniles were attributed to variations in the seals' diets and/or variations in foraging locations during the juvenile stage which likely contribute to THg differences due to greater seasonal migration to offshore habitats. Notably, THg levels in bearded seals from the northwestern Sea of Okhotsk were lower in comparison to other pinniped species in the North Pacific. These findings, representing the first dataset for this pinniped species in the Russian segment of its habitat, contribute insights into mercury exposure in the Sea of Okhotsk mammalian population.

Spatial and cumulative organochlorine and mercury exposure assessments in Steller Sea lions of Alaska: Emphasizing pups

Steller sea lions (SSL) are sentinels for monitoring environmental contaminants in remote areas of the Aleutian Islands, Alaska. Therefore, concentrations of several organochlorines (OCs) were measured in blood from 123 SSL pups sampled from 3 regions; the western Aleutian Islands (WAI), central Aleutian Islands (CAI), and the central Gulf of Alaska. Blood, blubber, and milk from 12 adult female SSL from WAI, CAI and southeast Alaska also were analyzed. Findings included the following. SSL pups had higher concentrations of some OCs and mercury (Hg) on rookeries in the WAI than those more easterly. Pups had significantly higher blood concentrations of many OC classes than adult females sampled within the same region; some pups had PCB concentrations exceeding thresholds of concern (∑PCBs >8600 ng/g lw). ∑PCB concentration in pup whole blood was positively correlated with the trophic marker, δ15N within the regions sampled, along with two PCB congeners (PCB138 and PCB153). This suggests that the dams of pups with higher ∑PCBs, PCB138, and PCB153 concentrations were feeding on more predatory prey. Adult female blubber ∑DDT and hexachlorocyclohexane concentrations were also positively correlated with δ15N values. Several pups (mostly from WAI) had blood Hg concentrations and/or blood PCB concentrations (surrogate for overall OC exposures) of concern. The finding that WAI SSL pups have been exposed to multiple contaminants calls for future investigation of their cumulative exposure to a mixture of contaminants especially their transplacental and then transmammary exposure routes.

Total mercury concentrations in Steller sea lion bone: Variability among locations and elements

Mercury is a global contaminant that bioaccumulates in a tissue-specific manner in long-lived predators such as Steller sea lions (SSL). Bone is a well-preserved material amenable for studying millennial scale trends; however, little is known about the distribution and variability of total mercury concentrations ([THg]) within individual bones and among bone elements in SSL. We assessed SSL bone [THg] variability with respect to physiologic age, bone type, longitudinally within a bone, and among bone elements. Pup bones (mean ± SD; 31.4 ± 13.58 ppb) had greater [THg] than adults (7.9 ± 1.91 ppb). There were greater and more variable [THg] within individual long bones near epiphyses compared to mid-diaphysis. Pup spongy bone in ribs (62.7 ± 44.79 ppb) had greater [THg] than long bones (23.5 ± 8.83 ppb) and phalanges (19.6 ± 10.78 ppb). These differences are likely due to variability in bone composition, growth, and turnover rate. This study informs standardized sampling procedures for [THg] in bone to improve interpretations of mercury variability over time and space.

Compound-specific stable isotopes of amino acids reveal influences of trophic level and primary production sources on mercury concentrations in fishes from the Aleutian Islands, Alaska

Total mercury concentrations ([THg]) exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus) tissues from certain portions of the Aleutian Islands, Alaska. We applied compound-specific stable isotope analyses of both carbon and nitrogen in amino acids from fish muscle tissue to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of Steller sea lion diets. Previous THg analyses of fish muscle, coupled with monomethylmercury analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle Hg concentrations relative to fishes from the east. The δ13C values of essential amino acids (EAAs) in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this EAA source. The δ15N values of phenylalanine (0.9 to 7.8 ‰), an indicator of the isotopic baseline of a food web, varied widely within and among fish species. Trophic position estimates, accounting for this baseline variation, were higher from the west relative to the east of the pass for some fish species. Trophic magnification slopes using baseline-corrected trophic position estimates indicated similar rates of Hg biomagnification to the east and west of Amchitka Pass. Multiple linear regression models revealed that trophic position was the most important driver of fish muscle [THg] with less variation explained by other parameters. Thus, higher trophic positions but not the rate of Hg biomagnification to the west of Amchitka Pass may play a role in the regional differences in both fish and Steller sea lion [THg]. Although, differences in Hg contamination and uptake at the base of the east and west food webs could not be excluded.

Mercury and selenium concentrations in lanugo of free-ranging California sea lions in the southern Gulf of California, Mexico

Total mercury ([THg]) and selenium ([TSe]) concentrations were determined in California sea lion (Zalophus californianus) lanugo from the Gulf of California in 2021 and 2022. Relationships with sex, morphometrics, and year were evaluated. Following toxicological thresholds of concern for piscivorous mammals, most pups had a [THg] < 10 ppm, one pup (2021) had a [THg] > 20 ppm, no pups had a [THg] > 30 ppm. Females had significantly higher [TSe] than males; sex did not influence [THg]. [THg] and [TSe] in 2022 were significantly higher in the general population and male cohorts compared to 2021. Significant negative correlations were observed between [THg], [TSe], and morphometrics (2021). These results indicate that, compared to other pinniped species, regional California sea lions may have a decreased likelihood of experiencing Hg-related adverse health effects. Year-related changes in element concentrations suggest continued monitoring of this population to assess pinniped, environmental, and potentially, human health.

Fasting durations of Steller sea lion pups vary among subpopulations-evidence from two plasma metabolites

Geographic differences in population growth trends are well-documented in Steller sea lions (Eumetopias jubatus), a species of North Pacific pinniped listed under the U.S. Endangered Species Act in 1990 following a marked decline in population abundance that began during the 1970s. As population growth is intrinsically linked to pup production and survival, examining factors related to pup physiological condition provides useful information to management authorities regarding potential drivers of regional differences. During dam foraging trips, pups predictably transition among three fasting phases, distinguished by the changes in the predominant metabolic byproduct. We used standardized ranges of two plasma metabolites (blood urea nitrogen and β-hydroxybutyrate) to assign pups to fasting categories (n = 1528, 1990-2016, 12 subpopulations): Recently Fed-Phase I (digestion/assimilation-expected hepatic/muscle glycogen usage), Phase II (expected lipid utilization), transitioning between Phases II-III (expected lipid utilization with increased protein reliance), or Phase III (expected protein catabolism). As anticipated, the majority of pups were classified as Recently Fed-Phase I (overall mean proportion = 0.72) and few pups as Phase III (overall mean proportion = 0.04). By further comparing pups in Short (Recently Fed-Phase II) and Long (all other pups) duration fasts, we identified three subpopulations with significantly (P < 0.03) greater proportions of pups dependent upon endogenous sources of energy for extended periods, during a life stage of somatic growth and development: the 1) central (0.27 ± 0.09) and 2) western (0.36 ± 0.13) Aleutian Island (declining population trend) and 3) southern Southeast Alaska (0.32 ± 0.06; increasing population trend) subpopulations had greater Long fast proportions than the eastern Aleutian Islands (0.10 ± 0.05; stabilized population). Due to contrasting population growth trends among these highlighted subpopulations over the past 50+ years, both density-independent and density-dependent factors likely influence the dam foraging trip duration, contributing to longer fasting durations for pups at some rookeries.

Associations between urogenital carcinoma and DECA-BDE (BDE-209) among wild California Sea lions (Zalophus californianus) and Steller Sea lions (Eumetopias jubatus)

Urogenital carcinoma (UGC) is prevalent among California sea lions (Zalophus californianus), while less is known concerning UGC among Steller sea lions (Eumetopias jubatus). Our objective was to investigate associations between UGC and polybrominated diphenyl ethers (PBDEs) among both sea lion species. Twenty-nine California sea lions and 20 Steller sea lions were lethally removed from the Columbia River Basin, Oregon, USA between 2020 and 2021, under Section 120 of the Marine Mammal Protection Act. UGC was diagnosed through gross necropsy and histopathology. Forty PBDE congeners were analyzed in blubber, including BDE-209, a potential carcinogen. Twenty (69 %) California sea lions and one (5 %) Steller sea lion were diagnosed with UGC. All cases were identified as early stage UGC, aside from one California sea lion with more advanced stage UGC. Among California sea lions, associations between PBDEs and UGC were analyzed using logistic regression. In the adjusted model, BDE-209 (log2-transformed) was associated with increased odds of UGC [Odds Ratio (OR): 4.68, 95 % confidence interval: 1.04, 21.0, OR p-value = 0.044). This is the first study to report BDE-209 concentrations in sea lion blubber. The percentages of California and Steller sea lions diagnosed with UGC were higher than expected for wild (non-stranded) sea lions. Our results suggested blubber BDE-209 was potentially associated with UGC in California sea lions in the Columbia River Basin.

Mercury content in the fur of sea otters (Enhydra lutris) from the Commander Islands

The sea otter (Enhydra lutris) is a keystone species in the ecosystem which is currently in depression in Russia. The objectives of this study were to: (1) establish if the sea otters from the Commander Islands have hazardous levels of mercury (Hg) in their fur; (2) assess Hg pollution in sea otters during a period of high abundance and population depression; (3) identify the age and sex differences in sea otters by Hg content. The sea otters were classified from no to low risk for Hg health effects. Differences in Hg content during periods of low and high population size were not statistically significant. Hg concentrations in adult sea otters were significantly higher than in the young, and higher in males than in females. This study presents the first data on Hg content in sea otters' fur and the first estimate of Hg contamination for the Commander Islands population.

Whiskers provide time-series of toxic and essential trace elements, Se:Hg molar ratios, and stable isotope values of an apex Antarctic predator, the leopard seal

In an era of rapid environmental change and increasing human presence, researchers need efficient tools for tracking contaminants to monitor the health of Antarctic flora and fauna. Here, we examined the utility of leopard seal whiskers as a biomonitoring tool that reconstructs time-series of significant ecological and physiological biomarkers. Leopard seals (Hydrurga leptonyx) are a sentinel species in the Western Antarctic Peninsula due to their apex predator status and top-down effects on several Antarctic species. However, there are few data on their contaminant loads. We analyzed leopard seal whiskers (n = 18 individuals, n = 981 segments) collected during 2018-2019 field seasons to acquire longitudinal profiles of non-essential (Hg, Pb, and Cd) and essential (Se, Cu, and Zn) trace elements, stable isotope (ẟ15N and ẟ13C) values and to assess Hg risk with Se:Hg molar ratios. Whiskers provided between 46 and 286 cumulative days of growth with a mean ~ 125 days per whisker (n = 18). Adult whiskers showed variability in non-essential trace elements over time that could partly be explained by changes in diet. Whisker Hg levels were insufficient (<20 ppm) to consider most seals being at "high" risk for Hg toxicity. Nevertheless, maximum Hg concentrations observed in this study were greater than that of leopard seal hair measured two decades ago. However, variation in the Se:Hg molar ratios over time suggest that Se may detoxify Hg burden in leopard seals. Overall, we provide evidence that the analysis of leopard seal whiskers allows for the reconstruction of time-series ecological and physiological data and can be valuable for opportunistically monitoring the health of the leopard seal population and their Antarctic ecosystem during climate change.

Trace metal concentrations in California sea lions from rookeries exposed to different levels of coastal urbanization in Baja California, Mexico

Concentrations of total mercury, total selenium, and cadmium ([THg], [TSe], [Cd]) were determined in hair of California sea lion (Zalophus californianus) pups from four islands of the Gulf of California and the Baja California Pacific coast (NG, CG, NP, and CP) to identify geographical differences and the effect of Se against Hg toxicity (TSe:THg molar ratio). THg displayed a strong north-south trend for both ecoregions, while TSe presented a significantly high concentration only for CG. TSe:THg molar ratios decreased when [THg] increased, with the lowest ratios presenting in NG pups, in which [THg] exceeded toxicological thresholds of concern. [Cd] presented similar values at all study sites except CG, which presented the lowest level. The present study shows that proximity to urbanized coastal areas has a strong influence on [THg] in pups, while [TSe] and [Cd] are probably more related to the physiological requirements of the species, and environmental conditions.

EVALUATION OF TRACE ELEMENT CONCENTRATIONS IN THE SERUM AND VIBRISSAE OF PERUVIAN PINNIPEDS (ARCTOCEPHALUS AUSTRALIS AND OTARIA BYRONIA)

Concentrations of 15 trace elements (aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, selenium, tin, vanadium, and zinc) were determined in vibrissae (whiskers) and serum of two sympatric pinniped species, the Peruvian fur seal population (PFS; Arctocephalus australis Peruvian subpopulation) and South American sea lion (SASL; Otaria byronia) at Punta San Juan, Peru during 2011-19 sampling events. Element concentrations were 2-20 times higher in vibrissae than in serum. Vibrissae and serum concentrations of several elements, including aluminum, arsenic, and lead, suggest that environmental contaminants may affect the health of pinnipeds at Punta San Juan. Although toxicity thresholds are unknown in pinnipeds, high concentrations of some elements (especially aluminum, arsenic, and lead) may have adverse impacts on their health such as immunosuppression and impaired reproduction. Arsenic was the only element that increased in mean vibrissae concentration throughout the study period. Female SASL vibrissae contained a mean arsenic concentration three times higher than the male SASL vibrissae mean arsenic concentration, and twice as high as the arsenic mean for all PFS vibrissae. The mean male SASL vibrissae cadmium concentration was five times higher than the vibrissae cadmium mean for both PFS males and females and nearly three times higher than the vibrissae cadmium mean for SASL females. Serum concentrations of aluminum, arsenic, copper, and manganese were significantly higher during moderate to extreme El Niño years compared to La Niña years. With stronger and more frequent El Niño-Southern Oscillation events predicted in the future, it is vital to understand how these trace elements may affect pinniped population health.

Total Mercury, Total Selenium, and Monomethylmercury Relationships in Multiple Age Cohorts and Tissues of Steller Sea Lions (Eumetopias jubatus)

Steller sea lion (Eumetopias jubatus) tissue mercury concentrations increasingly above thresholds of concern occur in regions of Alaska where lack of population recovery is noted. Selenium-monomethylmercury interactions may mitigate toxicosis but may also result in functional selenium deficiency, impacting essential selenium-dependent processes. Physiologically driven differences in tissue concentrations (organotropism) of total mercury ([THg]), total selenium ([TSe]), and monomethylmercury ([MeHg⁺ ]) confound interpretation for various age cohorts. Archived tissues from Alaska Steller sea lions (2002-2016) were used to compare [THg], [MeHg⁺ ], and [TSe] across age cohorts and tissue types. Liver [THg] ranged from 0.05 to 63.7 µg/g. Fetal and pup livers had significantly lower [THg] and [TSe], higher percentage MeHg⁺ , and greater range of molar TSe:THg than subadult and adult livers. Molar Se:MeHg⁺ ratios, including Se in excess of nonmethylmercury, were dependent on [MeHg⁺ ] in fetuses and pups. While [THg] varied significantly by muscle type (heart vs. skeletal) and anatomical location, concentrations were strongly correlated. Biomagnification and/or bioaccumulation of THg in liver of older animals confounded comparison with other tissues; however, in fetal and pup liver [THg] correlated with other tissues. In contrast, liver [MeHg⁺ ] correlated with other tissues across all age classes. Fetal and pup tissues, which reflect in utero exposure and are subject to limited bioaccumulation, are ideal for assessing mercury exposure related to dam diet, including intertissue comparison, and represent key cohorts of concern. Evaluating [MeHg⁺ ] and [TSe] in tissues from multiple age cohorts allows better intertissue comparison, providing insight into time courses, routes of exposure, and potential for adverse effects. Environ Toxicol Chem 2022;41:1477-1489. © 2022 SETAC.

Regional variations and relationships among cytokine profiles, white blood cell counts, and blood mercury concentrations in Steller sea lion (Eumetopias jubatus) pups

The Steller sea lion (SSL) population west of 144°W longitude experienced a significant population decline. While there appears to be a stable or increasing population trend in rookeries in the Gulf of Alaska (GOA) and Southeast Alaska (SEA), some rookeries within the Aleutian Islands (AI) have failed to recover. Previous studies found regional differences in whole blood total mercury concentrations ([THg]) showing more than 20% of AI pups had [THg] above critical thresholds for increased risk of immunological effects and other adverse outcomes. Measurements of immune cell-signaling proteins can be used to evaluate the immune status of marine mammals in relation to [THg]. We compared serum cytokine and chemokine concentrations in pups among regions (AI, eastern GOA, SEA), and examined associations among cytokines, chemokines, white blood cell (WBC) counts, and [THg]. Considering liver is an important target organ for mercury and immune protein synthesis we additionally examined the relationship of [THg] with liver-related enzymes serum aspartate (AST) and alanine aminotransferase (ALT). We observed regional differences in cytokine and chemokine measurements and immune protein associations. There was a positive association between total WBC counts and [THg] in AI pups, whereas a negative association between lymphocytes and [THg] in SEA pups. These findings may indicate regional variation in proliferation and differentiation of hematopoietic cells, differences in immune system development, and/or a difference in antigenic stimuli. No associations between [THg] and cytokines, chemokines, AST or ALT were found. Observed regional differences in cytokine and chemokine milieu during gestational and early development in SSL pups could lead to an imbalance in cell differentiation that could impact immunological resiliency in juvenile and adult life stages. We report concentration ranges of a suite of cytokines and chemokines which may prove to be a useful metric for ecotoxicology and risk assessment studies in SSLs and other wildlife.

Biomonitoring mercury contamination using fur from roadkilled giant anteaters

The giant anteater (Myrmecophaga tridactyla) can occur in both preserved and anthropogenic environments in Brazilian biomes. The Cerrado biome, where the samples were collected, is considered one of the world's biodiversity hotspots; however, a large part of it has been converted to pasture and agricultural land. In this environment, animals may be exposed to contaminants, such as mercury (Hg). Despite its immense biodiversity, there are few studies investigating Hg contamination in terrestrial mammals in Brazil. This study aimed to create a baseline for Hg levels in giant anteater fur and establish which biotic and abiotic variables can influence its concentration. Total Hg (THg) concentrations were determined by cold vapor atomic absorption spectrometry in 141 individuals sampled on highways between January and October 2017, in the state of Mato Grosso do Sul, Brazil. THg concentrations in fur ranged from 0.27 to 4.77 μg g ^-1. The decomposition stage of the carcasses and vehicular traffic volume on highways did not influence the THg concentrations. Juveniles presented lower THg concentrations than adults. A spatial pattern of higher concentrations in the eastern-southeastern region of the state was found, which could be related to anthropogenic impacts; however, no clear links have been established. The THg concentrations in giant anteaters' fur seems higher than expected considering the trophic position of the species. Despite this, the range was in accordance with studies of other Brazilian terrestrial mammals and within safe threshold levels. This study indicates the potential of utilizing roadkilled fauna to monitor large-scale contamination in wildlife.

Regional variations and drivers of mercury and selenium concentrations in Steller sea lions

Mercury (Hg) can be neurotoxic to mammals and impact reproduction, whereas selenium (Se) is an important antioxidant known to ameliorate some adverse effects of Hg. Total Hg concentrations ([THg]) were measured in lanugo (pelage grown in utero) of 812 Steller sea lion (Eumetopias jubatus) pups across Alaska and Russia to assess fetal exposure during late gestation. The molar ratio of total Se to THg (TSe:THg) was determined in whole blood collected from 291 pups. Stable isotope ratios of carbon and nitrogen were measured in sections of vibrissae (whiskers, n = 498) and in lanugo (n = 480) of pups grown during late gestation to track diet variations among adult females that can drive Hg and Se exposure during this critical fetal development period. Lanugo [THg] ranged from 1.4 to 73.7 μg/g dry weight with the lowest median [THg] in Southeast Alaska. Pups from the Western Aleutian Islands had higher median lanugo [THg] than pups from other metapopulations in Alaska. Over 25% of pups in the Western Aleutian Islands had [THg] above published risk thresholds (20 μg/g) for other mammals. Whole blood molar TSe:THg was significantly lower in the Western Aleutian Islands and in some parts of the Central Aleutian Islands with higher molar ratios found in the Eastern Aleutian Islands and Central Gulf of Alaska. This suggests a limitation on potential protective functions of Se in the western regions with the highest relative [THg]. The Central Aleutian Island pups with [THg] over 20 μg/g had higher δ¹⁵N ratios than pups with lower [THg] suggesting dams consuming higher trophic level prey is a key driver for Hg exposure. However, regional differences likely reflect variability in diet of the dam during gestation and in Hg food web dynamics between oceanic regimes east and west of key passes in the Aleutian Islands.

Assessing oxidative stress in Steller sea lions (Eumetopias jubatus): Associations with mercury and selenium concentrations

Selenium (Se) bioavailability is required for synthesis and function of essential Se-dependent antioxidants, including the enzyme glutathione peroxidase (GPx). Strong interactions between monomethyl mercury and Se impair the critical antioxidant role of Se. Approximately 20% of Steller sea lion (Eumetopias jubatus, SSL) pups sampled in the western Aleutian Islands, Alaska, had total Hg concentrations ([THg]) measured in hair and whole blood above thresholds of concern for adverse physiologic effects in pinnipeds. Importantly, low molar ratios of TSe:THg, in some cases < 1 in several tissues (hair, liver, pelt, muscle, spleen, intestine, heart, lungs, brain) were documented for one SSL pup with [THg] above threshold of concern, which may lead to antioxidant deficiency. Our aim with this study was to evaluate the relationship between circulating [THg], [MeHg⁺], [TSe] and TSe:THg molar ratio status relative to oxidative stress and antioxidants measured during general anesthesia in free-ranging SSL. We captured, anesthetized and sampled newborn SSL pups at rookeries located in the Aleutian Islands or Gulf of Alaska. Biomarkers analyzed for oxidative stress included 4-hydroxynenonal and thiobarbituric acid reactive substances (4-HNE and TBARS, respectively, lipid peroxidation), protein carbonyl content (PCC, protein oxidation), and GPx activity as a key indicator for Se-dependent antioxidant defense levels. We found a negative association between TBARS and [TSe], and SSL with low [TSe] had higher concentrations of 4-HNE than those with intermediate [TSe]. These results suggest that SSL with lower [TSe] experience increased lipid peroxidation potentially associated with [THg] status.

Methyl mercury (MeHg) in vitro exposure alters mitogen-induced lymphocyte proliferation and cytokine expression in Steller sea lion (Eumetopias jubatus) pups

Steller sea lions (Eumetopias jubatus, SSLs) are managed as two distinct population segments within U.S. waters: the endangered western distinct population segment and the recently delisted eastern distinct population segment. Recent studies reported concentrations of mercury in several tissues collected from young SSLs in the Aleutian Islands that were at or above concentrations found to negatively impact health in other fish-eating mammals. However, there are limited studies which have investigated the range of mercury concentrations that may negatively influence the SSL immune system. This study assessed relationships between methyl mercury (MeHg⁺) concentrations and two immune functions, lymphocyte proliferation and cytokine expression. Peripheral blood mononuclear cells (PBMCs) were isolated and cryopreserved from pups on three rookeries within the western distinct population segment: Chiswell Island, Ulak, and Agattu Islands. Lymphocyte proliferation and cytokine expression were assessed in vitro using thawed PBMCs with exposure to MeHg⁺ (unexposed control, 0.001, 0.01, and 0.1 μg/ml). Lymphocyte proliferation was measured without and with stimulation with a T cell mitogen (ConA) and B cell mitogen (LPS) and the concentration of cytokines was measured in the cell culture supernatant (with and without ConA or LPS). Spontaneous lymphocyte proliferation was significantly increased at 0.01 and 0.1 μg/ml. T lymphocyte proliferation was significantly increased at 0.001 μg/ml and 0.1 μg/ml, while B lymphocyte proliferation was decreased at 0.1 μg/ml. Cytokine concentrations for INFγ, IL-10, IL-6, and TNFα were reduced at 0.1 μg/ml upon either T or B cell mitogen stimulation, with the exception for IL-10, where 0.1 μg/ml reduced IL-10 concentration compared to unstimulated cells. These data suggest immune functions were affected by MeHg⁺ exposure requiring in vivo follow up investigations. The observed modulation of immune functions is of concern as any toxicant-induced modulation may adversely affect the health of individuals, particularly younger animals undergoing periods of critical development.

Stress-related and reproductive hormones in hair from three north Pacific otariid species: Steller sea lions, California sea lions and northern fur seals

Assessing the physiological impact of stressors in pinnipeds is logistically challenging, and many hormones are altered by capture and handling, limiting the utility of metabolically active tissues. Hair is increasingly being used to investigate stress-related and reproductive hormones in wildlife populations due to less-invasive collection methods, being metabolically inert once grown and containing multiple biomarkers of ecological interest. We validated enzyme immunoassays for measuring aldosterone, cortisol, corticosterone, and testosterone in lanugo (natal hair grown in utero) samples collected from Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), and northern fur seals (Callorhinus ursinus). We applied laboratory validation methods including recovery of added mass, parallelism and dilution linearity. We found no effects due to differences in alcohol- versus detergent-based cleaning methods. Further, there were no significant differences in hormone concentrations in hair samples collected immediately after the molt and the subsequent samples collected over 1 year, indicating steroid hormones are stable once deposited into pinniped hair. We found no sex differences in any hormone concentrations, likely due to the lanugo being grown in utero and influenced by maternal hormone concentrations. For Steller sea lion and California sea lion pups, we found hormone concentrations significantly differed between rookeries, which warrants future research. Hair provides a novel tissue to explore the intrinsic or extrinsic drivers behind hormone measurements in otariids, which can be paired with multiple health-related metrics to further investigate possible drivers of physiological stress.

Selenium and mercury in the hair of raccoons (Procyon lotor) and European wildcats (Felis s. silvestris) from Germany and Luxembourg

This study examined the concentration of total mercury (THg) and selenium (Se), as well as the molar ratio of Se:THg in hair samples of terrestrial animals. THg and Se concentrations were measured from the hair of raccoons (Procyon lotor) and European wildcats (Felis s. silvestris) from Germany and Luxembourg. Median THg concentrations in hair from raccoons and wildcats were 0.369 and 0.273 mg kg-1 dry weight (dw), respectively. Se concentrations were higher in the hair of raccoons than of wildcats (0.851 and 0.641 mg kg-1 dw, respectively). Total mercury concentration in hair of raccoons from Luxembourg was almost 5× higher that found in hair of raccoons from Germany; however, Se concentration was similar. Thus, molar ratio of Se:THg was ~4× higher in the hair of raccoons from Germany than those from Luxembourg. Significant negative correlation was found between THg concentration and Se:THg molar ratio in both wildcats and raccoons.

Changes in total mercury, methylmercury, and selenium blood levels during different life history stages of the Baltic grey seal (Halichoerus grypus grypus)

Using the blood of grey seal pups, the blood and milk of female grey seals inhabiting the Hel Marine Station of Gdansk University's Institute of Oceanography (HMS), we monitored the transfer of total mercury (THg), methylmercury (MeHg), and selenium (Se) with blood during foetal life and nursing. Changes in the concentration of mercury and selenium were characterised in the pups' blood during their first three months of life when they transition from suckling, to a post-weaning fast, to eating fish. In the blood of pregnant females, there was a significant decrease in THg and MeHg concentrations throughout the gestation, indicating the transfer of these toxins through the placenta into the foetus. At no other stage of the pup's development was there such a high level of THg and MeHg as on the day of birth, despite the incorporation of mercury into the lanugo during foetal growth. This suggests that the maternal transfer of mercury during gestation may be the time of greatest mercury exposure for a young seal pup. The consumption of milk caused a rapid increase in weight and a lowering of the mercury level in the blood in the subsequent days of the pups' life. The postweaning fast was the period of the lowest mercury concentration. The switch to a diet consisting of fish caused a systematic increase in the concentration of mercury in the blood of the pups. Milk was the significant source of selenium for pups and the selenium concentration in females' blood was reduced during lactation. The nursing period seemed to have the greatest impact on the mercury and selenium blood levels in examined seals. Natural development of the grey seal pup created an opportunity to decrease the levels of toxic substances obtained through the maternal transfer during foetal growth.

Antarctophthirus microchir infestation in synanthropic South American sea lion (Otaria flavescens) males diagnosed by a novel non-invasive method

Antarctophthirus microchir is a sucking louse species belonging to the family Echinophthiriidae and has been reported to parasitize all species of the subfamily Otariinae, the sea lions. Former studies on this ectoparasite mainly required fixation, immobilization, or death of host species and especially examinations of adult male sea lions are still very rare. Between March and May 2018, adult individuals of a unique “urban” bachelor group of South American sea lions (Otaria flavescens) living directly in the city of Valdivia, Chile, were studied regarding their ectoparasite infestation status. For first time, a non-invasive method in the form of a lice comb screwed on a telescopic rod and grounded with adhesive tape was used for sample taking process. Overall, during combing different stages of A. microchir were detected in 4/5 O. flavescens individuals, especially at the junction between the back and hind flippers. Our findings represent the first report of A. microchir infesting individuals of this synanthropic colony and fulfilling complete life cycle in a sea lion group despite inhabiting freshwater and in absence of females/pups. Our “telescopic lice comb apparatus” offers a new strategy to collect different stages of ectoparasites and a range of epidermal material, such as fur coat hair and superficial skin tissue for a broad spectrum of research fields in wildlife sciences in an unmolested and stress reduced manner.

Mercury and lead exposure in avian scavengers from the Pacific Northwest suggest risks to California condors: Implications for reintroduction and recovery

Mercury (Hg) and lead (Pb) are widespread contaminants that pose risks to avian scavengers. In fact, Pb exposure is the primary factor limiting population recovery in the endangered California condor (Gymnogyps californianus) and Hg can impair avian reproduction at environmentally relevant exposures. The Pacific Northwest region of the US was historically part of the condor's native range, and efforts are underway to expand recovery into this area. To identify potential threats to reintroduced condors we assessed foraging habitats, Hg and Pb exposure, and physiological responses in two surrogate avian scavenger species (common ravens [Corvus corax] and turkey vultures [Cathartes aura] across the region between 2012 and 2016. Mercury exposure near the Pacific coast was 17-27-fold higher than in inland areas, and stable carbon and sulfur isotopes ratios indicated that coastal scavengers were highly reliant on marine prey. In contrast, Pb concentrations were uniformly elevated across the region, with 18% of the birds exposed to subclinical poisoning levels. Elevated Pb concentrations were associated with lower delta-aminolevulinic acid dehydratase (δ-ALAD) activity, and in ravens there was an interactive effect between Hg and Pb on fecal corticosterone concentrations. This interaction indicated that the effects of Hg and Pb exposure on the stress axis are bidirectional, and depend on the magnitude of simultaneous exposure to the other contaminant. Our results suggest that condors released to the Pacific Northwest may be exposed to both elevated Hg and Pb, posing challenges to management of future condor populations in the Pacific Northwest. Developing a robust monitoring program for reintroduced condors and surrogate scavengers will help both better understand the drivers of exposure and predict the likelihood of impaired health. These findings provide a strong foundation for such an effort, providing resource managers with valuable information to help mitigate potential risks.

Hair mercury concentrations in the spotted seal (Phoca largha) pups from the Sea of Japan

This publication presents the results of a study of the total mercury (THg) concentration in the fetal hair (lanugo) of the young spotted seals inhabiting the Peter the Great Bay, Sea of Japan. We analyzed samples from pups that were collected in 2014-2017 at the seal breeding grounds. The concentration of total mercury was determined by atomic absorption spectrometry. The concentration of THg ranged from 1.52 to 6.68 μg/g dry weight. Mercury concentration in the lanugo exceeds that found in the environment (bottom sediments, sea water) and in other animals inhabiting the Bay. At the same time, the level was generally lower than that found in young seals of most other pinniped species (Steller sea lion Eumetopias jubatus, Northern fur seal Callorhinus ursinus, Harbor seal Phoca vitulina richardsi, Northern elephant seal Mirounga angustirostris, California sea lion Zalophus californianus) from the North Pacific.

High status of mercury and selenium in false killer whales (Pseudorca crassidens, Owen 1846) stranded on Southern South America: A possible toxicological concern?

The study was carried out to determine Hg and Se concentrations in false killer whales stranded on the Estrecho de Magallanes, Chile, South America. Tissue samples of five mature specimens were analyzed (two females and three males). Mean Hg concentration in liver 1068 (234) μg g^-1 dry weight (DW) (standard deviation in parenthesis) was markedly higher than those in kidney 272 (152) μg g^-1 DW, lung 423 (325) μg g^-1 DW, spleen 725 (696) μg g^-1 DW, muscle 118 (94) μg g^-1 DW and testicle 18.0 (2.8) μg g^-1 DW. Mean Se concentration in liver, 398 (75) μg g^-1 DW, was higher than those in kidney 162 (69) μg g^-1 DW, lung 128 (84) μg g^-1 DW, spleen 268 (245) μg g^-1 DW, muscle 47 (38) μg g^-1 DW and testicle 25.4 (2.1) μg g^-1 DW. Positive correlations were found between Hg and Se molar concentrations in muscle, lung, spleen and kidney. Molar ratio of Se/Hg in liver, lung and muscle were <1, but those in kidney and testicle were markedly >1 suggesting a Se protection against Hg toxicity. In all the examined specimens Hg values exceeded the toxic thresholds defined for hepatic damage in marine mammals, with Se/Hg molar ratios below 1 implying limited protective action of Se. Generally, our results showed that individuals are carrying a significant burden, reflecting a high exposure to this toxic metal. This constitutes the first report on Hg and Se levels for a large subantarctic odontocete in South America region, providing insights into their contamination status and with information to the understanding of possible impacts on wild populations.

Long-Term and Ontogenetic Patterns of Heavy Metal Contamination in Lake Baikal Seals (Pusa sibirica)

Little is known about the history of heavy metal pollution of Russia's Lake Baikal, one of the world's largest lakes and a home to numerous endemic species, including the Baikal Seal, Pusa sibirica. We investigated the history of heavy metal (V, Cu, Zn, Cd, Hg, Tl, Pb, U) pollution in Lake Baikal seals over the past 8 decades. C and N stable isotope analysis (SIA) and laser-ablation ICP-MS of seal teeth were used to examine changes in feeding ecology, heavy metal levels associated with life history events and long-term variation in metal exposure. SIA did not suggest large changes in the feeding ecology of Baikal seals over the past 80 years. LA-ICP-MS analyses revealed element-specific ontogenetic variability in metal concentrations, likely related to maternal transfer, changes in food sources and starvation. Hg and Cd levels in seals varied significantly across the time series, with concentrations peaking in the 1960s - 1970s but then declining to contemporary levels similar to those observed in the 1930s and 1940s. Trends in atmospheric emissions of Hg suggest that local sources as well as emissions from eastern Russia and Europe may be important contributors of Hg to Lake Baikal and that, despite the size of Lake Baikal, its food web appears to respond rapidly to changing inputs of contaminants.

Contamination status and accumulation characteristics of heavy metals and arsenic in five seabird species from the central Bering Sea

Seabirds are marine top predators and accumulate high levels of metals and metalloids in their tissues. Contamination by metals in the highly productive offshore region has become a matter of public concern. It is home to 80% of the seabird population in the U.S.A., 95% of northern fur seals (Callorhinus ursinus), and major populations of Steller sea lions (Eumetopias jubatus), walruses (Odobenus rosmarus) and whales. Here, the concentrations of eight heavy metals (Hg, Cd, Cr, Co, Ni, Cu, Zn and Pb) and a metalloid (As) in the liver and kidneys of the northern fulmar (Fulmarus glacialis), thick-billed murre (Uria lomvia), short-tailed shearwater (Puffinus tenuirostris), tufted puffin (Fratercula cirrhata) and horned puffin (Fratercula corniculata) collected in the Bering Sea were measured. As proxies of trophic level and habitat, nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope ratios of breast muscles were also measured. Hepatic Hg concentration was high in northern fulmar, whereas Cd level was high in tufted puffin and northern fulmar. The Hg concentration and δ¹⁵N value were positively correlated across individual birds, suggesting that Hg uptake was linked to the trophic status of consumed prey. Furthermore, Hg concentration in our study was higher than those of the same species of seabirds collected in 1990.

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

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.

Mercury correlations among blood, muscle, and hair of northern elephant seals during the breeding and molting fasts

Mercury (Hg) biomonitoring and toxicological risk assessments for marine mammals commonly sample different tissues, making comparisons with toxicity benchmarks and among species and regions difficult. Few studies have examined how life-history events, such as fasting, influence the relationship between total Hg (THg) concentrations in different tissues. The authors evaluated the relationships between THg concentrations in blood, muscle, and hair of female and male northern elephant seals (Mirounga angustirostris) at the start and end of the breeding and molting fasts. The relationships between tissues varied among tissue pairs and differed by sampling period and sex. Blood and muscle were generally related at all time periods; however, hair, an inert tissue, did not strongly represent the metabolically active tissues (blood and muscle) at all times of year. The strongest relationships between THg concentrations in hair and those in blood or muscle were observed during periods of active hair growth (end of the molting period) or during time periods when internal body conditions were similar to those when the hair was grown (end of the breeding fast). The results indicate that THg concentrations in blood or muscle can be translated to the other tissue type using the equations developed but that THg concentrations in hair were generally a poor index of internal THg concentrations except during the end of fasting periods. Environ Toxicol Chem 2016;35:2103-2110. © 2016 SETAC.

Effects of Age, Colony, and Sex on Mercury Concentrations in California Sea Lions

We measured total mercury (THg) concentrations in California sea lions (Zalophus californianus) and examined how concentrations varied with age class, colony, and sex. Because Hg exposure is primarily via diet, we used nitrogen (δ (15)N) and carbon (δ (13)C) stable isotopes to determine if intraspecific differences in THg concentrations could be explained by feeding ecology. Blood and hair were collected from 21 adult females and 57 juveniles from three colonies in central and southern California (San Nicolas, San Miguel, and Año Nuevo Islands). Total Hg concentrations ranged from 0.01 to 0.31 μg g(-1) wet weight (ww) in blood and 0.74 to 21.00 μg g(-1) dry weight (dw) in hair. Adult females had greater mean THg concentrations than juveniles in blood (0.15 vs. 0.03 μg(-1) ww) and hair (10.10 vs. 3.25 μg(-1) dw). Age class differences in THg concentrations did not appear to be driven by trophic level or habitat type because there were no differences in δ (15)N or δ (13)C values between adults and juveniles. Total Hg concentrations in adult females were 54 % (blood) and 24 % (hair) greater in females from San Miguel than females from San Nicolas Island, which may have been because sea lions from the two islands foraged in different areas. For juveniles, we detected some differences in THg concentrations with colony and sex, although these were likely due to sampling effects and not ecological differences. Overall, THg concentrations in California sea lions were within the range documented for other marine mammals and were generally below toxicity benchmarks for fish-eating wildlife.

Evaluating Hair as a Predictor of Blood Mercury: The Influence of Ontogenetic Phase and Life History in Pinnipeds

Mercury (Hg) biomonitoring of pinnipeds increasingly utilizes nonlethally collected tissues such as hair and blood. The relationship between total Hg concentrations ([THg]) in these tissues is not well understood for marine mammals, but it can be important for interpretation of tissue concentrations with respect to ecotoxicology and biomonitoring. We examined [THg] in blood and hair in multiple age classes of four pinniped species. For each species, we used paired blood and hair samples to quantify the ability of [THg] in hair to predict [THg] in blood at the time of sampling and examined the influence of varying ontogenetic phases and life history of the sampled animals. Overall, we found that the relationship between [THg] in hair and blood was affected by factors including age class, weaning status, growth, and the time difference between hair growth and sample collection. Hair [THg] was moderately to strongly predictive of current blood [THg] for adult female Steller sea lions (Eumetopias jubatus), adult female California sea lions (Zalophus californianus), and adult harbor seals (Phoca vitulina), whereas hair [THg] was poorly predictive or not predictive (different times of year) of blood [THg] for adult northern elephant seals (Mirounga angustirostris). Within species, except for very young pups, hair [THg] was a weaker predictor of blood [THg] for prereproductive animals than for adults likely due to growth, variability in foraging behavior, and transitions between ontogenetic phases. Our results indicate that the relationship between hair [THg] and blood [THg] in pinnipeds is variable and that ontogenetic phase and life history should be considered when interpreting [THg] in these tissues.

Blood and Hair Mercury Concentrations in the Pacific Harbor Seal (Phoca vitulina richardii) Pup: Associations with Neurodevelopmental Outcomes

Monomethylmercury (MeHg(+)) is an environmental pollutant, which at sufficiently high exposures, has induced neurotoxicosis in several animal species, including humans. Adverse neurological effects due to gestational exposure are of particular concern as MeHg(+) readily crosses the blood-brain and placental barriers. The degree to which environmental concentrations in marine prey affect free-living piscivorous wildlife, however, remains largely undetermined. We examined associations of gestational exposures to mercury on neurodevelopment and survival using hair and blood concentrations of total mercury ([THg]) in a stranded population of Pacific harbor seal pups from central California. A positive association was determined for the presence of abnormal neurological symptoms and increasing [THg] in blood (P = 0.04), but not hair. Neither hair nor blood [THg] was significantly associated with survival, or the neurodevelopmental milestone 'free-feeding', which was measured from the onset of hand-assisted feeding to the time at which pups were able to consume fish independently. Both hair and blood [THg] exceeded threshold values considered potentially toxic to humans and other mammalian wildlife species. The higher [THg] in blood associated with abnormal neurological symptoms may indicate an adverse effect of this pollutant on neurodevelopment in harbor seal pups. These data have broader implications with respect to human health and public policy as harbor seals and humans consume similar fish species, and it is possible that safeguard levels established for marine mammals could also extend to human populations that regularly consume fish.

Hair and bone as predictors of tissular mercury concentration in the western Alaska red fox, Vulpes vulpes

We evaluated if total mercury (THg) concentrations of keratin-based and bone-based tissues can predict THg concentrations in skeletal muscle, renal medulla, renal cortex, and liver. The THg concentration in matched tissues of 65 red foxes, Vulpes vulpes, from western Alaska was determined. Hair THg concentration had a significant positive correlation with liver, renal medulla, renal cortex, and muscle. The THg concentration for males and females is moderately predictive of THg concentration in the renal cortex and liver for these foxes based on R(2) values (R(2)=0.61 and 0.63, respectively). Bone is weakly predictive of THg concentration in muscle (R(2)=0.40), but not a reliable tissue to predict THg concentration in liver (R(2)=0.24), renal cortex (R(2)=0.35), or renal medulla (R(2)=0.25). These results confirm the potential use of trapped animals, specifically foxes, as useful Arctic sentinel species to inform researchers about patterns in THg levels over time as industrialization of the Arctic continues.

Marine diet and tobacco exposure affects mercury concentrations in pregnant women (I) from Baja California Sur, Mexico

Seafood provides essential polyunsaturated fatty acids (PUFA) and other nutrients to pregnant women and their fetus(es) while a diet rich in finfish can be a major pathway of monomethyl mercury (MeHg⁺) exposure. We measured total mercury concentration ([THg]) in hair samples provided by 75 women in Baja California Sur (BCS) to assess its relationship with age, parity, tobacco smoke exposure, and diet based on survey methodologies. Generalized linear models (GLM) were used to explain the possible association of the different variables with [THg] in hair. Median [THg] in hair was 1.52 µgg^-1, ranging from 0.12 to 24.19 µgg^-1 and varied significantly by segment. Approximately 72% (54/75) of those evaluated exceed 1 µgg^-1 [THg] and 8% (6/75) exceed 5 µgg^-1 [THg] in hair. Although frequency of fish consumption contributed significantly to explaining hair [THg], fish consumption only explained 43% of [THg] in a GLM incorporating tobacco exposure and body mass index. This study establishes possible relationships among multiple potential sources of exposure and other factors related to [THg] in hair of women in the prenatal period. A more detailed examination of other sources of exposure and factors contributing to [THg] is warranted.

Relationship between self-reported fish and shellfish consumption, carbon and nitrogen stable isotope values and total mercury concentrations in pregnant women (II) from Baja California Sur, Mexico

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[THg], δ¹³C, and δ¹⁵N were measured in hair segments of pregnant women from Mexico.

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Higher δ¹⁵N was related to [THg] and frequency of fish and shellfish consumption.

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THg exposure and assimilation are more complex in higher fish consumption categories.

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At high fish consumption, trophic level remains elevated while [THg] is lower.

Seafood is a valuable source of nutrients important for fetal development. However, seafood consumption is the main route of exposure to monomethyl mercury (MeHg⁺) for humans. MeHg⁺ is highly bioavailable and potentially adversely affects fetal neurodevelopment. MeHg⁺ exposure from fish consumption varies significantly by age and trophic level of fish consumed as well as the frequency and amount of fish consumed. This study investigates total Hg concentrations ([THg]) in hair segments of pregnant Mexican women in relation to (1) self-reported frequency of fish and shellfish consumption, (2) maternal trophic level and marine diet contributions, determined using hair carbon (C) and nitrogen (N) stable isotopes, and (3) relates [THg] to various hair advisory thresholds. We also examined whether variation in C and N isotope values is explained by self-reported frequency of fish and shellfish consumption. A significant proportion of hair samples had [THg] higher than suggested agency thresholds and, for women within the range of the various advisory thresholds (1–20 μg g⁻¹), the specific statistic used and threshold applied are important considerations for assessing and communicating risk. Individuals enriched in ¹⁵N (δ¹⁵N values) had higher [THg] as did individuals that reported consuming fish and shellfish more frequently, suggesting that variation in [THg] can be explained by both consumer reported diet and diet as determined by C and N stable isotope assessment. However, at higher reported fish consumption levels the trophic level is maintained while [THg] is paradoxically lower. This suggests that THg exposure and assimilation are more complicated in higher fish frequency consumption categories. [THg] is more variable at the higher concentrations, possibly indicating some exposure to non-dietary Hg, heritable variations affecting Hg toxicodynamics, and BMI and tobacco exposure factors as outlined in our companion paper.

Selenium and mercury concentrations in harbor seals (Phoca vitulina) from central California: health implications in an urbanized estuary

We measured total selenium and total mercury concentrations ([TSe] and [THg]) in hair (n=138) and blood (n=73) of harbor seals (Phoca vitulina) from California to assess variation by geography and sex, and inferred feeding relationships based on carbon, nitrogen, and sulfur stable isotopes. Harbor seals from Hg-contaminated sites had significantly greater [THg], and lesser [TSe] and TSe:THg molar ratios than seals from a relatively uncontaminated site. Males had significantly greater [THg] than females at all locations. Sulfur stable isotope values explained approximately 25% of the variability in [THg], indicating increased Hg exposure for seals with a greater use of estuarine prey species. Decreased [TSe] in harbor seals from Hg-contaminated regions may indicate a relative Se deficiency to mitigate the toxic effects of Hg. Further investigation into the Se status and the potential negative impact of Hg on harbor seals from Hg-contaminated sites is warranted.

Assessment of mercury and selenium tissular concentrations and total mercury body burden in 6 Steller sea lion pups from the Aleutian Islands

Concentrations of total mercury ([THg]) and selenium ([TSe]) were measured in several tissue compartments in Steller sea lion (Eumetopias jubatus) pups; in addition we determined specific compartment and body burdens of THg. Compartmental and body burdens were calculated by multiplying specific compartment fresh weight by the [THg] (summing compartment burdens equals body burden). In all 6 pup tissue sets (1) highest [THg] was in hair, (2) lowest [THg] was in bone, and (3) pelt, muscle and liver burdens contributed the top three highest percentages of THg body burden. In 5 of 6 pups the Se:Hg molar ratios among compartments ranged from 0.9 to 43.0. The pup with the highest hair [THg] had Se:Hg molar ratios in 9 of 14 compartments that were ⩽ 0.7 potentially indicating an inadequate [TSe] relative to [THg].

Serum chemistry reference ranges for Steller sea lion (Eumetopias jubatus) pups from Alaska: stock differentiation and comparisons within a North Pacific sentinel species

Blood chemistry and hematologic reference ranges are useful for population health assessment and establishing a baseline for future comparisons in the event of ecosystem changes due to natural or anthropogenic factors. The objectives of this study were to determine if there was any population spatial structure for blood variables of Steller sea lion (Eumetopias jubatus), an established sentinel species, and to report reference ranges for appropriate populations using standardized analyses. In addition to comparing reference ranges between populations with contrasting abundance trends, data were examined for evidence of disease or nutritional stress. From 1998 to 2011, blood samples were collected from 1,231 pups captured on 37 rookeries across their Alaskan range. Reference ranges are reported separately for the western and eastern distinct population segments (DPS) of Steller sea lion after cluster analysis and discriminant function analysis (DFA) supported underlying stock structure. Variables with greater loading scores for the DFA (creatinine, total protein, calcium, albumin, cholesterol, and alkaline phosphatase) also were greater for sea lions from the endangered western DPS, supporting previous studies that indicated pup condition in the west was not compromised during the first month postpartum. Differences between population segments were likely a result of ecological, physiological, or age related differences.

Maternal Steller sea lion diets elevate fetal mercury concentrations in an area of population decline

Total mercury concentrations ([THg]) measured in western Aleutian Island Steller sea lion pup hair were the highest maximum [THg] documented in this endangered species to date. Some pups exceeded concentrations at which other fish-eating mammals can exhibit adverse neurological and reproductive effects (21% and 15% pups above 20 and 30 μg/g in hair, respectively). Of particular concern is fetal exposure to mercury during a particularly vulnerable stage of neurological development in late gestation. Hair and blood [THg] were highly correlated and 20% of pups sampled in the western Aleutian Islands of Alaska exceeded mammalian risk thresholds established for each of these tissues. Higher nitrogen isotope ratios suggested that pups accumulated the highest [THg] when their dams fed on higher trophic level prey during late gestation.

Correlates between feeding ecology and mercury levels in historical and modern arctic foxes (Vulpes lagopus)

Changes in concentration of pollutants and pathogen distribution can vary among ecotypes (e.g. marine versus terrestrial food resources). This may have important implications for the animals that reside within them. We examined 1) canid pathogen presence in an endangered arctic fox (Vulpes lagopus) population and 2) relative total mercury (THg) level as a function of ecotype (‘coastal’ or ‘inland’) for arctic foxes to test whether the presence of pathogens or heavy metal concentration correlate with population health. The Bering Sea populations on Bering and Mednyi Islands were compared to Icelandic arctic fox populations with respect to inland and coastal ecotypes. Serological and DNA based pathogen screening techniques were used to examine arctic foxes for pathogens. THg was measured by atomic absorption spectrometry from hair samples of historical and modern collected arctic foxes and samples from their prey species (hair and internal organs). Presence of pathogens did not correlate with population decline from Mednyi Island. However, THg concentration correlated strongly with ecotype and was reflected in the THg concentrations detected in available food sources in each ecotype. The highest concentration of THg was found in ecotypes where foxes depended on marine vertebrates for food. Exclusively inland ecotypes had low THg concentrations. The results suggest that absolute exposure to heavy metals may be less important than the feeding ecology and feeding opportunities of top predators such as arctic foxes which may in turn influence population health and stability. A higher risk to wildlife of heavy metal exposure correlates with feeding strategies that rely primarily on a marine based diet.

Hair sampling location in harbor seals (Phoca vitulina) affects selenium and mercury concentrations: implications for study design of trace element determination in pinnipeds

Hair is used to determine trace elements exposure and status of pinnipeds because it is an excretory route for many elements and can be collected non-lethally. Despite increased use, there have been few studies on how sampling designs and procedures (e.g., hair type, collection site) affect results. The objective of this study was to determine whether concentrations of an essential (selenium; Se) and non-essential element (mercury; Hg) differed between hair samples collected from two body locations on harbor seals (Phoca vitulina). Concentrations of Se and total Hg (THg) differed between mid-dorsal midline and neck samples, and although the absolute differences were relatively small (Δ(absolute) Se = 0.69 μg g(-1), Δ(absolute) THg = 2.86 μg g(-1)), the relative differences were large (Δ(relative) Se = 49%, Δ(relative) THg = 17%). These differences highlight the need to standardize the collection site for trace element determination in pinnipeds.