Bering Sea | Mammals
Higher proportion of predatory fish in the diet of adult female Steller sea lions west of Amchitka Pass, Alaska correlated with higher mercury in pups Presenter: Lorrie Rea , ldrea@alaska.edu, University of Alaska - Fairbanks Brian Taras , btaras@alum.mit.edu, Alaska Department of Fish and Game, retired; currently Solid Solutions, Fairbanks, AK Todd O’Hara , tmohara@tamu.edu, Texas A&M University The prevalence of Steller sea lion (SSL; Eumetopias jubatus ) pups with high total mercury concentrations ([THg]) in hair was greater on rookeries west of Amchitka Pass than to the east, while increasing from 2011 to 2019 at some locations. Natal hair (known as lanugo) is grown in utero. The winter diet of adult female SSL influences the [THg] in the lanugo of the developing fetus (some at concentrations of concern). The Bayesian stable isotope mixing model framework MixSIAR was used to estimate the dams’ winter diet based on δ13C and δ15N measured in their pup’s whisker segments grown during late gestation and the δ13C and δ15N measured in 14 marine fish and cephalopod species known to occur in SSL diets. Dams were grouped into low (L), moderate (M) and high (H) toxicological risk categories based on the [THg] in their pup’s lanugo. All top diet models (lowest DIC and LOOic) included year and risk category (L, M, H) when SSL were sampled either east or west of Amchitka Pass, between 2011-2015 or 2017-2019. Between 2011-2015 prey showed higher [THg] in the west region, with a higher proportion of predatory fish in the SSL diet to the west. The proportion of predatory prey in the diet increased with year during this period and was highest in females in the high-risk category (H) across the range. From 2017-2019, there was no significant difference in the [THg] of prey between east and west, but a greater proportion of predatory fish in the diet of females from the west region remained, similar to the earlier time period. Proportion of predatory prey was greatest in the diet of high-risk females in both east and west regions, although the effect of year within this time period was variable. In summary, a toxicologically important increase in the proportion of predatory prey in the diet of adult female SSL contributed significantly to the pattern of highest [THg] in pups to the west, and the temporal increase in pup [THg] over time in this region.
Alaska Marine Science Symposium 2023 266
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