Predatory fish consumption by adult female Steller sea lions is positively related to mercury contamination of pups.

Environmental mercury has been an increasing concern in Arctic marine ecosystems and biomagnifies in marine food webs to impact apex predators through chronic exposure. We utilized stable isotopes of carbon (δ13C) and nitrogen (δ15N) measured in the vibrissa (whiskers) of Steller sea lion (Eumetopias jubatus Schreber, 1776) pups and in the muscle tissue of 13 species of marine fish and cephalopods in Bayesian stable isotope mixing models to estimate prey composition of 658 adult female sea lions during late gestation (winter). Our objective was to determine if the proportional composition of the dam diet reflected in these pups were related to the total mercury concentration ([THg]) in the pups’ lanugo (natal hair), time period (2011–2015 vs. 2017–2019), and/or region (east vs. west of Amchitka Pass). There was no consistent pattern of change over time in [THg] of prey muscle tissue within predatory or non-predatory fish in the locations sampled in contrast to significant increase in lanugo [THg] found in Steller sea lion pups over this period. In both regions, adult females that gave birth to pups with higher lanugo [THg] consumed a greater proportion of predatory prey during late gestation foraging.