Bering Sea | Mammals
Too big to ignore: Foraging ecology and mercury concentrations of male Steller sea lions from the Aleutian Islands Presenter: Amy Bishop , ambishop2@alaska.edu, University of Alaska Anchorage Lorrie Rea , ldrea@alaska.edu, University of Alaska - Fairbanks Adult male Steller sea lions ( Eumetopias jubatus ) are the largest pinnipeds, growing in length for a longer period of time than females, and exhibiting growth spurts in mass coinciding with sexual maturity. With this size comes the potential to have significant impacts on marine food webs and ecosystems. Limited studies from scat have suggested males and females may have dietary differences, and bycatch rates tend to be higher for males. However, foraging studies for this species in Alaska typically do not differentiate across sexes or focus only on adult females and juveniles. The aim of this study was to begin to fill in these knowledge gaps by (1) characterizing the isotopic foraging niches of adult male Steller sea lions in the Aleutian Islands and southern Bering Sea and (2) identifying male foraging strategies associated with greater exposure to total mercury concentrations ([THg]), a contaminant of concern in the region. Vibrissae collected from males bycaught in commercial fisheries from 1998-2016 were sectioned every 0.5cm, and sequential segments were analyzed for bulk stable isotope ratios (δ15 N and δ13 C) and [THg]. Individuals exhibited regular temporal oscillations in both δ15 N and δ13 C that, based on vibrissae growth rates, reflect variation in both seasonal and interannual foraging (range: 2-8 years represented per vibrissae). Weaning signatures were present in a subset of the vibrissae, providing a unique opportunity to characterize the transition from dependence to independence. [THg] were positively associated with δ15 N, and several individuals had prolonged periods with concentrations above the toxicological threshold of concern. These findings provide a baseline for assessing shifts in foraging patterns relative to broad-scale environmental fluctuations, and can be compared to complementary data from female Steller sea lions to explore potential for intraspecific resource partitioning within Steller sea lion populations.
Alaska Marine Science Symposium 2023 260
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