Bering Sea | Mammals
Using longitudinal profiles of δ13C and δ15N in Steller sea lion pup vibrissae to assess relationships among sex, mass, mercury concentrations, and relative age at Agattu Island Presenter: Stephanie Crawford , sgcrawford@alaska.edu, University of Alaska Fairbanks Lorrie Rea , ldrea@alaska.edu, University of Alaska - Fairbanks Elevated total mercury concentrations ([THg]) in the hair of some young Steller sea lion (SSL) pups are well-documented. In other mammalian piscivores, fetuses exposed to high mercury concentrations have lower birth weights and reduced survival. While SSLs exhibit a synchronous parturition period, pups could be within several weeks age of one another during a late June/early July field capture. Some variability in mass of these pups could be attributable to relatively small differences in age as pups grow over these first few weeks. Aging pups during field captures based upon physical characteristics and morphometrics is imprecise. Therefore, we used stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) from serially-sampled vibrissae (begin growing during mid-gestation) to identify the inflection point at which milk consumption is detected (depleted δ13C). The distance from the root (most recent growth) to this inflection point serves as an index to relative pup age. Pups were sampled at the western Aleutian Island of Agattu (n=219) during each odd year 2011–2019. Agattu Island was chosen for this initial review with relative age as there are a broad range of [THg] observed, and Agattu remains a location with a decreasing population trend. Using hair [THg], pups were categorized as low- (<10 ug/g), moderate- (≥10 and <20 ug/g), and high- (≥20 ug/g) risk of adverse toxicological effects from Hg. Not surprisingly, pups born earliest had the greatest mass at time of handling (p<0.05), and there was evidence of a slight shift towards more males being born earlier in the parturition period than female pups. Pups born earlier in the season tended to have lower [THg], but this was not statistically significant (p=0.0724). Understanding these patterns and how they change over time and in relation to environmental variability could help to explain recent population trends.
Alaska Marine Science Symposium 2023 264
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