Date of Award

5-17-2024

Document Type

Thesis

Abstract

Body tissue chemistry has been extensively utilized as biomarkers about the cryptic life histories of Steller sea lions (Eumetopias jubatus) in the western and central Aleutian Islands, Alaska, specifically tissue total mercury concentrations and stable isotope ratios of carbon and nitrogen. As patterns in these biomarkers can be associated with either trophic dynamics or environmental conditions, I examined spatiotemporal and biological variability of bulk carbon and nitrogen stable isotope ratios and total mercury concentrations in the muscle tissue of ten fishes and two cephalopods found in Steller sea lion diets. I hypothesized that the complex bathymetry and oceanography of the region associated with deep-water "oceanic passes" separating islands may limit movement of these species between island groups, compartmentalizing communities in a manner to create distinct geochemical groups. In my first chapter, I found that several oceanic passes act as break points in an east to west decrease in carbon and nitrogen stable isotope ratios in most species sampled, suggesting island groups of the Aleutian Islands have distinct environmental baseline chemistry and/or primary production dynamics. In my second chapter, I found that total mercury concentrations in muscle tissues decrease with distance from the Rat Island group. When this spatial variation was accounted for and species were grouped by feeding guild, benthic invertebrate consumers had the highest mercury concentrations, followed by piscivores and then zooplankton consumers. Multiple species-specific relationships between length and each of these trophic biomarkers provided additional insight into trophic dynamics of these prey species in addition to spatial variation. Considered together, trophic biomarker patterns in Steller sea lion prey suggest trophic networks in the Aleutian Islands are spatially compartmentalized, and variation in sea lion tissue biochemistry will depend on where and what they forage upon in remarkably nuanced manners.

Handle

http://hdl.handle.net/11122/15133

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