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    Compound-specific stable isotopes of amino acids reveal the influence of trophic level and primary production sources on mercury concentrations in fishes from the Aleutian Islands, Alaska

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    Chair
    Barst, Benjamin
    Wooller, Matthew
    Committee
    Horstmann, Lara
    Keyword
    Fishes
    Mercury
    Aleutian Islands
    Steller's sea lion
    Methylmercury
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/13132
    Abstract
    Total mercury (THg) concentrations exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus; SSL) tissues from certain portions of the Aleutian Islands, Alaska. Here, compound-specific stable isotope analyses (CSIA) of carbon in essential amino acids ([delta]¹³CEAA values) and nitrogen in AAs ([delta]¹⁵NAA values) in fish muscle tissue was applied to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of SSL diets. Previous THg analyses of fish muscle, coupled with additional monomethylmercury (MMHg) analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle THg concentrations relative to fishes from east of the pass. All fish muscle samples were analyzed separately for, both, CSIA-AA of carbon and nitrogen. The [delta]¹³CEAA values in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this primary production source. Certain [delta]¹⁵NAA values of the same fish samples indicated that trophic positions of fishes were higher from the west relative to the east of the pass for some species. Total Hg was positively correlated with bulk [delta]¹⁵N values, [delta]¹⁵N values of glutamic acid ([delta]¹⁵NGlu), and trophic positions. However, only trophic magnification slopes using [delta]¹⁵NGlu values indicated a higher rate of Hg biomagnification to the west of Amchitka Pass. Broad and species-level multiple linear regression models revealed that trophic position was the most important driver of fish muscle THg with a smaller amount of variation explained by other parameters, such as proportional contributions of primary production sources, fish body condition, and catch location. Collectively, results indicate that differences in fish trophic positions were the most consistent determinants of the higher fish THg concentrations to the west of Amchitka Pass. However, a higher rate of THg biomagnification to the west of Amchitka Pass may also play a role in the regional differences in fish muscle THg.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2022
    Table of Contents
    Introduction -- Methods -- Study site and sample collection -- Mercury analyses -- Compound-specific stable isotope analyses of amino acids -- Data handling and statistical analyses -- Results -- Total mercury and methylmercury -- Compound-specific stable isotope analyses of carbon in amino acids -- Compound-specific stable isotope analyses of nitrogen in amino acids -- Multiple linear regression models -- Discussion -- Overview -- Fingerprinting and proportional contributions of primary producer essential amino acids to fishes -- Trophic position and mercury biomagnification -- Rates of mercury biomagnification -- Multiple linear regression modeling -- Implications for Steller sea lions of the western Distinct Population Segment -- Conclusion -- References -- Tables -- Figures -- Appendix.
    Date
    2022-12
    Type
    Thesis
    Collections
    Marine Sciences

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