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Abstract CONTRIBUTION OF COMMERCIAL FISHING TO THE DECLINE IN HAWAIIAN MONK SEALS Charles W. Potter1 and Amy C. Hirons2 Recorded declines of Hawaiian monk seals (Monachus schauinslandi) have occurred over the past half century in the Leeward Chain of the Hawaiian Islands. Preliminary evidence from stable carbon (13C/12C) and nitrogen (15N/14N) isotope ratios in bone collagen from the seals (n=30) shows a shift in both isotopes between the 1920s and 1960s, indicative of a diet switch, possibly from a benthic diet (crustaceans, mollusks) to a more pelagic diet (fish). We surmise the advent of commercial fishing of potential prey items post-World War II led to the decline of preferential prey items and forced the seals to utilize prey species potentially less nutritious and/or which require more energy to capture. Less nutritious prey could be at least partially responsible for the reproductive failure and overall decline of Monachus throughout its range. These historic isotopic values are compared to modern seals and potential prey from the main Hawaiian Islands with the current assumption that the isotope signatures are similar with the Leeward Islands of the chain. This on-going study will examine stable isotope values from seals and potential prey items from the Leeward Islands to establish modern trophic linkages for more direct comparisons in reconstructing their historic food webs.
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