Lipid removal and acidification affect nitrogen and carbon stable isotope ratios of beluga whales (Delphinapterus leucas) and their potential prey species in the Beaufort Sea ecosystem
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Carbon and nitrogen stable isotope ratios are ecological tracers that can provide insights into the diets of marine mammals. As a generalist predator, beluga whales (Delphinapterus leucas) consume a variety of prey; however, differences in lipid content and the presence of inorganic carbon in prey may cause variability in the δ13C signal that is not related to food sources. We examined the effects of carbonate and/or lipid removal in beluga and potential prey and tested whether the C:N ratio was a valid indicator of lipid content. The C:N ratio was a good predictor of the change in δ13C after lipid removal in capelin (Mallotus villosus), octopus (Cirroteuthis muelleri), green shrimp (Argis dentata), and circumpolar eualid (Eualus gaimardii). Despite relatively low C:N ratios, lipid removal significantly increased δ13C values, but also affected δ15N. Removal of carbonates from invertebrate samples significantly decreased δ13C values and had variable effects on δ15N. Overall, the variability in δ13C within a species decreased after removing lipids and carbonates. Variability in δ15N did not change for species requiring only lipid removal, but increased after acidification. We also evaluated the effect of these sample preparation methods on niche dispersion metrics. After lipid and carbonate treatments, centroid locations differed significantly in all species except beluga muscle, and niche breadth and mean distance to the centroid decreased. Failure to remove lipids and carbonates for δ13C values may lead to incorrect interpretations for isotopic niche, which may have major ecological implications, such as predicting the impacts of invasive species or determining the dietary linkages of beluga whales.
KeywordsLipid Content Niche Breadth Stable Isotope Ratio Carbonate Removal Isotopic Niche
This project was supported by a Natural Science and Engineering Research Council (NSERC) Doctoral Scholarship, UNESCO-L’Oreal Women in Science PhD Fellowship, E. Scherer Memorial Scholarship, Lorraine Allison Memorial Scholarship, Arctic Institute of North America (AINA) Grant-in-Aid Program, and the Association of Canadian University for Northern Studies (ACUNS) W. Garfield Weston Northern Research Award to EC. Project funding was provided by Fisheries and Oceans Canada, Fisheries Joint Management Committee, Northern Science Training Program and the Northern Contaminants Program. We would like to thank Shannon MacPhee for coordinating the BREA benthic program and Laure de Montety for identifying the invertebrate samples. We would also like to thank Sheila Atchison and Andy Majewski for collecting the capelin samples, as well as beluga monitors Frank Pokiak, John Day, and Brandon Green for collecting muscle and liver tissues. Maps of the beluga hunting camps and BREA transects were provided by Mark Ouellette. We are grateful for the support and partnerships of the Hunters and Trappers Committees of Inuvik, Tuktoyaktuk, and Paulatuk. We would like to thank our reviewers for their valuable feedback.
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