Limited effects of changing prey fish communities on food quality for aquatic predators in the eastern Canadian Arctic in terms of essential fatty acids, methylmercury and selenium

Abstract

We determined concentrations of eicosapentaenoic and docosahexaenoic acids (EPA + DHA), Σomega-3, polyunsaturated fatty acids (ΣPUFA), selenium, methylmercury, and selenium:methylmercury (Se:Hg) ratios in native and northward-redistributing sub-Arctic marine fish and invertebrates from low, mid-, and high Canadian Arctic latitudes. There was no clear latitudinal trend in nutrient or contaminant concentrations. Among species, EPA + DHA concentrations in native Arctic cod (Boreogadus saida) were similar to concentrations in sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) (444–658 mg.100 g-1), and higher than in most other species. Concentrations of EPA + DHA were related to lipid content, but to a greater extent for higher trophic position species (R2 = 0.83) than for species at lower trophic positions (R2 = 0.61). Selenium concentrations were higher in sand lance (1.15 ± 0.16 μg g−1) than in all other species (0.30–0.69 μg g−1), which was significantly, but weakly, explained by more pelagic feeding in sand lance. Methylmercury concentrations were similar (and Se:Hg ratios were higher) in capelin, sand lance, and Arctic cod (0.01–0.03 μg g−1 wet weight (ww)) and lower than in other prey (0.12–0.26 μg g−1 ww), which was significantly explained by the smaller size of these species and more pelagic feeding habits than other fish. These results suggested that a shift in prey fish composition from Arctic cod to capelin and/or sand lance is unlikely to reduce the food quality of the prey available to marine predators at least with respect to concentrations of essential fatty acids, selenium, and Se:Hg ratios.