Trophic ecologies and dietary niches of Arctic charr (Salvelinus alpinus) and three coastal forage fishes in Frobisher Bay, Nunavut

Abstract

Here, the trophic ecology of four mid-trophic level fishes is described for an Arctic coastal marine habitat near Iqaluit, Nunavut. Arctic charr ( Salvelinus alpinus ), Arctic cod ( Boreogadus saida ), Fish Doctor ( Gymnelus viridis ), and sculpins (Cottidae) diet and feeding strategies were estimated using gut content; dietary niches were compared using stable isotopes (δ 13 C, δ 15 N); and relationships between diet indices and metrics of fish condition, including calorie content, were assessed. While the four taxa differed in foraging strategy, targeted prey, and the strength of associations with benthic and pelagic food web pathways, niche overlap occurred among the benthic and pelagic taxa. Pelagic Arctic charr and Arctic cod specialized in hyperbenthic amphipods and copepods, respectively, with evidence that selectivity was flexible. Fish Doctor and sculpins were benthic generalists with evidence for inter-individual and population-level specialization. Arctic charr occupied a central isotopic niche, resulting in a high probability of dietary niche overlap with the other three taxa. Fish Doctor and sculpins were likely to overlap with each other, and both had a low probability of overlap with Arctic cod. Isotopic diet indicators did not significantly explain variation in fish condition or calorie content. Findings reiterate the complex trophic ecologies that allow Arctic fish to divide resources and respond to changes in prey availability.

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