Trophic variability of Arctic fishes in the Canadian Beaufort Sea: a fatty acids and stable isotopes approach

Trophic ecology of most demersal Arctic fishes remains one of the major knowledge gaps for understanding food web dynamics and connectivity among ecosystems. In this study, fatty acids (FA) and stable isotopes (SI) were used to study the feeding ecology of seven species (n = 106) of the most abundant benthic fishes (eelpouts, sculpins and agonids) in the Canadian Beaufort Sea from shallow (20–75 m), slope (200–350 m) and deep (500–1000 m) habitats. Both FA and SI results revealed among- and within-species variability in diet composition. Correspondence analysis of FA signatures identified high within-species variability in diet, resulting in high overlap among species. Calanus-derived FA were present in all species (Calanus markers up to 13 % of total FA) and were particularly important in Ribbed Sculpin, Adolf’s and Longear Eelpout collected in deep habitats, suggesting a strong contribution of pelagic-derived FA to benthic fish communities. Incorporation of this signal in the benthos may result from either direct consumption of deep overwintering copepods (i.e., off-bottom feeding) or through detrital accumulation in benthic invertebrate prey. Mean SI values differed among species and indicated that a large range of trophic positions (δ¹⁵N varied from 14.09 to 17.71 ‰ for Canadian Eelpout and Adolf’s Eelpout, respectively) and carbon dietary sources are preyed upon (δ¹³C range from ?21.13 to ?23.85 ‰ for Longear Eelpout and Ribbed Sculpin, respectively). SI analyses suggested that most species examined were low- to mid-trophic generalist benthic carnivores, with the exception of Ribbed Sculpin, which was a low-trophic pelagic predator.