Diets of four eelpout species (genus Lycodes) in the U.S. Beaufort Sea based on analyses of stomach contents and stable isotopes of nitrogen and carbon

Abstract

Eelpouts of the genus Lycodes are an abundant group of demersal fishes in the U.S. Beaufort Sea. Currently eelpout diet and the exact role of eelpouts in the Arctic food web are poorly understood. Additionally, if and how eelpouts avoid intra- and interspecific competition for resources is unknown. In this study, diets of four common Beaufort Sea eelpout species were analyzed with respect to along-shelf (longitude) gradients, across-shelf (depth) gradients, and ontogeny (fish body length) to determine diet composition and patterns of resource partitioning. Diets of the four most numerous eelpout species were analyzed using a combination of stomach contents and nitrogen and carbon stable isotope analyses: Adolf's Eelpout Lycodes adolfi, Canadian Eelpout L. polaris, Archers Eelpout L. sagittarius, and Longear Eelpout L. seminudus. Nitrogen stable isotopes of fish tissue were analyzed to determine trophic level and carbon stable isotopes to determine if origin sources of carbon in food web pathways of eelpout diets differed among species. Fishes were collected in the central (2012) and eastern (2013 and 2014) Beaufort Sea in August and September as part of the U.S.-Canada Transboundary program. Prey groups Polychaeta, Amphipoda, Isopoda, Ophiuroidea, and Copepoda composed a large proportion of the diet by percent weight for all four species of Lycodes, but their relative contributions differed among the species examined. This study indicated that eelpouts feed almost exclusively on benthic prey and avoid interspecific competition by occupying different habitat space and having different diets. Intraspecific similarity in diet composition was low suggesting these fish have diverse diets even among individuals of the same species. Fish length was associated with changes in diet composition for L. adolfi and L. sagittarius, but not L. polaris and L. seminudus. Longitude and depth were correlated with shifts in diet composition for L. sagittarius, but not the other three species. Lycodes polaris occupied a lower trophic level than the other three eelpout species based on nitrogen stable isotope values. Despite differences in the across-shelf distribution between L. polaris and the three deep-water eelpout species, carbon sources of diet were indistinguishable among the four eelpout species. Ecological information on abundant Arctic fish species like eelpouts is needed for long-term ecosystem monitoring, which is especially important in light of pronounced climate changes and increased human activities in the Arctic.