Resource partitioning may limit interspecific competition among Arctic fish species during early life

Arctic cod (Boreogadus saida) strongly dominates the ichthyoplankton assemblages of High Arctic seas, hence competition with other native species seldom has been studied. Yet, interspecific competition could negatively impact the survival of early life stages of fishes in Arctic areas where higher diversity prevails. We surveyed the ichthyoplankton community of the Greenland Sea, in August-September 2017. Gadids (mostly Arctic cod, with a low number of ice cod Arctogadus glacialis) and non-gadids (bigeye sculpin Triglops nybelini and gelatinous snailfish Liparis fabricii) co-dominated age-0 fish assemblages. Here, we document their diet, prey selectivity, horizontal and vertical distributions as well as that of their prey to assess resource partitioning and the potential for interspecific competition. All fish species occupied the top 30 m of the water column, but Arctic cod occurred in highest abundances over the continental slope, whereas other species distributed almost exclusively over the continental shelf. A particle track analysis suggests that Arctic cod larvae could have hatched in the open waters of the Northeast Water Polynya, drifted with the East Greenland Current, and benefited from the high secondary production associated with these oceanographic features. The diet of gadids did not overlap significantly with the diet of non-gadids, but strong selectivity for Pseudocalanus spp. and Calanus spp. copepodites among the larvae suggests potential competition for these key prey items, although limited by size partitioning of the prey. We thus conclude that interspecific competition among early life stages of Arctic fishes is limited for now. However, changing conditions and the northward range expansion of boreal species following climate change could increase competition and, in turn, negatively affect the recruitment of Arctic ichthyoplankton.