Summer foraging behaviour of shallow-diving seabirds and distribution of their prey, Arctic cod ( Boreogadus saida ), in the Canadian Arctic

Abstract

Productive areas in the Canadian Arctic seasonally provide top predators with accessible and often predictable sources of energy. Arctic cod (Boreogadus saida) aggregate in shallow bays during the summer and are exploited by seabirds and marine mammals. Information concerning how prey is presented to predatory seabirds, and the cues seabirds use to optimize foraging potential, is limited. Hydroacoustic surveys were completed in Allen Bay, Nunavut, to determine the presence, density, abundance, and depth of Arctic cod schools in relation to shallow-diving seabirds. Schools were also documented using standardized protocols to examine the influence of environmental variables, such as wind, ice, tidal states and seabird behaviour. The presence of schools was a significant predictor of the distribution of northern fulmars (Fulmarus glacialis) but not black-legged kittiwakes (Rissa tridactyla). Glaucous gulls (Larus hyperboreus) associated with northern fulmars are likely optimizing chances of stealing Arctic cod. The density, size and depth of schools did not significantly affect the distribution of the seabirds. We speculate that Arctic cod from demersal schools separate to feed at the surface in satellite schools (groups of dispersed fish), thus reducing competition but increasing the risk of predation.