Schooling behaviour of arctic cod, Boreogadus saida, in relation to drifting pack ice

Abstract

SynopsisConcentrations of arctic cod were detected with a hydroacoustic system in Resolute Bay, NWT during 2 weeks in August of 1986. Fish biomass within the bay was about 30 t. The fish were feeding primarily on amphipods, which were abundant. When the daily location of the schools was examined in relation to the extent and position of drifting pack ice, a pattern emerged suggesting that the distribution of the fish was influenced by the amount and location of ice cover. If the bay was relatively ice-free, the density of schooling cod was high and the size of the schools, as 2-dimensional surface area, was generally small. When ice covered the bay, density within the schools was lower and they occupied more area. Arctic cod were most dispersed after the bay had been filled with pack ice for several days. It is postulated that this behaviour is a response to potential predation by seabirds and marine mammals.

Hydrographic Features, Cetaceans and the Foraging of Thick-billed Murres snd Other Marine Birds in the Northwestern Barents Sea

“…The species is widely distributed in the northern Barents Sea during summer (Gjøsaeter and Anthonypillai, 1995) and is an important element in the arctic marine food chains (Bradstreet and Cross, 1982;Welch et al, 1992;Mehlum and Gabrielsen, 1993). In Canadian coastal waters, this species may aggregate in dense schools from 3 to 5 m below the surface during late summer (Crawford and Jorgenson, 1993;Welch et al, 1993).…”

Ringed Seals and Sea Ice in Canada’s Western Arctic: Harvest-Based Monitoring 1992–2011

“…Ringed seals are vulnerable to ecosystem shifts, and prime ringed seal breeding habitat must also be located near readily available food (Smith, 1987). The ringed seals' main prey is arctic cod, Boreogadus saida (Johnson et al, 1966;Lowry et al, 1978Lowry et al, , 1980Bradstreet et al, 1986;Crawford and Jorgenson, 1993;Crawford et al, 2011), and invertebrates also form a main part of their diet in certain areas and years, particularly for subadults. Adult female ringed seals forage for food while actively tending their pups (Smith and Hammill, 1981;Hammill et al, 1991;Smith et al, 1991;Kelly and Wartzok, 1996).…”

Observations and Predictions of Arctic Climatic Change: Potential Effects on Marine Mammals

“…Cryopelagic fishes such as arctic cod (B. saida) are especially adapted to feed under the ice where they rely on crustaceans associated with the ice undersurface and the adjacent water column (Lønne and Gulliksen, 1989), primarily amphipods (i.e., Onisimus spp., Apherusa glacialis, and Parathemisto libellula) and copepods (i.e., Calanus glacialis and C. finmarchicus) (Alexander, 1981;Dunbar, 1981;Bradstreet et al, 1986;Lønne and Gulliksen, 1989;Crawford and Jorgenson, 1993). Further, the placement and orientation of the mouth of arctic cod suggests an adaptation to under-ice feeding (Dunbar, 1981).…”

“…The arctic cod is a pivotal species in the arctic food web, as evidenced by its importance as a prey item to belugas, narwhals, harp seals, ringed seals, bearded seals, and hooded seals (Cystophora cristata) (Davis et al, 1980;Bradstreet, 1982;Bradstreet et al, 1986;Ainley and DeMaster, 1990;Borkin, 1990;Finley et al, 1990a;Welch et al, 1992;Crawford and Jorgenson, 1993). In arctic regions, no other prey items compare with arctic cod in abundance and energetic value (Finley et al, 1990a).…”

“…In arctic regions, no other prey items compare with arctic cod in abundance and energetic value (Finley et al, 1990a). The distribution and diet of arctic cod vary with ice conditions (Frost and Lowry, 1984;Crawford and Jorgenson, 1993) and large numbers of fish can occur locally, especially in areas of marginal ice zones (Andriashev, 1970). Therefore, the trophic cascade upon which arctic marine mammals depend is ultimately driven by the complex interactions between ice, light penetration, nutrient supply, and productivity.…”