ARCTIC Occurrence of Arctic Cod (Boreogadus saida) Schools and Their Vulnerability to Predation in the Canadian High Arctic

ABSTRACT. We document the occurrence of large schools of Arctic cod (Boreogadus saida) in the Barrow Strait region of the eastern Canadian Arctic during the open water season. Schools were most frequently observed near shore, often in depressions inside bays. Schools ranged up to 130 O00 mz surface area and contained on the order of 4 X 108 fish, weighing 12 O00 tonnes. Evidence indicates that schools form before the arrival of predators, but when they occur in shallow water, they are often subjected to intense predation by thousands of seabirds and marine mammals, primarily black-legged kittiwakes (Rissa tridacfyla), northern fulmars (Fulmam glacialis), harp seals (Phoca groenlandicus), beluga (Delphinaptem Zeucas) and narwhal (Monodon monoceros). The reasons for such schooling behavior are unknown. Key words: arctic Canada, Arctic cod, schooling, marine mammals, seabirds, predation, beluga, harp seals, ringed seals &SUMÉ. On 6tudie la presence de grands bancs de morue arctique (Boreogudus saida) dans la region du detroit de Barrow situ & dans l’Arctique canadien oriental durant la saison d’eau libre. On a observe que les bancs se tenaient le plus frkquemment pr&s du rivage, souvent dans des dépressions B l’interieur des baies. Les bancs couvraient jusqu’h 130 O00 mz et comptaient en gros 4 X lo8 poissons, pour un poids total de 12 O00 tonnes. L’&de rkvkle que les bancs se constituent avant I’arrivke des prtklateurs, mais lorsqu’ils se trouvent dans des eaux peu profondes, ils sont souvent la proie de milliers d’oiseaux et mammiRres marins voraces, en particulier la mouette tridactyle (Rissa tridactylu), le fulmar boreal (Fulmam glacialis), le phoque du Groenland (Phoca groenlandicus), le Mluga (Delphinapterus leucas), et le narval (Monodon rnonoceros). On ne connaît pas les causes du regroupement des poissons en bancs