ARCTIC Density Distribution of Fish in the Presence of Whales at the Admiralty Inlet Landfast Ice Edge

ABSTRACT. Hydroacoustic techniques were used to search for fish beneath landfast sea ice in Admiralty Inlet, Northwest Territories, Canada, when narwhal (Monodon monoceros) and beluga whales (Delphinapterus leucar) were congregating at the ice edge in the mouth of the inlet. Fish, presumably Arctic cod (Boreogudussuidu), were distributed in the water column within four general layers or zones: near the ice undersurface, about 40 m deep, about 80-100 m deep, and about 150-200 m deep. The distribution of the first three layers roughly corresponded with the distribution of larger zooplankters, also estimated hydroacoustically. We recorded higher densities immediately below the ice than farther down in the water column. Maximum density in both regions occurred about 10 km from the ice edge. Fish density was low in the immediate vicinity of the ice edge. The distribution of fish underneath the landfast ice of Admiralty Inlet is postulated to have been influenced by the distribution of zooplankton, their principle food source, rather than by the presence of whales. Key words: Arctic cod, Boreogudus suidu, landfast ice edge, hydroacoustics, narwhal, beluga RÉSUMÉ. Des techniques hydroacoustiques ont t t t utilistes pour rechercher la prtsence de poissons sous la banquise côtitre de la baie de 1’AmirautC (Admiralty Inlet) dans les ‘Xrritoires du Nord-Ouest (Canada), au moment où des narvals (Monodon monoceros) et des Mgluas (Delphinapterus kucus) se rassemblaient A la lisikre des glaces A l’entrte de la baie. Des poissons, vraisemblablement des morues arctiques (Boreogudus suïdu), ttaient distributs dans la colonne d’eau en quatre grandes couches ou zones: prts du plafond glaciel et A des profondeurs respective d’environ 40,80-100 et 150-200 m. La distribution des trois premitres couches correspond grossierement A la distribution des organisme