Very low biodiversity of top predators—seabirds and marine mammals—in the high Arctic Ocean

Abstract

During the ARK-XXIII/3 expedition of icebreaking RV Polarstern in the high Arctic Ocean (partim north of 73°N) from 25 August to 10 October 2008, 550 transect counts lasting 30 min were devoted to seabird and marine mammal counts from the bridge. In the whole area, the three most numerous species, kittiwake Rissa tridactyla, fulmar Fulmarus glacialis and Brunnich’s guillemot Uria lomvia represented 90% of the total of 12000 individuals registered, followed by ivory gull Pagophila eburnea, black guillemot Cepphus grylle and Ross’s gull Rodostethia rosea. Four geographical zones were recognized on the basis of number of species and density. Both were especially low in the deeper areas (mean depth of 3000 m), both ice-free and heavily ice-covered: 0.3 birds per 30 min count belonging to three and four species respectively. The most numerous species was kittiwake with 0.25 per count (50 individuals) in the ice-covered area. Pinniped numbers were very low as well, the most numerous of the four species tallied being 20 harp seals Phoca groenlandica and 10 ringed seal Pusa hispida. Seven polar bears Ursus maritimus were encountered. These observations were basically confirmed during 12 helicopter flights lasting one hour each with very low numbers: 50 kittiwakes and 13 harp seals, almost none in the ice-covered deep zone. A comparison between data obtained from ship and from helicopter seems however to reflect the importance of seabird followers including for long distances. The only cetaceans were two adult belugas Delphinapterus leucas tallied from helicopter.