ABUNDANCE AND DISTRIBUTION OF PHOCID SEALS ON ICE IN THE WESTERN BERING SEA IN SPRING, 2012–2013

Abstract

Abundance and density distribution of four seal species (ringed, ribbon, spotted, and bearded) on spring ice was estimated based on the data from two instrumental aerial surveys in the western Bering Sea in April-May 2012 and April 2013 and compared with the previously published values. The number of ringed seals on ice was about 61,000, they were rather evenly distributed in the southern, middle and northern parts of the Russian EEZ in the Bering Sea. The estimated number of ribbon seals was about 62,000 in 2012, but only 15,000 in 2013. The number of bearded seals was estimated as 42,000 animals. The abundance and density distribution of spotted seals was shown to be a subject of significant interannual fluctuations with the maximum of about 97,000 individuals. The spotted or ribbon seals were not found in the Anadyr Bay, but importance of the Karaginsky Bay for reproduction of the phocid seals was confirmed. A large population of spotted seals was concentrated there and the ringed and bearded seals were presented there in the highest recorded density. Effectiveness of the instrumental aerial survey method application for assessing abundance and distribution of seals on sea ice was demonstrated. However, in order to estimate the real population abundance, it is essential to apply correction coefficients allowing to account for behavioural and migration processes predefining the proportion of seals available for detection.

Keywords

• instrumental aerial survey
• phocid seals
• seal abundance
• seal distribution
• ringed seal
• ribbon seal
• spotted seal
• bearded seal
• bering sea