Aerial survey of Baltic ringed seals (Pusa hispida botnica) in the Russian part of the Gulf of Finland
An aerial survey with the use of method of strip transects was carried out on April, 20th, 2010 in the Gulf of Finland, when the great majority of ringed seals were hauled out on ice during the moulting period. The total ice-covered area was 2062 km2, but only 58 % (1194 km2) was covered by strip transects due to the military restrictions. The observed number of ringed seals in strips was 6 only. The average density of ringed seal in strips was 0,022 seals/km2 (SE = 0,008). The sampling fraction was 23,3 % from 1194 km2 of the ice, and the resulting estimate was 26 (SE = 9,13) hauled-out ringed seals. Total abundance estimate was an extrapolation over total ice-covered area. The estimate for the whole ice-covered area in the Russian part of the Gulf of Finland would be 45 (SE = 16,74) seals with rather wide 95 % confidence limits from 12 up to 77. The research reveals a strong tendency that the number of ringed seal is considerably lower than reported ten years ago. The Baltic ringed seal is on the edge of extinction within the Russian part of the range.
Baltic ringed seal, the Gulf of Finland, aerial survey, abundance estimation, population decline
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