Aerial census of ringed seals Pusa hispida basking on the ice of the Bothnian Bay, Baltic

• Published in: Ecography
• Main Author: Helle, Eero
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1980
• Subjects: Pusa hispida; ringed seal
• Online Access: http://dx.doi.org/10.1111/j.1600-0587.1980.tb00724.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1600-0587.1980.tb00724.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0587.1980.tb00724.x

The censuses are based on six surveys (1590 km total) carried out between 13 April and 17 May 1975 and two surveys (560 km) on 13 and 15 May 1978. The material consists of 716 observations in 1975 and 214 observations in 1978, involving 1960 and 572 ringed seal specimens respectively. The transect width was determined in retrospect on the basis of the sighting angle and sighting distance, the latter being estimated and corrected by a factor typical for each separate flight. The mean sighting distances varied from 720 to 1140 m with a range from 160 to 2450 m. On average over 3000 ringed seats were basking on the ice of the Bothnian Bay in 1975 and 1978, promising at least 4000 specimens living in the area in total. Sources of methodological bias, factors affecting the observability of the seals, and the estimation of the total population based on the numbers of basking seals are discussed.