Distribution and population size of the southern sea lion (Otaria flavescens) in central and southern Chubut, Patagonia, Argentina

Population size and distribution of Otaria flavescens in central and southe rn Chubut, Patagonia were determined by aerial censuses conducted during th e breeding season in 1989 and 1995 and outside the season. Pup numbers were corrected by means of a linear regression between pup and adult male (AM) numbers obtained from terrestrial censuses carried out in 1994 and 1996. Du ring the 1989 breeding season, 10,557 sea lions occurred at 29 locations; 2 ,800 (26.3%) were pups. During the 1995 breeding season, 14,887 animals wer e censused at 32 sites; 3,311 (22.2%) were pups. The corrected pup number i ncreased to 4,852, indicating that around 32% is lost when counting from ph otographs. The corrected total number increased to 16,483; this fell to les s than one half between breeding seasons (November 1990 and 1995). The 1995 breeding season census represents the highest number since 1972 (8,800) an d the widest historical dispersion (37 sites year round contrasting with 13 in the late 1940s and 1972). However, the present number is about one half of the 33,000 censused about 50 yr ago. Using a correction factor develope d for the north Patagonian population (1.8 X censused number) the present p opulation size in the area can be estimated at around 29,669 individuals.