Abstract:

The population status of southern sea lions (Otaria flavescens) in southern Argentina (provinces of Santa Cruz and Tierra del Fuego) was last assessed between 1946 and 1949, when there were 49 colonies with 84,714 individuals and a production of 12,658 pups recorded. To update the population size and pup production a new series of surveys was carried out during 1992 and 1997, either from land, airplane or boat, using direct counts in the field or pictures. The number of pups was corrected using data from land-based counts. Overall, we recorded 53 colonies, with a minimum number of 12,310 animals present on land, including 2925 pups. This estimate represents a decrease to only 14.5% of the population size reported in the late 1940's. Applying a correction factor for animals in the water, the estimated total population was 22,157 individuals. The sealing activities performed mainly at northern Patagonia and at Tierra del Fuego are likely to be responsible for the depletion. We also detected changes in the location of the colonies. However, seasonal movements of animals were difficult to assess due to the scarce data available. Only four breeding colonies may be considered permanent. Seasonal movements would take place between the islets close to Ushuaia city and Islas Becasses. Southern Argentina does not hold large breeding colonies like those found, for example, in northern Patagonia. Juveniles predominate in the social structure of colonies. This suggests a likely increase in the coming years.