Changes in social composition and spatial distribution of colonies in an expanding population of South American sea lions, Otaria flavescens

FLORENCIA GRANDI,; SILVANA DANS; ENRIQUE CRESPO

JOURNAL OF MAMMALOGY

Allen Press

Año: 2008 vol. 89 p. 1218 - 1228

0022-2372

In northern Patagonia, South American sea lions are increasing in number after a depletive harvest. There has been an expansion of colonies with an increase of pup numbers, changes in social composition and spatial distribution. Using annual counts of four different age classes from 1972-2007 we found that new colonies change their social composition, transforming from haul-out sites to breeding while passing through mixed structures. From this pattern we can hypothesize that at dense breeding sites the shortage of space or the avoidance of intraspecific harassment promotes dispersal by first-time breeders to suitable sites nearby. Such mechanisms along with philopatry and site fidelity will promote the establishment of new breeding colonies nearer to existing breeding colonies than would be expected by chance. There was significant spatial clustering of new breeding colonies around the 7 focal (established) colonies. This spatial pattern was consistent through time. New breeding colonies were closer to focal colonies than non-breeding ones, suggesting a ‘spill-over’ effect, where young individuals would choose to breed near to established breeders. The colonization mechanism we found suggests that potential areas for population expansion could be closer to areas where growing colonies already exist and highlights the importance of  the juvenile age classes and the areas adjacent to colonies in the overall recovery of any population of pinnipeds.