Travel for sex: Long-range breeding dispersal and winter haulout fidelity in southern sea lion males

Southern sea lions (Otaria flavescens; SSLs) have a polygynous mating system and a prolonged social-sexual maturation period for males. Male haulouts are common in this species, with some very distant from central breeding rookeries, although the functions of these aggregations are not clearly understood. To estimate the potential connectivity between northern Argentina male colonies and breeding rookeries in Patagonia and Uruguay, we monitored the summer breeding activities and winter presence of 559 individually identified SSL males from haulouts in Mar del Plata and Quequén harbors. Our results confirm that male groups are formed by sexually active sea lions that show a strong annual connection with distant (up to 700 km) breeding colonies. Circa 70% of the marked males made long-distance round-trips (72 ± 26.7 days; n = 325) from northern Argentina to Patagonia and Uruguay, indicating a high degree of winter site fidelity. Mating activity was confirmed for 53% of the sea lions re-sighted in breeding colonies, with approximately 80% of them having central positions on the beach and holding harems of up to nine females. The chronology of this cycle is finely tuned with the onset of the breeding season, which may result in comparative advantages such as anticipating female arrival or a prolonged participation in mating activities. Our results suggest a model of male haulouts spatially segregated from the central breeding areas, but with a summer recurrent flow of animals that contributes a significant proportion of the male population of northern Patagonia and Uruguay.