WEISE, Michael / J; COSTA, Daniel / P; Univ. of CA Santa Cruz: Diving Behavior of the Male California Sea Lion (Zalophus californianus)

Intraspecific differences in foraging and diving behavior of males and females have been found in a variety of marine predator species. Among the hypotheses to describe sex differences in foraging behavior are sexual size dimorphism, reduced intersexual competition for food, and differential roles of each sex during breeding. For example, among true seals (Family Phocidae), the sexually dimorphic species, the northern elephant seal (Mirounga angustirostris) has distinct differences in diving behavior between the sexes. While all fur seals and sea lions (Family Otariidae) are sexually dimorphic, few studies have examined the diving behavior of male otariids and fewer studies have compared intersexual differences. Male California sea lions are up to four times larger in mass than females, and are thought to migrate northward along the West Coast following the summer breeding season in the Channel Islands and return southward in the spring. Here we examine the diving behavior of male California sea lions with a view to elucidating the effects of size dimorphism, intersexual competition for food resources, and different roles in reproduction. Using satellite linked depth recorders we examined the spatial and temporal diving behavior of 22 male sea lions for up to 3 months during their northward migration. Based on their larger body size, male sea lions will have greater absolute metabolic requirements but increased diving capability. Therefore, we predict that male sea lions will employ different diving strategies than females and exploit the same or deeper regions within the water column than females. We predict little intersexual competition for food resources due to differences in the spatial distribution of foraging effort between males and females.