Abstract

Otariids exhibit a semiaquatic lifestyle, feeding in the water and breeding and resting on land. Fur seals and sea lions, the two groups of otariids, exhibit an overall income breeding system where the females alternate between trips to the foraging grounds and periods at the breeding colony to feed the pup. How far and how long lactating females can be away from their foraging trips is ultimately dictated by ecological and physiological tradeoffs. In this chapter, we examine the interrelations between behavior and physiology and how they enable or constrain the reproductive, foraging biology, and life history of otariids. For example, income breeding limits otariid females to forage near their reproductive colonies, which constrains them to inhabit highly productive oceanographic regions. Further, as sea lions are larger than fur seals they are capable of deeper and longer dives. As a result, fur seals tend to feed closer to the surface in the epipelagic regions, while sea lions tend to forage in deeper environments on benthic, epipelagic and mesopelagic prey. We review the patterns of resource acquisition and allocation, including an examination of the energetics of reproduction, milk composition, foraging behavior, and differences between fur seals and sea lions. Further, we assess how these factors may have led to their current distribution and demographic trends during the last decades. We finish by discussing how these physiological and ecological tradeoffs would have influenced the evolutionary history of otariids in the deep time.