UC Santa Cruz

The integration of physiological and behavioral studies can yield valuable information important to the conservation and management of imperiled species. In the following chapters, I examine a suite of physiological characteristics and behavioral attributes of southern sea otters (Enhydra lutris nereis) across a variety of life stages and discuss resulting population level consequences in this threatened species. In my first data chapter (Chapter 2), I use open-flow respirometry to determine age- and activity- specific metabolic rates of immature southern sea otters throughout ontogeny. These data are then combined with activity budgets of wild sea otters to determine the energetic cost of pup rearing for adult females. In Chapter 3, I determine age-specific oxygen storage capacity and diving abilities of sea otters from birth through adulthood. Finally, in Chapter 4, I examine the foraging behavior of sea otters off the coast of central California. I found that sea otter pups have elevated mass-specific metabolic rates in comparison to adult conspecifics, which are highest for molting pups and begin to approach adult levels around the average age of weaning (6 mo.). In addition, immature sea otters have limited blood and muscle oxygen stores throughout dependency, which result in a limited capacity for diving and high dependence on adult females throughout lactation. The high energetic demands of pups result in elevated field metabolic rates (FMR) for lactating females. Female FMR is increased 17% by three weeks postpartum and continues to increase throughout lactation. By the average age of weaning female FMR is increased 96% above pre-pregnancy levels. These heightened energetic demands are reflected in the foraging behavior of wild sea otters. Adult females appear behaviorally constrained by dependent young during an already energetically costly life stage. Both physiological and behavioral data suggest that it takes sea otters approximately two years to develop comparable diving abilities to adults; however, individuals at this stage are likely inefficient foragers when compared to adults. Together these data indicate that late-lactation and the first years post-weaning are the most physiologically challenging life stages for sea otters and that these groups are likely the most sensitive to disturbance and resource limitation. The high energetic demands of dependent pups influence body condition, parental provisioning strategies, and life history decisions in adult females. In addition, high energy demands, physiological limitations, and behavioral naïveté make maintaining positive energy balance difficult for juvenile and sub-adult sea otters. Ultimately, these chapters provide novel information regarding age-specific energy demands, physiological abilities, and foraging behavior of southern sea otters across a variety of life stages, and elucidate mechanisms underlying current population level trends.