Prolonged fasting in pinnipeds

Abstract

Marine mammals are capable of fasting for extremely long periods at different stages of their life cycle. The first objective of this thesis was to determine how plasma chemistry changed during fasting in large free-ranging phocids, northern elephant seal pups. Next, elephant seals of very low (LWM) and very high weaning mass (HWM) were examined to address how weaning mass impacts fasting chemistry. In the third section, blood chemistry was utilized to study the transition from suckling to weaning in Weddell seal pups, because behavioral verification of weaning is difficult in this species. Lastly, blood chemistry and body morphology of Steller sea lion pups were examined for indications of possible nutritional deficiency that could be associated with apparent declines in juvenile survival of sea lions in Alaska. In average mass (AWM) elephant seals, changes in blood urea nitrogen (BUN), non-esterified fatty acid (NEFA) and beta-hydroxybutyrate ($\beta$-HBA) concentrations provide strong evidence that the pups effectively minimize protein loss through increased reliance on lipid metabolism and ketone body production early in the fast. Elephant seals maintain this phase of protein sparing for up to 11 weeks. Size of elephant seal pups at weaning influenced how stored fuels were utilized during the fast. LWM pups showed higher NEFA and $\beta$-HBA levels than average or HWM pups but showed no indication of increasing protein mobilization before they left the beach. HWM pups showed evidence that they may be able spare more protein than average pups. Plasma metabolite levels and the accompanying rates of mass change suggest that Weddell seal pups typically fast after weaning. High $\beta$-HBA concentrations seen within 1 to 3 weeks of weaning are similar to levels seen during the first 3 weeks of fasting in other phocid species. Blood chemistry and body morphology data collected from 168 Steller sea lion pups showed no indication that young pups from areas of population decline were nutritionally compromised. The clinical plasma chemistry profiles showed no indication of general poor health in any of the areas studied.