Investigations of the role of lipids in marine mammal diets, health and ecology

Abstract

Lipids are essential to many aspects of marine mammal biology. I investigated the amount, type and flux of lipids under a variety of natural and controlled nutritional and dietary conditions, in order to increase our knowledge of marine mammal diets, health and ecology. First, I examined the influence of biological and environmental variables on the quantity and quality of blubber, and their importance in establishing condition indices in the bowhead whale. Blubber was heterogeneous in composition, varying by both site and depth. Sex, age-class, season and body length were all significant factors in determining lipid content (quality) of blubber. Blubber thickness (quantity) was highly correlated with body length after?9 m. Blubber lipid content at umbilicus sites and inner depths was most variable and presumably most responsive to nutritional changes. Blubber properties appeared to exceed what was necessary for insulation, further supporting the concept for the need to store energy as a consequence of the large seasonal and annual variability of food availability in the arctic environment. These data establish a baseline for long-term monitoring of bowhead whale health and population condition. Second, I addressed post-mortem changes in blubber composition of a stranded humpback whale. Lipid content decreased due to tissue decomposition by as much as 24%, limiting the ability to accurately assess nutritional status and health. Finally, in response to a growing need for validation of the use of fatty acid profiles as dietary tracers in top marine predators, I investigated the effects of prey switching on fatty acid profiles in plasma and red blood cell membranes (RBCs) of captive harbor seals. In plasma, nine of fifteen fatty acids responded significantly with prey switching, compared to only three plus one ratio in RBCs. Season and total daily lipid intake also affected the level of some plasma fatty acids. Diet was reliably predicted from fatty acid profiles in plasma after two weeks and in RBCs at four months using discriminant function analysis. Plasma and RBC fatty acid profiles provided an integration of dietary history, representing short-term and long-term 'dietary windows, ' respectively.