Meeting Abstract
105.2 Thursday, Jan. 7 Development of oxygen stores and muscle in Northern fur seals (Callorhinus ursinus): limits on juvenile foraging ability? SHERO, M.R.*; LESTYK, K.C.; ANDREWS, R.D.; BURNS, J.M.; St. Mary’s College of Maryland; University of Alaska, Anchorage; Alaska SeaLife Center; University of Alaska, Anchorage mrshero@smcm.edu
Northern fur seal (Callorhinus ursinus) population numbers have been declining, perhaps due to limited foraging ability of juveniles. Since a marine mammal’s proficiency at exploiting prey resources in a hypoxic environment is based on the ability to store large amounts of oxygen (O2) and to utilize these reserves efficiently, this study was designed to determine if juvenile Northern fur seals (NFS) had lower blood, muscle, and total body O2 stores than adults. Pups (<1 month old) were found to have calculated aerobic dive limits ~40% those of adult females primarily due to lower blood and, to a much greater extent, muscle O2 stores. Development of the Pectoralis (Pec) and Longissimus dorsi (LD) muscles was further examined by determining their myosin heavy chain (MHC) composition and enzyme activities. In all animals, the oxidative MHC I and IIA fibers were dominant, but adult muscles contained significantly more (Pec: ~150%; LD:~350%) fast-twitch oxidative-glycolytic MHC IID/X protein than pup muscles. This suggests that adults have greater ability to generate muscle power rapidly and/or under anaerobic conditions. Pup muscles also had lower aerobic and anaerobic ATP production potential, as indicated by lower metabolically-scaled citrate synthase, β-hydroxyacyl CoA dehydrogenase, and lactate dehydrogenase activity (all P values <0.001). In combination, these findings support the hypothesis that juveniles are biochemically and physiologically limited in their diving capabilities relative to adults. This may contribute to lower first year survival.
