THE METABOLIC CHARACTERISTICS OF THE LOCOMOTORY MUSCLES OF GREY SEALS(HALICHOERUS-GRYPUS), HARBOR SEALS (PHOCA-VITULINA) AND ANTARCTIC FURSEALS (ARCTOCEPHALUS-GAZELLA)

It is not known precisely how marine mammals are able to maintain musc le function during active swimming in breath-hold dives, when ventilat ion stops and heart rate falls. Examination of muscle biochemistry and histochemistry can provide information on the relative importance of different metabolic pathways, the contractile potential of the muscle fibres, the oxygen storage capacity of the muscle and the capillary di stribution in these animals. In this study, samples of locomotory musc le were taken from wild grey seals (Halichoerus grypus), harbour seals (Phoca vitulina) and Antarctic fur seals (Arctocephalus gazella); Wis tar rat muscle was analysed for comparative purposes. Activities of ci trate synthase and beta-hydroxyacyl CoA dehydrogenase were higher in t he harbour seal muscle than in the grey seal muscle, suggesting that h arbour seals have a greater aerobic capacity. Both phocid muscles had a greater reliance on fatty acid oxidation than the fur seal or rat mu scles. The myoglobin data demonstrate that the grey seals have the hig hest oxygen storage capacity of the three pinniped species, which corr elates with their greater diving ability. Myoglobin levels were higher in all three pinniped species than in the Wistar rat. The fibre type compositions suggest that the muscles from the fur seals have higher g lycolytic capacities than those of the phocid seals [fur seal pectoral is, 7% slow-twitch oxidative fibres (SO), 25% fast-twitch oxidative gl ycolytic fibres (FOG), 68% fast-twitch glycolytic fibres (FG); grey se al 57% SO, 5% FOG, 38% FG; area per cents]. However, the pectoralis mu scle of the fur seal, although the most glycolytic of the pinniped mus cles studied, has the highest capillary density, which indicates a hig h capacity for fuel distribution. These results show that, while pinni ped muscle has an increased oxygen storage potential compared with the muscle of a typical terrestrial mammal, there are no distinct adaptat ions for diving in the enzyme pathways or fibre type distributions of the pinniped muscle. However, the muscle characteristics of each speci es can be related to its diving behaviour and foraging strategy.