Myoglobin Distribution in the Locomotory Muscles of Cape Fur Seals (Arctocephalus pusillus pusillus)

Diving animals rely on oxygen stored in their blood, muscles, and lungs to maintain aerobic metabolism during routine dives. This is made possible primarily by an elevated mass-specific blood volume, hemoglobin concentration, and muscle myoglobin concentration relative to terrestrial animals. In our previous studies of harbor seals and five species of cetaceans, the distribution of myoglobin in the locomotory muscles (epaxial and hypaxial muscles along the spine) was not uniform and was elevated in areas that generated greater force during swimming. In this study, we examined the fine-scale distribution of myoglobin in transverse sections of the primary swimming, or locomotory, muscles (pectoralis complex) of six male and four female Cape fur seals (Arctocephalus pusillus pusillus). The mean myoglobin concentration for all muscle samples was 36.9 +/- 5.8 mg g(-1) (range of mean values = 28.4 to 51.1). There were no significant differences in the distribution of myoglobin within and among transverse sections; however, the mean concentrations in all sections were significantly higher (p < 0.001) in females (41.6 mg g(-1) +/- 6.1) than for males (33.8 mg g(-1) +/- 2.8). The results from this study and our previous research indicate sufficient myoglobin concentrations to support an ability to store oxygen in skeletal muscles, reflecting adaptations for aerobic diving.