DEVELOPMENT OF MUSCLE DIVING PHYSIOLOGY IN MARINE MAMMALS

Pinniped muscle development tracks life history such that species with short maternal dependency periods attain greater proportions of adult myoglobin levels earlier in life than species with protracted dependency periods. To determine if a similar pattern exists for mammals that develop at sea, the development of muscle myoglobin and acid buffering capacity due to non‐bicarbonate buffers was measured in the longissimus dorsi of harbor porpoise (Phocoena phocoena) and compared to data from bottlenose dolphins (Tursiops truncatus). The life history patterns of these species differ, with weaning occurring at 1 and 2.5–5 year(s) postpartum for porpoise and dolphins, respectively. Similar to dolphins, porpoise calves (n = 3) had significantly lower myoglobin content (0.8 ± 0.1 g myoglobin/100 g wet muscle mass) and acid buffering capacity (52.5 ± 0.1 slykes) than adult (n = 4) conspecifics (myoglobin: t = 4.9, P = 0.005; acid buffering capacity: t = 3.8, P = 0.013). However, the level of muscle maturity in porpoise and dolphin calves that were proportionally the same relative to adult length (50%) varied. Porpoise calves had 33% and 72% of mature myoglobin content and acid buffering capacity, respectively compared to only 10% and 65%, respectively for dolphin calves. Like pinnipeds, interspecific differences in muscle maturation in cetaceans track maternal dependency periods. Funded by NOAA NWFSC.