Meeting Abstract

23.5  Friday, Jan. 4  The Development of Muscle Biochemistry in a Diving Marine Endotherm, the Harbor Porpoise (Phocoena phocoena) NOREN, Dawn P.*; NOREN, Shawn R.; NOAA Fisheries, Northwest Fisheries Science Center; University of California, Santa Cruz dawn.noren@noaa.gov

Skeletal muscles of marine mammals must support the metabolic demands of exercise during periods of reduced blood flow associated with the dive response. Myoglobin is an important oxygen store for supporting aerobic diving while enhanced buffering capacity could support anaerobic metabolism during apnea. Yet little is known about the postnatal development of muscle biochemistry in cetaceans. To assess the development of these important adaptations in cetaceans, muscle myoglobin content and muscle acid buffering capacity due to non-bicarbonate buffers were measured in the longissimus dorsi of harbor porpoises (Phocoena phocoena). Muscle myoglobin and acid buffering capacity of harbor porpoise calves (body length >90 cm; n = 3) were found to be significantly lower than those of adult (body length >140 cm; n = 4) conspecifics (myoglobin: t = 4.9, P = 0.005; acid buffering capacity: t = 3.8, P = 0.013). Specifically, average myoglobin content for calves (0.8 ± 0.2 SD g myoglobin (100 g wet muscle mass)^-1) is 33% of the average adult value (2.4 ± 0.5 SD g myoglobin (100 g wet muscle mass)^-1) while average acid buffering capacity for calves (52.5 ± 0.2 SD slykes) is 72% of the average adult value (73.4 ± 9.3 SD slykes). Furthermore, myoglobin content and acid buffering capacity increase significantly with body length (range: 78 to 130 cm; n = 6) prior to adulthood (myoglobin: R² = 0.90, P = 0.004; acid buffering capacity: R² = 0.91, P = 0.004). These results demonstrate that muscle myoglobin content and acid buffering capacity develop with age in harbor porpoises. As a result, the underdeveloped muscle biochemistry of immature individuals could limit their dive performance.