Myoglobin in pelagic small cetaceans

Although myoglobin (Mb) is considered to contribute significantly to the ox ygen and diving capacity of marine mammals, few data are available for ceta ceans, Cetacean by-catch in the tuna driftnet fisheries in the Sulu Sea, Ph ilippines, afforded the opportunity to examine Mb content and distribution, and to determine muscle mass composition, in Fraser's (Lagenodelphis hosei ) and spinner (Stenella longirostris) dolphins and a pygmy killer whale (Fe resa attenuata). Age was estimated by body length determination. Stomach co ntents were analyzed for the presence or absence of milk and solid foods. I t was hypothesized (a) that Mb concentration ([Mb]) would be higher in Fras er's and spinner dolphins than in other small cetaceans because of the know n mesopelagic distribution of their prey, (b) that [Mb] would vary among di fferent muscles according to function during diving, and (c) that [Mb] woul d increase with age during development. The results were as follows. ii) My oglobin concentrations of the longissimus muscle in adult Fraser's (6.8-7.2 g 100 g(-1) muscle) and spinner (5-6 g 100 g(-1) muscle) dolphins and in a n immature pygmy killer whale (5.7 g 100 g(-1) muscle) were higher than tho se reported previously for small cetaceans, (2) [Mb] varied significantly a mong the different muscle types in adult dolphins but not in calves; in adu lts, swimming muscles had significantly higher [Mb] than did non-swimming m uscles, contained 82-86 % of total Mb, and constituted 75-80 % of total mus cle mass. (3) Myoglobin concentrations in Fraser's and spinner dolphins inc reased with size and age and were 3-4 times greater in adults than in calve s, The high Mb concentrations measured in the primary locomotory muscles of these pelagic dolphins are consistent with the known mesopelagic foraging behaviour of Fraser's and spinner dolphins and suggest that the pygmy kille r whale is also a deep-diving species. The high Mb concentrations in epaxia l, hypaxial and abdominal muscle groups also support the primary locomotory functions suggested for these muscles in other anatomical studies. As in o ther species. the increase in [Mb] during development probably parallels th e development of diving capacity.