Muscle biochemistry of a pelagic delphinid (Stenella longirostris longirostris): insight into fishery-induced separation of mothers and calves

The length of time required for postnatal maturation of the locomotor muscle (longissimus dorsi) biochemistry [myoglobin (Mb) content and buffering capacity] in marine mammals typically varies with nursing duration, but it can be accelerated by species-specific behavioral demands, such as deep-diving and sub-ice transit. We examined how the swimming demands of a pelagic lifestyle influence postnatal maturation of Mb and buffering capacity in spinner dolphins ( Stenella longirostris longirostris ). Mb content of newborn (1.16±0.07 g Mb per 100 g wet muscle mass, n =6) and juvenile (2.77±0.22 g per 100 g, n =4) spinner dolphins were only 19% and 46% of adult levels (6.00±0.74 g per 100 g, n =6), respectively. At birth, buffering capacity was 52.70±4.48 slykes ( n =6) and increased to 78.53±1.91 slykes ( n =6) once a body length of 141 cm was achieved, representing 1.6- to 2.0-year-old dolphins. Based on the age of weaning (1.3-1.6 years post-partum), muscle maturation occurred just after weaning as described for coastal bottlenose dolphins ( Tursiops truncatus ). Thus, a pelagic lifestyle does not promote rapid maturation of muscle biochemistry. Rather, it promotes enhanced muscle biochemistry: newborn and adult spinner dolphins had four- and two-times greater Mb contents than newborn and adult bottlenose dolphins, respectively. Indeed, adult levels rivaled those of deep-diving cetaceans. Nonetheless, the relatively underdeveloped muscle biochemistry of calves likely contributes to documented mother-calf separations for spinner dolphins chased by the tuna purse-seine fishery.