Pabst, D.A.*; Koopman, H.N.; Rommel, S.A.; Potter, C.W; Read, R.J.; McLellan, W.A.: Ontogenetic allometry and body composition of harbor porpoises Phocoena phocoena from the western north Atlantic

North Atlantic harbor porpoises face considerable energetic challenges, as they are relatively small mammals with an intense reproductive schedule and a cold-water habitat. We describe post-natal growth of porpoises using ontogenetic allometry and body composition techniques. Our sample contained robust calves, immature, and mature porpoises (n=122) killed in fishing operations from 1992-98. Total mass and masses of 26 body components were measured using a standard dissection protocol. Most body components grew similarly in female and male porpoises. Blubber, brain and skull grew negatively allometrically; muscle and reproductive tissues grew positively allometrically. Female heart, liver, intestines and mesenteric lymph node grew significantly faster than in males. Male locomotor muscle and pelvic bones grew significantly faster than in females. High growth rates for visceral and reproductive organs in porpoises, relative to other mammals, may underlie their early maturation and support their annual reproductive schedule. Relative to other cetaceans, porpoises invest a larger percentage of their body mass in blubber. This large investment in blubber, which is highest in calves (37% of body mass), may provide small-bodied porpoises the thermal insulation required to live in cold, north Atlantic waters. The factors influencing growth rates and differential investments in body composition, thus, appear to change at various stages of a porpoise’s life. Energetic investment in porpoises shifts from an emphasis on developing an insulative blubber layer in young animals to preparing the body for reproduction by the point of maturity.