Topographical Distribution of the Blubber of Harbor Porpoises (Phocoena phocoena)

Abstract

Thickness of blubber was measured at 48 sites on the bodies of 68 male and 46 female harbor porpoises ( Phocoena phocoena ) from the Bay of Fundy, Canada, and Gulf of Maine and mid-Atlantic coast of the United States. Blubber was thinner over the head than in the thoracic-abdominal region, where thickness varied little around the girth of the animal. Thickness of blubber anterior to the anus ranged from 15 to 25 mm. Posterior to the anus, blubber formed thick dorsal and ventral ridges but was extremely thin laterally. In the thoracic-abdominal region, blubber of calves ( X = 22.9 mm ± 3.6 SD; n = 11) was significantly thicker than that of all other animals, but lactating females had the thinnest blubber (14.5 ± 3.1 mm; n = 7). Immature porpoises of both sexes, mature males, and non-lactating mature females had thicknesses of blubber intermediate between those of calves and lactating females. Thickness of blubber anterior to the anus was correlated negatively with body size, an unusual relationship for a marine mammal. Blubber posterior to the anus was similar among reproductive classes. Blubber of the harbor porpoise appears to be divided into two functional components. The thoracic-abdominal blubber functions primarily as an energy store and insulation, and posterior blubber acts to maintain hydrodynamic shape on the peduncle. Calves and adult porpoises may have different thermoregulatory and energetic strategies, resulting in different adaptations of blubber structure.