Body Temperature in the Northern Fur Seal, Callorhinus ursinus

Statistically significant samples of the body temperature of large wild mammals are ordinarily almost impossible to obtain. In the case of the northern (Alaska) fur seal, however, a sample of almost any desired size can be secured if one uses the animals involved in the annual commercial kill. Body temperatures of fur seals are of interest not only because of the large samples available but because of the species' size (up to 600 pounds), its high degree of specialization for an aquatic mode of life, and the fact that it lives in an environment where heat stress, in the usually accepted sense, is nonexistent. For any marine mammal the problem of heat loss to the water is always acute. Even at the extreme southern limit of the northern fur seal's winter range the difference between body temperature and environmental temperature is 20°C. or more. During much of their aquatic existence many of the adults operate in waters averaging only a few degrees above zero C. The insulation of hair and blubber necessary for the maintenance of body temperature while in the water presents a considerable physiological problem when the animals participate in violent and prolonged activities on shore during the breeding season, even though their rookeries in the Pribilof Islands are characterized by almost continuous summer overcast and air temperatures rarely rising above 12°C. Acknowledgments .—This work was carried out in the Pribilof Islands during the summer of 1951 in collaboration with the United States Fish and Wildlife Service under the general sponsorship of Dr. Victor B. Scheffer. Mr. Clarence Olson and Mr. Charles H. Anderson made available the facilities of St. Paul Island and gave every possible cooperation. Mr. Karl Kenyon assisted in obtaining the temperatures from the pups and from some of the adult bulls and cows. Methods …