Thermal Budgets and Climate Spaces: The Impact of Weather on the Survival of Galapagos (Arctocephalus galapagoensis Heller) and Northern Fur Seal Pups (Callorhinus ursinus L.)

Abstract

The ability of fur seal pups to cope with diverse climatic conditions on land was investigated by constructing a thermal budget based on published physiological studies. The model was applied to northern fur seals (Callorhinus ursinus L.) breeding on the Pribilof Islands, Alaska, and on San Miguel Island, California; also to the Galapagos fur seal pup (Arctocephalus galapagoensis Heller) on the Galapagos Islands. The combinations of environmental extremes that pups can withstand during the first week of life were identified. The study concluded that a healthy, averagesized pup on the Pribilofs could have tolerated any combination of air temperature, wind speed and level of humidity recorded since the mid 1950s, but that pups with low birth weights could have succumbed during periods of cold, wet and windy weather. On San Miguel Island, the model predicts high mortalities of large pups during hot, dry weather, which suggests strong selection pressures towards the survival of smaller animals. The model further suggests that the success of the Galapagos fur seal at the equator is related to its small body size and behavioural attributes, such as seeking shade and periodically wetting its fur. Key-words: Arctocephalus galapagoensis, Callorhinus ursinus, climate space, energetics, Galapagos fur seal, northern fur seal, seal pups, thermal budget