DIVING BEHAVIOR IN RELATION TO AMBIENT WATER TEMPERATURE IN NORTHERN ELEPHANT SEALS

Our aim was to describe changes in ambient water temperature during th e course of migration by northern elephant seals (Mirounga angustirost ris) and to examine evidence for the seal using abrupt temperature gra dients for locating prey. During migration in the post breeding season , the diving patterns of 10 adult females and 7 breeding-age males fro m Ano Nuevo, California, were recorded with time-depth recorders in 19 89-1991. Recorded sea surface temperatures declined from 11-13 degrees C to a low of 3-9 degrees C as the seals moved north and increased as they returned. Depth of diving was not closely linked to sharp therma l gradients. A thermocline was evident only at the beginning and end o f the migration in less than 100 m of water, where less than 2% of div ing takes place. There were sex differences in the temperature range a t the depths where 75% of diving and foraging occurred, owing in part to habitat separation. The temperatures were lower and the range narro wer for females (4.2-5.2 degrees C at 388-622 m) than for males (5.3-6 .0 degrees C at 179-439 m). We conclude that the northern elephant sea l habitat does not provide abrupt changes in temperature that might se rve as important cues for locating prey.