Activity budgets and diving behaviour of gray whales (Eschrichtius robustus) in feeding grounds off coastal British Columbia

Behavior and diving patterns of summer resident gray whales (Eschrichtius robustus) foraging on mysids were studied in coastal bays along the north shore of Queen Charlotte Strait, British Columbia, Canada. In this region, gray whales feed primarily on planktonic prey in the water column rather than on the benthos as in their better-studied primary feeding areas. During the summers of 1999 and 2000, whales spent most of their time actively feeding or searching for prey (77%), whereas only 15% of their time was spent traveling and 8% socializing. The majority of the dives were short; the median dive duration was 1.73 min with 2 respirations per surfacing and 13 sec between blows. Whales dove frequently, spending only 11% of their time at the surface with an overall blow rate of 1.09 per minute. Activity states were characterized by significantly different diving and respiratory parameters; when feeding, whales made shorter dives, respired fewer times during a surfacing, with shorter blow intervals, and spent less time at the surface compared to traveling or searching whales. This diving pattern differs from benthic-feeding whales and likely optimizes capture of the mobile mysid swarms in shallow waters.