Gray whales (Eschrichtius robustus) off Sakhalin Island, Russia: Seasonal and annual patterns of occurrence

The annual return, seasonal occurrence, and site fidelity of Korean-Okhotsk or western gray whales on their feeding grounds off northeastern Sakhalin Island, Russia, were assessed by boat-based photo-identification studies in 1994-1998. A total of 262 pods were observed, ranging in size from 1 to 9 whales with an overall mean of 2.0. Sixty-nine whales were individually ide ntilled, and a majority of all whales (71.0%) were observed in multiple yea rs. Annual sighting frequencies ranged from 1 to 18 d, with a mean of 5.4 d . The percentage of whales reidentified from previous years showed a contin uous annual increase, reaching 87.0% by the end of the study. Time between first and last sighting of identified individuals within a given year was 1 -85 d, with an overall mean of 40.6 d. Annual calf proportions ranged from 4.3% (1997) to 13.2% (1998), and mother-calf separations generally occurred between July and September. The seasonal site fidelity and annual return o f whales to this pare of the Okhotsk Sea emphasize its importance: as a pri mary feeding ground for this endangered population.