Migratory destinations of humpback whales wintering in the Mexican Pacific

The migratory destinations of humpback whales that winter off the Pacific coast of Mexico were examined using photo-identification. Fluke photographs taken between 1983 and 1993 from the three main whale aggregations in this area (383 from the Mainland coast; 471 from Baja California Peninsula; and 450 from Revillagigedo Archipelago) were compared with collections from all known summering grounds in the North Pacific (593 off California-Oregon-Washington; 48 off British Columbia; 429 off Southeastern Alaska; 141 off Prince William Sound; and 133 from the western Gulf of Alaska ). The migratory movements of these whales were clearly non-random. The results of the photographic comparisons and the statistical tests show clear evidence for preferred migratory destinations of humpback whales from Mainland and Baja California to California-Oregon-Washington and British Columbia summering regions. Nevertheless, differences in whale abundance estimates between these summering and wintering aggregations indicate the presence of some unsampled summering region(s). The principal migratory destination was not detected for the Revillagigedo region, although matches were found with all the summering regions sampled. This supports the hypothesis that the humpback whales from Revillagigedo are separate from the ‘American stock’. Based on the known abundance estimates, historical whaling records and genetic structure of the populations, it is proposed that historical feeding grounds off the Aleutian Islands and/or the Bering Sea are the main summer destinations of the whales from Revillagigedo.