Gray whale (Eschrichtius robustus) at calving sites in the Gulf of California, México

Resumen

Records of gray whales (Eschrichtius robustus) at and near their two known calving sites in the Gulf of California (Sea of Cortés), México, are reviewed up to 1995. The sites of Tojahui/Yavaros (Sonora) and Bahía Santa María (Sinaloa) represented the most distant calving grounds regularly visited by the species. Prior observations (mainly in the 1950s and 1960s) revealed relatively small but seasonally consistent numbers of whales, with maximum counts, including calves, of 30 individuals at Bahía Santa María in 1954, and 17-19 at Tojahui/Yavaros in 1955, 1963 and 1971. Observations (initiated in 1979) as well as interviews with longtime local residents and fishermen, document a decline in numbers and occupancy times of whales, especially cow/calf pairs, visiting these sites. In contrast, 19th century whaling records indicate that many more gray whales were found seasonally along these coasts. The recent decline, leading to the apparent disappearance, is likely to be due to human-induced disturbances related to accelerated regional socio-economic development, with associated increases in artisanal and industrial fishing activities and other forms of maritime traffic. Within less than four decades of their ‘discovery’, it appears that no gray whales have returned to calve at these sites since the mid-1980s. Barring an unlikely change in regional fishing practices, this apparent abandonment of calving sites on the northwest coast of mainland México suggests that any anticipated further increase in population size of the eastern North Pacific stock may be unwarranted