Grey whale (Eschrichtius robustus) COSEWIC assessment and status report: chapter 2
Eastern North Pacific population
The grey whale (Eschrichtius robustus) is a medium to large (11-15 m) baleen whale of dark grey colour. Grey whales lack a dorsal fin. The baleen plates are short and cream to pale yellow. Two to four throat grooves allow the throat to extend during feeding. The whales have mottled skin and are often covered with patches of barnacles and crustaceans.
The North Atlantic population of grey whales was extirpated in the 18th century. Today grey whales occur in two populations in the North Pacific. The western North Pacific population migrates between winter breeding grounds off southern China to summer feeding grounds in the Sea of Okhotsk. The eastern North Pacific population winters along the west coast of Baja California, Mexico. Most eastern Pacific grey whales spend the summer feeding in arctic waters of the Bering, Chukchi, and Beaufort seas, but a small portion, called the summer-resident community, feeds in temperate waters from northern California to southeastern Alaska. In Canada, feeding grounds are in the southern Beaufort Sea, as well as in the coastal waters of British Columbia.
Grey whales are usually found in shallow (< 60 m) water close to shore. The breeding lagoons are shallow, sheltered bays with relatively warm water and high salinity. On arctic feeding grounds, grey whales feed almost exclusively over mud or sand bottom and avoid areas of heavy ice. On temperate feeding grounds, they also feed over rocky bottom and in kelp beds. Summer-resident grey whales are most frequently sighted along the outer coast, but occasionally enter protected bays and inside waterways.
Grey whales reach sexual maturity at approximately 8 years and may live up to 70 years. Females give birth to a single calf in late winter in Mexico. The calf joins the mother on her northward migration and is weaned in late summer on the feeding grounds. Since the gestation period lasts 13-14 months, female grey whales usually only give birth in alternate years. Mortality of calves and yearlings is relatively high, but decreases as the animals approach sexual maturity.
On arctic feeding grounds, grey whales feed predominantly on amphipod crustaceans by scooping up sediment and straining it through their baleen. During the northward migration and on temperate feeding grounds, grey whales appear to have a more varied diet that includes herring eggs and larvae, mysid shrimps, ghost shrimps and crab larvae in addition to amphipods. Grey whales are infested with ecto- and endoparasites and are occasionally attacked by killer whales during the migration and on the feeding grounds.
Population sizes and trends
Commercial whaling reduced the size of the eastern North Pacific population to approximately 4000 individuals in the last century. Protected internationally in 1937, the population increased steadily at an annual rate of about 2.5% to an estimated size of 26 000 in 1998. This may be close to the historic abundance. The population subsequently declined and was estimated to number around 18 000 in 2002. The best estimate for the number of summer-resident grey whales off the British Columbia coast is in the low hundreds. The western North Pacific population, which spends the summer feeding in the Sea of Okhotsk, has yet to recover from commercial exploitation. This population was estimated to number 100 individuals in 2002 and is considered endangered.
Limiting factors and threats
No coordinated program to determine the cause of mortality of stranded whales is currently in place in western Canada, and information on the cause of mortality of grey whales off British Columbia is therefore limited. Industrial development of shallow marine areas (e.g. oil exploration and offshore mining) and the associated noise pollution (e.g. seismic exploration) can cause loss and deterioration of habitat. Ice cover on the arctic feeding grounds limits the feeding season and thus affects mortality and calf production. In addition, grey whales are killed by entanglement in fishing gear and in collisions with ships. A subsistence harvest of grey whales from the eastern North Pacific population managed by the International Whaling Commission appears sustainable for the population as a whole.
Special significance of the species
Grey whales may be a keystone species in arctic marine ecosystems and are responsible for recirculating nutrients from the sediments into the water column. Grey whales are of cultural importance and were historically of economic importance for the subsistence of native peoples in the Arctic and along the west coast of North America, including Canadian First Nations. Grey whales are the focus of an expanding whale-watching industry in British Columbia and are of significant economic value to coastal communities.
Existing protection or other status designations
Grey whales are internationally protected from commercial whaling, and the trade in grey whale products is prohibited by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Mexico has limited commercial activity in some of the breeding grounds of the eastern North Pacific population. Grey whales are protected by the Marine Mammal Protection Act in the United States and under the Fisheries Act and the Marine Mammal Regulations in Canadian waters, which make it illegal to hunt or disturb cetaceans except for subsistence use.
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