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Recovery Strategy for the Grey Whale (Eschrichtius robustus), Atlantic Population, in Canada

Background

Species Assessment Information from COSEWIC[1]

Species Assessment Information from COSEWIC
 Date of Assessment:  May 2000
Common Name (population): Grey whale - Atlantic population (French: “baleine grise”) 
Scientific Name: Eschrichtius robustus, Liljeborg 1861  
 COSEWIC Status:Extirpated
Reason for designation:Extirpated apparently by human hunting, before the end of the nineteenth century 
 Canadian Occurrence:Atlantic Ocean  
COSEWIC Status History:  Extirpated before the end of the 1800s. Designated extirpated in April 1987. Status confirmed in May 2000. May 2000 assessment based on new quantitative criteria applied to information from existing 1987 status report. 

 

Description

The grey whale is a medium to large-sized mysticete (baleen) whale.  Adult females typically range from 11.7 to 15.2 m in length, while adult males are somewhat smaller at 11.1 to 14.3 m.  The grey whale is the only large baleen whale in which the upper jaw extends beyond the lower.   Grey whales lack a dorsal fin, but have a low hump and a series of seven to 15 knobs (“knuckles”) along the dorsal ridge.  Skin colour ranges from dark to light grey with various degrees of mottling, and animals often bear barnacles or barnacle scars as well as patches of whale lice.  Grey whales have two to four throat grooves (pleats that allow the throat region to expand during feeding).    

The grey whale has a variety of distinctive characteristics and accordingly is placed in the monotypic family Eschrichtiidae, separate from all other whales.

Pacific grey whales continue growing to about 40 years of age and may have a maximum age around 70 years.  Mean age at sexual maturity is 6-8 years for both sexes.  Courtship and mating occur on the southern wintering grounds, and calving and early rearing occur in shallow protected lagoons and bays on the wintering grounds.  Gestation time is about 14 months, and most females give birth to a single calf in alternate years.  Lactation continues for 6 months.   Grey whales feed primarily on benthic amphipods which they filter from bottom sediments on the northern summering grounds, but there is evidence for opportunistic feeding including planktonic crustacea and young fishes.  There is evidence of reduced feeding during the winter migration.

Populations and Distribution

Grey whales are restricted to the northern hemisphere and historically were found in the North Atlantic and North Pacific.  Currently the species is only extant in the North Pacific where two populations are found.  The eastern Pacific population, which has rebuilt to high abundance after being reduced by whaling, migrates between wintering areas on the coast of Mexico and California to summer feeding areas in the Bering, Chukchi and Beaufort Seas.  A few individuals form “summer resident” populations between northern California and southern Alaska.  The western Pacific population is little known and probably has been reduced to around 100 individuals by historical whaling.  These animals move along the coasts of China, Korea and Japan.

Grey whales occurred both in the eastern North Atlantic (at least in the Baltic Sea, North Sea, English Channel and off Iceland but probably much more widely) and in the western North Atlantic, but became extirpated probably due to harvesting during the 18th century.

Distribution in the western North Atlantic, and in Atlantic Canada, is inferred based on the distribution of subfossil remains, historical observations of whaling captains, and the distribution and migratory behaviour of the extant eastern Pacific population.  Ten subfossil specimens have been found between Long Island, New York and Ste. Lucie inlet in southeastern Florida.  As well, references to the “scrag” whale in historical whaling records, interpreted to refer to the grey whale, are known from New England.  Based on the fossil information and behaviour of the Pacific population, western Atlantic grey whales may have used shallow lagoons and bays of southeastern Florida for breeding and calving.  By inference from the migratory pattern of the eastern Pacific population, Atlantic grey whales may have visited Canadian waters, including the Scotian Shelf, Gulf of St. Lawrence, and Grand Banks, and may even have entered Hudson Bay.

Grey whales are thought to have become extirpated from the western North Atlantic by the end of the 1800s.   Information on this population is extremely sparse but it appears that whalers were familiar with the species prior to its disappearance (thus the few records from whaling captains in the 1700s), and specialists have inferred that the population was extirpated due to harvesting.

Needs of the grey whale 

Habitat and biological needs

There is no information on the biological needs of the western Atlantic population of grey whales, which would have included individuals occurring in Canada.  Based on the behaviour of the eastern Pacific population, western Atlantic grey whales would have required productive feeding grounds in northern waters, warm protected coastal lagoons for breeding and calving in southern subtropical waters (probably southeastern Florida), and a migratory corridor, probably within a few kilometers of the shoreline, connecting these areas.  Should “summer resident” individuals have occurred in the western Atlantic, as is the case in the eastern Pacific, coastal habitat to support these individuals would have been required.

Feeding habitat on the Arctic summering grounds in the North Pacific is in shallow (less than 60 m) areas with soft bottom sediments.  In the Bering Sea grey whales are seen from 0.5 to 165 km from shore, including in shallow coastal lagoons, and tend to avoid areas of heavy ice.  High productivity of benthic amphipods would be a requirement given that these animals make up 95% of grey whale diet in northern areas.  Summer resident individuals off British Columbia also prefer nearshore shallow habitats with mud or sand bottom.  Individuals off British Columbia have also been observed feeding in kelp and eelgrass areas and might use all types of coastal habitats for feeding or other uses.  Calving lagoons in Mexico are shallow (less than 4 m), warm (15-20°C), and have sandy or muddy bottoms covered in places by eelgrass beds and mangrove swamps.

Based on these observations, grey whales are very different in their habitat requirements from other large whale species, being much more associated with coastal areas.  In particular they require very shallow enclosed inshore areas for calving, near-shore coastal areas for migration, and relatively shallow benthic environments for feeding.  

Ecological role

Pacific grey whales play an important role as a benthic predator and resuspend nutrients from benthic to planktonic marine ecosystems.  An estimate made in the 1980s suggested that eastern Pacific grey whales turned over some 9% of the available amphipod community, covering a 3500 km2 area.  Population abundance has since increased substantially.  Urination and defecation in the water column would contribute substantial amounts of nutrients of benthic origin.  Grey whales excavate depressions in the seabed during feeding and as such may play an important role in structuring bottom sediments and the communities which depend on them.

Limiting factors

No limiting factors for western Atlantic grey whales can be identified since the population is extirpated.  The principal factor limiting population growth in Pacific grey whales, as with other large whale species, is the low birth rate (on average one calf every two years for grey whales).  Other potential population limiting factors would be as in the “Threats” section below. 

Threats

Description of potential threats

No detailed classification of current threats is possible since the population is extirpated, but potential threats would be similar to those for other large whale species such as the North Atlantic right whale, northern bottlenose whale, or blue whale: entanglement in fishing gear, vessel collisions, acoustic pollution from seismic surveys or other underwater activities, and the bioaccumulation of chemical contaminants.  Harvesting would not be a potential threat, since the harvesting of large whales is no longer permitted in Canada and the northwest Atlantic, other than the small Aboriginal subsistence harvests of minke whales in Greenland and bowhead whales in northern Canada (harvesting of small cetaceans such as belugas is permitted for Aboriginal subsistence).  Ship collisions and entanglement in fishing gear are known to cause mortality of large whales in Atlantic Canada, and acoustic and chemical pollution are probably degrading whale habitats. 

Information on some of the parasites and diseases of grey whales is known, but little knowledge exist of other important pathogens (bacteria and viruses). Potential health threats to the recovery of re-introduced grey whales in the Atlantic may be the spread of disease for which they have no natural immunity from a translocated animal, especially to wild populations already at risk (Measures 2004). Another potential health threat may be toxic algal blooms, given that toxic algal blooms occur in the Atlantic, particularly in coastal areas and with increasing frequency (Moore et al. 2001).



[1]All of the material in this section, except the species information from COSEWIC (Section 1.1), is drawn from Reeves and Mitchell (1987).