Gray whale

Distribution

Gray whales are found in coastal waters of the North Pacific. The greatest numbers occur along the west coast of Canada, the United States and Mexico, but small numbers are observed every year in near-shore waters of eastern Russia and Japan.

Gray whales are native or seasonally present in the following countries: Canada; China; Japan; Korea, Democratic People's Republic of; Korea, Republic of; Mexico; Russian Federation; United States

Migration

Like most baleen whales, gray whales undertake seasonal migrations between summer and autumn feeding grounds and wintering grounds in southern latitudes.  In the eastern Pacific, most gray whales feed in the Bering and Chukchi Seas, as well as the north Pacific coasts of Canada and the USA. These whales calve and mate off central and southern California, along the Baja California peninsula and in the Gulf of California.  Their  annual migration has been characterized as the longest recorded for any mammal – a round trip of up to 20,000km spanning up to 55 degrees of latitude¹.  Their migration route takes them close to shore along the west coasts of Mexico, California, Oregon, Washington, British Columbia and Alaska, where they can often be viewed from land, as well as from boats.  For many years researchers believed that the small group of gray whales that feed in eastern Russia migrate south along the Asian coast to the historical  wintering ground in southern China However, satellite tagging and photo-Identification studies have shown that many of those whales migrate across the Pacific Ocean to and from the wintering grounds in Mexico ^2,3. 

During the 6-7 months that whales are on their wintering grounds, they primarily fast, breaking down stored fat for energy.  They can lose 16-30% of their body mass during this time before returning to the summer feeding grounds. Each year, roughly 0.5% of the eastern gray whale population is thought to forgo the migration and stay on the feeding grounds near the Aleutian Islands to feed.¹

Biology and Ecology

Feeding

Gray whales feed on a variety of small crustaceans – including larval crabs and mysid shrimps⁴. They have been documented to feed on small clams in shallow muddy bays, or fish larvae in the water column, but their most common prey are small flea-like crustaceans called amphipods.  Gray whales can suction or skim feed in mid-water or near the surface but are mostly bottom feeders, where they find tube-dwelling and burrowing amphipods.  Gray whales can leave excavated trails or furrows in the sediment where they have been feeding. A gray whale can eat as much as 1,200 kg of food a day¹. Interestingly, over 90% of whales fitted with tags that measured their diving behaviour and orientation under water showed a preference for rolling onto their right sides while they feed⁵.

Reproduction and growth

Gray whales have a promiscuous mating system, with both males and females potentially mating with several partners in the same season.  Mating begins in late autumn on the migration southward and continues on the winter calving and nursing grounds.   After conception and a gestation period of 11 to 13 months, calves are born between late December and early March.  Mothers and calves are tightly bonded for 7-8 months until the calf is weaned. During this time the calf will consume as much as 1800 litres of milk a day. With a 53% fat content and 6% protein, gray whale milk is richer than that of any other known whale or dolphin species.  Mothers and calves remain close to shore during the northward migration (usually within 200m of the coast), possibly trying and avoid killer whale attack.  Mothers are very protective, sometimes fighting to the death to thwart attacks on their calves.

Research, threats and conservation status

Individual gray whales can be recognised over time through the mottling and colour patterns on their flanks below the dorsal fin as well as the patterns, scarring and serrations on the trailing edges of their tail flukes. These photos are used to monitor individuals’ movements over time and possible links between feeding and wintering grounds from one year to the next.³

Genetic sampling and satellite telemetry (the attachment of small devices that send the whale’s geographical positions to satellite receivers) allow researchers to track whale movements and have been very important for understanding the possible connections between eastern and western gray whale populations^2,6.  More information about research techniques used to study whales and dolphins can be found here.

Natural Predators

The most frequent predators of gray whales, particularly calves, are killer whales.  Many gray whales bear killer whale tooth rake scars and disfigurements on their bodies – particularly on their tail flukes.  Attacks are not always fatal, but pods of killer whales regularly attack, kill and consume gray whales, especially calves, on migration as well as in summer feeding areas.

Human-induced threats

Like all whales and dolphins, gray whales are vulnerable to accidental entanglement in fishing gear.  Western gray whale feeding grounds are also squarely situated in important oil and gas fields off the coast of Russia, and as such, there is great concern about the potential impacts of oil and gas exploration and production on the Sakhalin population. 

Conservation status

Although gray whales have been legally protected from commercial whaling since the moratorium established by the International Convention for the Regulation of Whaling, a limited catch of eastern gray whales by aboriginal communities for cultural and subsistence purposes is permitted.  Most of these catches are made in Chukotka, Russian Federation, but a small portion of the IWC catch limit is allocated to the United States. 

The gray whale sub-population that feeds near Russia’s Sakhalin Island and Kamchatka Peninsula in the western Pacific is one of the smallest whale populations in the world.  Intensively hunted in the first half of the 20^th century, western gray whales are still listed by IUCN as Critically Endangered. Numbers off Sakhalin have slowly increased from an estimated 115 animals in 2004 to 174 in 2015⁷.  Although the increase gives cause for hope, the small  number of reproductive females in the population, ongoing pressures from oil and gas development near their prime feeding grounds and the risk of entanglement or entrapment in fishing gear off Japan¹ and elsewhere in Asia are of great concern for the eventual recovery of gray whales in the western Pacific.

The eastern population appeared to recover relatively quickly after protection from commercial whaling.  The population reached nearly 30,000 in 1997/98, but then dropped to roughly 18,000 following a mass mortality event in 2000-2002. Stranded and live whales observed at that time were alarmingly thin, and the mass die-off is thought to have been linked to food shortages resulting from a possibly climate –change related reduction in productivity on their feeding grounds¹ or from unusual persistence of ice cover which prevented access to primary feeding grounds⁸.  This population (which is taken to generally represent the species as a whole) is designated as Least Concern on the IUCN Red List of threatened species.

Gray whales and whale watching

Please see the IWC Whalewatching Handbook