Gray Whale

The gray whale makes the longest migration of any mammal known, each autumn and spring they pass between their Arctic summer feeding grounds and the warm lagoons near the equator where females give birth (5). This yearly round-trip may entail individuals travelling up to 20,400 kilometres (2). Sexual activity can occur at any time of the year, but tends to be concentrated on the migration south (5). Little is known about the mating strategies of this species, but various numbers of individuals can be involved (5). The breeding cycle last two years: gestation takes about 13 months and the single calf is then suckled for a further seven months (5). At birth the calf is smooth compared to the encrusted adults and lacks sufficient blubber that would allow it to survive in Arctic waters (2). The mother may have to hold the calf near the surface to help it to breathe during the first few hours after birth (2). This species is the only cetacean to feed by straining the sediment on the sea floor (5). Individuals roll onto their sides after diving to the bottom and take large amounts of sediment into their mouth. As the whale rises to the surface it strains the contents of the mouth through the baleen, leaving a trail of mud and sand behind it. The invertebrate prey consisting of bottom-dwelling crustaceans, worms and molluscs is isolated in this way and swallowed (5). A number of seabirds are attracted to feeding gray whales, and take advantage of invertebrates that escape the filtering process (2). Sufficient fat reserves are stored in the feeding grounds to allow individuals to go without food during the breeding season; on return to the feeding grounds about a third of the body weight may have been lost (5). Killer whales are the only non-human predator of the gray whale. Attacks directed towards calves have been observed; adult gray whales often try to position themselves between the killer whales and the calf in order to protect it, and they may also head for shallow waters and kelp beds to take refuge from the attackers (2).

In 1946, the International Whaling Commission (IWC) legally protected gray whales from commercial whaling, and the eastern Pacific stock has shown a remarkable recovery, increasing from the brink of extinction to around 21,000 individuals today (6). However, the western Pacific population that migrates along the east coast of Russia remains very small and Critically Endangered (1). Whale watching, particularly in southern California and Mexico, has developed into an extremely popular tourist attraction (4), allowing people to appreciate these awesome creatures in their natural environment and providing additional value to their conservation.

A giant of the ocean, the gray whale is mottled dark to light grey in colour and is encrusted with patches of barnacles and whale lice (4). The species lacks a dorsal fin and instead has a series of bumps along a dorsal ridge on the final third of the back (2). There are two deep grooves on the throat, which allow the mouth to expand when feeding, and the baleen, which is used to filter food, is cream-white in colour. When surfacing, the 'blow' produced is distinctly bushy, short and forked, or 'heart-shaped', as it comes from two blowholes (2) (5). Females tend to be larger than males but otherwise the two sexes are similar in appearance (5). Whalers referred to gray whales as 'devilfish', due to the ferocity of mothers when separated from their calves (4) (5).

This whale typically occurs in coastal waters no deeper than 100 metres (2). The eastern Pacific stock migrates annually from Arctic feeding grounds to breed in Mexican waters, whilst the western Pacific stock migrates along the east coast of Russia (6).

There are two main stocks of the gray whale; one occurs along the east Pacific coast from Baja California to the Bering and Chukchi seas, the other occurs in the west Pacific from South Korea to the Okhotsk Sea (2). The gray whale once also occurred in the Atlantic Ocean, but became extinct here in the late 17th to early 18th century (5).

Classified as Least Concern (LC) on the IUCN Red List (1), and listed on Appendix I of CITES (3). The northeast Pacific stock is classified as Least Concern (LC), and the northwest Pacific stock is classified as Critically Endangered (CR) (1).

The main threat to this whale has been hunting; humans have exploited the species for its oil, hide, baleen and meat (6). The activities of early whalers were, at the very least, a contributing factor to the extinction of the gray whale in the Atlantic Ocean (5), while massive over-exploitation in the 19th and 20th centuries almost destroyed the whole species (6). Whilst hunting is now banned a small quota is permitted to indigenous hunters (6). Shipping and industrial activities in the coastal migratory routes increase the risk of collisions with ships, entanglement in fishing nets and pollution. Furthermore, habitat degradation resulting from drilling and dredging is also a problem (1) (5).