Grey whale  (Eschrichtius robustus)

Grey whales are mottled dark to light grey in colour and are extremely encrusted with patches of barnacles and whale lice (4). The species lacks a dorsal fin; instead it has a series of bumps along a dorsal ridge on the final third of the back (3). 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 both blowholes (5) (3). Females tend to be larger than males but otherwise the two sexes are similar in appearance (5). Whalers referred to grey whales as 'devilfish', due to the ferocity of mothers separated from their calves (4) (5).

There are two main stocks; 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 (3). There was once a population in the Atlantic Ocean, but it was hunted to extinction about 150 years ago (6).

This whale typically occurs in coastal waters no deeper than 100 metres (3). 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 (7).

The grey 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 (3). 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 (3). The mother may have to hold the calf near the surface to help it to breathe during the first few hours after birth (3).

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 grey whales, and take advantage of invertebrates that escape the filtering process (3). 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 grey whale. Attacks directed towards calves have been observed; adult greys 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 (3).

The main threat to this whale has been hunting; humans have exploited the species for its oil, hide, baleen and meat. Massive over-exploitation in the 19th and 20th Centuries drove at least two stocks of grey whales to extinction, and almost destroyed the whole species (7). Whilst hunting is now banned a small quota is permitted to indigenous hunters (7), and an unknown level of illegal hunting still occurs (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 (6).

In 1946, the International Whaling Commission (IWC) legally protected grey 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 (7). However, the western Pacific population that migrates along the east coast of Russia remains very small and Critically Endangered (6). 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.

For more information in the grey whale see:

• The Whale and Dolphin Conservation Society (WDCS):
  www.wdcs.org
• Carwardine, M, Hoyt, E, Fordyce, R.E., and Gill, P. (1998). Whales and Dolphins. Harper Collins Publishers, London.
• The Smithsonian Institution's North American Mammals website:
  www.mnh.si.edu/mna/

Authenticated (9/10/02) by WDCS, The Whale and Dolphin Conservation Society
http://www.wdcs.org