Gray Whale

By
a gray whale's tail
Credit: Sam Beebe CC-BY

The coastal gray whale (Eschrichtius robustus) is the most often observed whale on the Pacific Coast of North America and the object of a flourishing whale-watching industry. Gray whales can be distinguished from other whales through a combination of their medium size (for a whale: 10-15m), mottled gray skin pigmentation, absence of a dorsal fin, and tendency to come quite close to shore.

The eastern Pacific Ocean population, sometimes called the California stock, calves off the coast of Baja California and most of the individual whales spend the summer feeding in the Bering and Chukchi Seas. Small numbers spend the summer feeding off southeast Alaska, British Columbia, Washington, Oregon, and California.

The western Pacific gray whale population sometimes referred to as the Korean stock, is composed of just 100 animals and is considered critically endangered. Western gray whales spend the summer feeding near Sakhalin Island. Their breeding ground is unknown but suspected to be in the waters off southern China.

Gray Whale Behavior

Feeding

Gray whales eat benthic amphipods, ghost shrimp, and a variety of planktonic crustaceans. It is the only baleen whale that habitually forages on the sea bed which it accomplishes by rolling onto one side, sucking sediments in through the lips, and using the tongue to filter the sediment through baleen plates.

Studies off the west coast of Vancouver Island indicate that gray whales shift from one type of prey species to another over the summer season depending on which is most plentiful (Darling et al 1998). Preliminary time budget observations suggest that gray whales off Vancouver Island, spend about 70% of their time feeding during the months July to September.

During the summer gray whales often feed and travel alone or in small groups. When feeding on the bottom they typically breathe 3 or 5 times in quick sequence before submerging for 3 to 5 minutes. The blow from this species appears heart-shaped from the front and rises about 1.5 m in the air.

Gray Whale Breeding Behaviour

Gray whales calve every two or three years off western Baja California. Mating is hectic with many males attempting to mate with each female in estrus.

A gray whale and her calft
A gray whale and her calft migrate north along the California coast on their way to summer feeding grounds in the Arctic. Credit: NOAA

Females come into estrus in late November and many are fertilized from that time through December. Those females that fail to conceive may come into a second estrus in January.

Males have relatively large testes which likely reflect strong sperm competition.

The fetus grows to about 4m over a year until the final month when growth slows. In late January, the pregnant females gather in shallow lagoons to give birth, Laguna Guerrero Negro, Laguna Ojo de Liebre, Laguna San Ignacio and Bahia Magdalena being the most notable nurseries. The young calf is immediately the target of ectoparasites – the barnacle Cryptolepas rhachianecti is unique to the gray whale. There are also three species of ‘whale lice’, two of which are found only on the gray whale.

Young calves are nursed for several weeks and then depart north with their mothers in May. Calves follow their mothers north in spring to the feeding grounds between northern California and the Chuckchi Sea. They become independent 7 to 9 months later. Males and females become sexually mature between 5 and 11 years of age.

References:

  1. Baird, R.W., P.J. Stacey, D.A. Duffus and K.M. Langelier. 2002. An evaluation of gray whale (Eschrichtius robustus) mortality incidental to fishing operations in British Columbia, Canada. Journal of Cetacean Research and Management 4:289-296.
  2. Bowen, W. D. and D. B. Siniff. 1999. Distribution, population biology and feeding ecology of marine mammals. Pp. 423-484 in Reynolds, J. E., III and S. A. Rommel (eds.). Biology of marine mammals. Smithsonian Institution, Washington DC
  3. Breiwick, J. W. 1999. Gray whale abundance estimates, Pp. 62 in D. J. Rugh, M. M. Muto, S. E. Moore and D. P. DeMaster. Status review of the eastern north pacific stock of gray whales. US Department of Commerce. NOAA Tech Rep. Memo NMFS-AFSC-103, Washington, D.C.
  4. Darling, J.D. 1984. Gray whales off Vancouver Island, British Columbia. Pp. 276 – 287 in The Gray Whale. M. L. Jones, S. Swartz and S. Leatherwood (eds.). Academic Press, New York, NY.
  5. Darling, J.D., Keogh, K.E., and T.E. Steeves. 1998. Gray whale (Eschrichtius robustus) habitat utilization and prey species off Vancouver Island, B.C. Marine Mammal Science 14, 692-720.
  6. Gulland, F.M.D. and others. 2005. Eastern North Pacific gray whale (Eschrictius robustus) unusual mortality event, 1999-2000. NOAA Technical Memorandum NMFS-AFSC-150.
  7. Rice, D. W. and A. A. Wolman. 1971. The life history and ecology of the gray whale Eschrichtius robustus. American Society of Mammalogists, Special Publication 3, 142 p.
  8. Wartzok, D. and D. R. Ketten. 1999. Marine mammals sensory systems. Pp. 117-175 in Reynolds, J. E., III and S. A. Rommel (eds.). Biology of marine mammals. Smithsonian Institution, Washington DC
  9. Wilson, D. E. and S. Ruff. 1999. The Smithsonian book of North American mammals. Smithsonian Institution, Washington, D.C.