Five of the six endangered whales found in southern California waters are baleen whales, which feed by filtering their food through fringed baleen plates. The sixth is the sperm whale, the largest of the toothed whales. Populations of all these species were sharply reduced by commercial whaling in the nineteenth and twentieth centuries, some to the verge of extinction. As a result, in 1970, seven species were listed as endangered under the Endangered Species Act.

The seventh species, the gray whale, has since recovered to what are believed to be pre-whaling levels and has recently been removed from the List of Endangered and Threatened Wildlife. The great whales are also protected throughout the world under a moratorium on commercial whaling implemented by the International Whaling Commission in 1986.

Endangered baleen whales, including the blue, fin, sei, humpback, and right whales, are distributed worldwide in polar and temperate waters and migrate between warmer waters used for breeding and calving in winter and high-latitude feeding grounds where food is plentiful in the summer. The sperm whale is an open-water species and is found mainly in temperate to tropical waters in both hemispheres.

Although there is some variation among species, the typical baleen whale reproductive cycle involves about one year of gestation, followed by a 6- to 9-month nursing period. Females generally calve every 2 to 3 years.

Sperm whale calves are normally born in the summer or fall after a 14- to 15-month gestation period and are weaned later, at about 2 years of age. Sperm whale females generally give birth at 3- to 5-year intervals. Most baleen whales feed on a variety of shrimplike invertebrates, and some species also take small schooling fishes and squid. Sperm whales are deep divers and feed mainly on large squid and deepwater fishes.

Blue whales are the largest of all animals. They usually reach peak abundance off southern California in June and are rarely sighted after October. The blue whale migration pathway through this area generally appears as a broad band along the continental slope west of the Channel Islands. Commercial whaling reduced the blue whale population worldwide from an estimated 228,000 to less than 10,000. Currently, the blue whales that feed off California are believed to number about 2,300, more than recent estimates for the entire North Pacific population.

Fin Whales, like blue whales, migrate northward from subtropical calving and wintering grounds to summer feeding grounds in Alaska. In southern California waters, most fin whales are observed between March and October. The world population of fin whales may have been as high as 500,000 animals before their exploitation by commercial whalers began. By 1976, when they were protected from commercial harvest, the world fin whale numbers had declined to an estimated 120,000. Recent estimates for the eastern North Pacific range between 8,000 and 11,000 animals.

Sei whales are primarily an open-ocean, temperate-water species. In the eastern North Pacific, sei whales migrate northward from calving and wintering grounds in temperate and subtropical waters to summer feeding grounds that extend from the Channel Islands to Alaska. The winter range stretches from southern Mexico to central California, but sei whales are uncommon in California waters. Sei whale numbers were reduced from an estimated world population of 256,000 to about 50,000. The North Pacific population is currently estimated at 7,000 to 13,000 whales.

Humpback whales in the eastern North Pacific range from arctic waters south to California in the summer. Humpback whales winter and calve in three areas: waters off Mexico; Hawaii; and the Marianas, Bonin, and Ryukyu Islands and Taiwan in the western Pacific. In recent years, humpbacks have occurred in increasing numbers off southern California. The pre-exploitation world population has been estimated at about 115,000 animals. The world population is presently estimated at 10,000 whales, and recent estimates of the North Pacific population range from 1,200 to 2,100. About 900 humpback whales forage in California waters.

Northern right whales are the rarest of the endangered whales. In the North Pacific, the population is currently believed to number 100-200 animals, which is far below the estimated pre-exploitation size of 15,000. Right whales apparently migrate from high-latitude feeding grounds toward more temperate waters in the fall and winter. The location of calving grounds is unknown; summer feeding grounds may generally stretch across the North Pacific from the latitude of about British Columbia to the Bering Sea.

Sperm whales now number more than 1,000,000 worldwide, down from an estimated pre-exploitation population of 2,400,000. The eastern North Pacific population is currently estimated at 550,000 animals, and the species is under consideration for removal from the List of Threatened and Endangered Species. Sperm whales are primarily a pelagic species, and are generally in deep waters well offshore. In the North Pacific, females and juveniles generally remain south of about central Oregon year-round, while adult males range northward as far as the Bering Sea in summer. Off California, sperm whales are present in offshore waters year-round.

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