Whales are aquatic mammals of the order Cetacea. The term is now applied to about 80 species of baleen whales and "toothed" whales, which include dolphins , porpoises, and non-baleen whales, as well as extinct whales. Cetaceans range from the largest known animal, the blue whale (Baleanoptera musculus ), at a length up to 102 ft (31 m) to the diminutive vaquita (Phoceona sinus ) at 5 ft (1.5 m).
Whales evolved from land animals and have lived exclusively in the aquatic environment for at least 50 million years, developing fish-like bodies with no rear limbs, powerful tails, and blow holes for breathing through the top of their heads. They have successfully colonized the seas from polar regions to the tropics, occupying ecological niches from the water's surface to ocean floor.
Baleen whales, such the right whale (Balaena glacialis ), the blue whale, and the minke whale (Balaenoptera acutorostrata ), differ considerably from the toothed whales in their morphology, behavior, and feeding ecology . To feed, a
baleen whale strains seawater through baleen plates in the roof of its mouth, capturing plankton and small fish. Only the gray whale (Eschrichtius robustus ) sifts ocean sediments for bottom-dwelling invertebrates. Baleen whales migrate in small groups and travel up to 5,000 mi (8,000 km) to winter feeding grounds in warmer seas.
The toothed whales, such as the killer whale (Orcinus orca ) and the pilot whale (Globicephala spp.), feed on a variety of fish, cephalopods, and other marine mammals through a variety of active predatory methods. They travel in larger groups that appear to be matriarchal. Some are a nuisance to commercial fishing because they target catches and damage equipment.
Large whales have virtually no natural predators besides humans, and nearly all baleen whales are now listed as endangered species , mostly due to commercial whaling . In the southern hemisphere, the blue whale has been reduced from 250,000 at the beginning of the century to its current level of a few hundred. The International Whaling Commission (IWC), which has been setting limits on whaling operations since its inception in 1946, has little power over whaling nations, such as Japan and Norway, who continue to catch hundreds of whales a year under an exemption allowing whaling for scientific research.
[David A. Duffus ]
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U.S. National Marine Fisheries Service, Humpback Whale Recovery Team. Final Recovery Plan for the Humpback Whale (Megaptera novaeangliae). Silver Spring, MD: U.S. National Marine Fisheries Service, 1991.
U.S. National Marine Fisheries Service, Right Whale Recovery Team. Final Recovery Plan for the Northern Right Whale (Eubaleana glacialis). Silver Spring, MD: U.S. National Marine Fisheries Service, 1991.