Common Dolphin

The common dolphin throughout history has often been recorded in art and literature. It was recently proposed that twoforms of this species, the short- and long-beaked common dolphin, represent two distinct species.

Common dolphins are colorful, with a complex crisscross or hourglass color pattern on the side; the long-beaked common dolphin being more muted in color. When looking at the profile of the two common dolphin species, the short-beaked common dolphin has a more rounded melon that meets the beak at a sharp angle, as compared to the long-beaked common dolphin that has a flatter melon that meets the beak at a more gradual angle.

Color patterns on the common dolphin are the most elaborate of any cetacean. The back is dark gray-to-black from the top of the head to the tail dipping to a V on the sides below the dorsal fin. The flanks are light gray behind the dorsal fin and yellowish-tan forward of the dorsal fin, forming an hourglass pattern. Its belly is white. There are large dark circles around the eyes connected by a dark line that runs across the head behind the beak and a black stripe runs from the jaw to the flippers.

The dorsal fin is triangular-to-falcate (curved). It ispointed and located near the middle of the back and is black-to-light gray in color with a black border. The flippers are long and thin and slightly curved or pointed depending on geographical location. Flukes are thin and pointed at the tips with a slight notch in the center.

Common dolphins can reach lengths of 7.5 - 8.5 feet (2.3-2.6 m) and weigh as much as 297 lb. (135 kg). The short-beaked common dolphin is relatively heavier, and has a larger dorsal fin and flippers than the long-beaked common dolphin.

The common dolphin feeds on squid and small schooling fish. In some parts of the world, common dolphins feed at night on the deep scattering layer, which moves towards the water's surface during that time. Common dolphins have been seen working together to herd fish into tight balls. Like many other dolphin species, the common dolphin will sometimes take advantage of human fishing activities (such as trawling), feeding on fish escaping from the nets or discarded by the fishermen.

Sexual maturity is reached at 3 to 4 years of age or when they reach 6 to 7 feet in length (1.8 to 2.1 m). Calves are 30 to 34 inches at birth (76 to 86 cm ); gestation period is 10 to 11 months.

The common dolphin is found in all tropical and warm-temperate waters. The long-beaked common dolphin is found more in coastal waters; the short-beaked common dolphin is found in offshore waters and is the species that occurs frequently in the eastern tropical Pacific. Both long-beaked and short-beaked common dolphins occur in the Southern California Bight.

Common dolphins are often found in large herds of hundreds or even thousands. They are extremely active, fast moving, and engage in spectacular aerial behavior. They are noted for riding bow and stern waves of boats, often changing course to bow ride the pressure waves of fast-moving vessels and even large whales. Common dolphins can be frequently seen in association with other marine mammal species.

Traditionally, hundreds of thousands of common dolphins have been taken incidentally, along with spinner and pantropical spotted dolphins, in purse seine nets used during tuna fishing operations in the eastern tropical Pacific although these numbers may be improving. Common dolphins also may be caught accidentally in other fishing gear, such as midwater trawls. Turkish and Russian fishermen used to catch large numbers of common dolphins in the Black Sea for meat (to be used for fish meal) and oil. The fishery stopped after the common dolphin numbers became severely depleted (and still is); there are several reports suggesting that the Turkish fishery may have resumed. Many common dolphins are taken in a Japanese small cetacean fishery and directly caught in the Mediterranean. Some common dolphins may be taken in Peru for human consumption.

• Evans, W.E. 1994. Common dolphin, white-bellied porpoise Delphinus delphis Linnaeus, 1758. Pages 191-224 in Handbook of Marine Mammals, vol. 5: The first book of dolphins (S.H. Ridgway and R. Harrison, eds.). San Diego: Academic Press.
• Heyning, J.E. and W.F. Perrin. 1994. Evidence for two species of common dolphins (Genus Delphinus) from the eastern North Pacific. Contributions in Science, Natural History Museum of Los Angeles County, No. 442.
• Jefferson, T.A., S. Leatherwood, and M.A. Webber. 1993. Marine Mammals of the World. FAO Species Identification Guide. Rome: FAO.
• Klinowska, M. 1991. Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. Gland, Switzerland: IUCN (World Conservation Union).
• Leatherwood, S. and R. Reeves. 1983. Whales and Dolphins. San Francisco: Sierra Club Books.

• We greatly appreciate the knowledge and assistance of Dagmar Fertl, Biologist, Minerals Management Service, U.S. Department of Interior.
• Illustrations courtesy Uko Gorter, Copyright © 2003, All Rights Reserved.