The robust Commerson’s dolphin, like other species of the genus, resembles the body shape of porpoises. The head is blunt, with little or no beak and a relatively straight mouthline. The dorsal fin is moderately low and rounded, rising at a shallow angle from the back; the flippers and flukes have rounded tips.
The striking coloration contrasts black and white in a complex pattern. There is a white band that completely encircles the body, from just behind the blowhole to in front of the dorsal fin, continuing ventrally from behind the flippers to the genital area. There is a large white patch on the throat, and a black oval to heart-shaped patch around the genitals that varies in shape according to gender. In females the heart-shaped patch generally points forward; while in males, the patch points backward. The rest of the animal is black, including the top of the head, flippers, dorsal fin, and flukes. Newborn animals have a muted pattern of mostly gray tones, as do many small cetaceans. Twenty-eight to 35 small, pointed teeth line each tooth row.
Length at birth ranges from 65-75 cm. Off South America, adult Commerson’s dolphins reach up to 1.5 m and 66 kg; while those off the Kerguelen Islands reach 1.75 m and 86 kg. Females are slightly larger than males in this species. The Kerguelen Islands population is apparently distinct, with these larger animals having a characteristic gray shade replacing the black and white color pattern.
Can be Confused With
The only other black and white small cetacean likely to be confused with this species is the spectacled porpoise, but the dorsal fin shape and the color pattern differences should make these two species easily discernable. In some areas, Commerson’s dolphins may also be confused with Chilean dolphins, which have a similarly-rounded dorsal fine, but are mostly dark gray and lack the black and white patterns on the dorsal surface.
Commerson’s dolphins have a localized range. There are at least two disjunct populations of Commerson’s dolphins, one located in waters adjacent to South America and the Falkland Islands, and one found in the waters of the Kerguelen Islands in the Indian Ocean. The South American population has been documented as far north as the mouth of the Rio Negro, along the Atlantic and Pacific coasts of Patagonia, in the Straits of Magellan, in the Drake Passage, and around the Falkland Islands. There are unsubstantiated reports of this species at South Georgia, but these were rejected by recent work. The Kerguelen Islands population is most commonly sighted in the Golfe du Morbihan on the eastern side of the island.
Ecology and Behavior
Commerson’s dolphin inhabit coastal waters. Small groups of less than 10 individuals are the norm for this species, although they do sometimes aggregate into groups of over 100. These are quick, active animals. They are known to ride bow waves and to engage in various types of leaps. Commerson’s dolphins prefer relatively shallow coastal waters. They often swim upside down.
The breeding season spans the austral (southern) summer, from November to February.
Feeding and Prey
Commerson's dolphins are opportunistic, feeding primarily near the bottom on various species of fish, squid, and shrimp.
The IUCN lists the Commerson’s dolphin as data deficient because too little is known about this species to evaluate its conservation status. Commerson’s dolphins have been hunted for food and crab bait in the southern parts of their range. In addition, this species is caught incidentally in several fisheries, primarily those using gillnets in coastal waters. Despite these threats, the species still appears to be reasonably numerous, and is not thought to be in danger of extinction.
Bastida, R., V. Lichtschein and R.N.P. Goodall. 1988. Food Habits of Cephalorhynchus commersonii off Tierra del Fuego, Argentina. pp. 143-160 in R.L. Brownell, Jr. and G.P. Donovan, eds. The Biology of the Genus Cephalorhynchus. Report of the International Whaling Commission, Special Issue 9.
Dawson, S.M. 2002. Cephalorhynchus dolphins: Cephalorhynchus heavisidii, C. eutropia, C. hectori and C. commersonii. pp. 200-203 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.
Dziedzic, A. and V. De Buffrenil. 1989. Acoustic signals of the Commerson’s dolphin, Cephalorhynchus commersonii, in the Kerguelen Islands. Journal of Mammalogy 70:449-452.
Goodall, R.N.P. 1994. Commerson’s dolphin Cephalorhynchus commersonii (Lacepede, 1804). pp. 241-267 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press.
Kastelein, R.A., J. McBain and B. Neurohr. 1993. Information on the biology of Commerson’s dolphins (Cephalorhynchus commersonii). Aquatic Mammals 19:13-19.