Scientific Classification

Common Name

Commerson's Dolphin

Kingdom

Animalia

Phylum

Chordata

Class

Mammalia

Order

Cetacea

Family

Delphinidae

Genus Species

Cephalorhynchus commersonii
Two subspecies are recognized: C. c. commersonii in southern South America and C. c. kerguelenensis in the Kerguelen Islands. The Kerguelen subspecies was apparently founded by a few individuals as recently as 10,000 years ago.

Fast Facts

Description

Commerson's dolphins are a small and very distinctive species with mostly black on the head, fin and flipper regions and mostly white in the other areas of the body. Young Commerson's are usually brown or black and gray for the first four to five months. The dorsal fin is small and rounded at the tip and the beak is small or unnoticeable.
Female:  In this species, females are typically larger than males.

Size

These are one of the smallest dolphins reaching lengths of up to 1.2 to 1.7 m (3.9 to 5.6 ft.). Females are typically larger than males. Newborn calves are approximately 55 to 65 cm (21.7 to 25.6 in.) in length.

Weight

Commerson's dolphins can reach weights of up to 35 to 60 kg (77 to 132 lbs.). At birth, calves average 4.5 to 5.5 kg (10 to 12 lbs.).

Diet

Commerson's Dolphins in South America appear to be opportunistic, feeding on various pelagic and bentho-pelagic species of fish, cephalopods, crustaceans, and benthic invertebrates in coastal waters but also on pelagic schooling fish in more open areas. In the Kerguelen Islands, they seem to have a more restricted diet, consisting mostly of semi-pelagic fishes (e.g. Champsocephalus gunnari) and to some extent benthic fishes.

Incubation

Gestation lasts a maximum of approximately 12 months.

Estral Period

Between late winter and early spring

Nursing Duration

Unknown; at least 4 or more months

Sexual Maturity

5 to 8 years

Life Span

15 to 18 years

Range

From the tip of South America (Peninsula Valdes to Tierra del Fuego), through the Strait of Magellan, around the Falkland Islands and the Kerguelen Islands. There are two populations of Commerson's dolphins; the population off the coast of southern South America and another population found around the Kerguelen Islands, which is considered a distinct subspecies. The two subspecies of Commerson’s Dolphins are separated by 130° of longitude and about 8,500 km or 5,270 miles.

Habitat

Commerson's Dolphins are found in cold inshore waters along open coasts, in sheltered fjords, bays, harbors and river mouths, and occasionally in the lower reaches of rivers.

Population

Global: Commerson's Dolphins seem to be the most abundant species of the genus Cephalorhynchus although much of its range has not been surveyed and there are only a few estimates of abundance

Status 

IUCN: Least concern; the Kerguelen subspecies is currently listed as Endangered in the regional IUCN Red List for French Southern Territories
CITES: Appendix II
USFWS: Not listed

Fun Facts

1. Commerson's dolphins typically eat 3.5 to 6 kg (8 to 13 lbs.) of food per day. This is proportionally a much greater amount than either killer whales or bottlenose dolphins ingest each day, and is due to their metabolic rate that is two to three times higher than many other whale or dolphin species.
2. The first Commerson's dolphin calf ever born in a marine zoological environment was born at SeaWorld San Diego on February 21, 1985. The calf weighed approximately 9 kg (20 lbs.) and measured 61 cm (2 ft.).
3. Commerson's dolphins are fast and highly maneuverable cetaceans regularly swimming at speeds of 11 to 13 kph (7 to 8 mph). These dolphins are commonly seen wave-riding in the bows or wakes of high-speed boats, shoreline breakers or groundswells.
4. Commerson's dolphins are typically found alone or in small groups of 2 to 3 animals and occasionally spotted in larger groups of 20 to 30 or more dolphins. They often hunt cooperatively either encircling fish and taking turns passing through to feed on the clustered fish or even driving fish onshore and temporarily stranding themselves to snatch up the fish.
5. To learn more about Commerson's Dolphin, explore the Commerson's Dolphin Infobook.

Ecology and Conservation

Feeding behavior and group size depend on the habitat type. Group size may reach one hundred individuals when the dolphins are feeding on schooling pelagic fish. When they are feeding in tidal areas in front of small rivers, in kelp forests and in waters influenced by river discharge, they are more typically alone or in small groups.

Within their range, Commerson's dolphins are considered fairly common. However, some are inadvertently caught and killed in fishing nets throughout part of their range, especially off the coast of Argentina. In the past, local fishermen intentionally caught these dolphins for food, oil or bait. Now that this practice is illegal, the rate of hunting for Commerson's dolphins has allegedly declined. Yet, it is not known how much accidental catch or entanglement in fishing gear continues to affect population numbers. YIn some parts of their range, Commerson's dolphins have been found with elevated levels of industrial pollutants, which may also pose a threat to population numbers.

As with other species of cetaceans, international laws protect Commerson's dolphins.

Bibliography

Jefferson, T.J. Leatherwood, S. and M.A. Webber. FAO Species identification Guide. Marine Mammals of the World. Rome. FAO, 1993.

Leatherwood, Stephen, and Reeves, Randall R. The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books, 1983.

Nuzzolo, D. The Commerson's Dolphin Story. San Diego. Sea World, Inc. 2004.

Reeves, R. R., Stewart, B.S., Clapman, P.J., and J.A. Powell (Peter Folkens illustrator). National Audubon Society: Guide to Marine Mammals of the World. New York: Random House, 2002.

University of Michigan – Department of Zoology – Animal Diversity Web. http://animaldiversity.ummz.umich.edu

Crespo, E., Olavarria, C., Dellabianca, N., Iñíguez, M., Ridoux, V. & Reeves, R. 2017. Cephalorhynchus commersonii (errata version published in 2018). The IUCN Red List of Threatened Species 2017: e.T4159A128963283. . Downloaded on 02 October 2018.