Commerson'S Dolphin

=== Cephalorhynchus commersonii commersonii ===

The commersonii subspecies has a black head, dorsal fin, and fluke, with a white throat and body. The demarcation between the two colours is very clear-cut. This stocky creature is one of the smallest of all cetaceans, growing to around 1.5 m (5 ft). A mature female caught off of southern Patagonia, at 23 kg (51 lb) and 1.36 m (4.5 ft), may be the smallest adult cetacean on record. Its appearance resembles that of a porpoise, but its conspicuous behaviour is typical of a dolphin. The dorsal fin has a long, straight leading edge which ends in a curved tip. The trailing edge is typically concave, but not falcate. The fluke has a notch in the middle.

Two disjunct subspecies of the dolphin are found in geographically disparate areas separated by 130° of longitude and about 8,500 km (5,300 mi); it is not known why they are thus distributed. Global populations are unknown, but the species is accepted to be locally common.

The main subspecies, C.c.commersonii, is found inshore in various inlets in Argentina including Puerto Deseado, in the Strait of Magellan and around Tierra del Fuego, and near the Falkland Islands. A survey in 1984 estimated there to be 3,200 individuals in the Strait of Magellan.

Dolphins of the second subspecies, C.c.kerguelenensis, were discovered in the 1950s. They reside near the Kerguelen Islands, in the southern part of the Indian Ocean, and prefer shallow waters.

Commerson's dolphin is very active. It is often seen swimming rapidly on the surface and leaping from the water. It also spins and twists as it swims and may surf on breaking waves when very close to the shore. Furthermore, it will bow-ride and swim behind fast-moving boats. It is also known to swim upside-down, which is thought to improve the visibility of its prey.

This dolphin feeds on a mix of coastal and pelagic fish and squid. Those in the South American subpopulation supplement their diets with crustaceans. Individuals have been recorded as entering the Santa Cruz River to forage there during low tide.

They can be found in estuaries, especially during the breeding season.

The IUCN lists Commerson's dolphin as Least Concern in its Red List of Threatened Species. The proximity of the dolphin to the shore makes accidental killing in gillnets a common occurrence. The dolphin was killed for use as crab bait by some Argentinian and Chilean fishermen in the 1970s and 1980s, but this practice has since been curtailed.

The Commerson's dolphin population of South America is listed in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). This is because it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.