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Chilean dolphins

Description: Small, chunky and blunt-headed dolphins without beak (and therefore often wrongly called porpoises). The flippers are rounded and almost paddle-shaped. The dorsal fin is proportionally large and with a rounded, convex trailing edge, like a Mickey Mouse ear (Dawson 2002). Basically grey, with a lighter grey 'cap' over the melon. The lips are white, as is the throat and belly, and behind each flipper there is a white 'armpit'. The flippers are linked by a grey band across the throat, which is often shaped like a rhombus in the centre. Around 1.7m long, mass reaches 60 kg.

Distribution: Chilean dolphins occur in coastal waters of southern South America from Valparaiso, Chile (33°S), south to Isla Navarino, Beagle Channel, and Cape Horn, Argentina (55° 15'S; Rice, 1998). C. eutropia is restricted to cold, shallow, coastal waters. Its distribution seems to be continuous, though there seem to be areas of local abundance, such as off Playa Frailes, Valdivia, Golfo de Arauco, and near Isla de Chiloé (Dawson 2002). The species is known to enter Rio Valdivia and other rivers.The easternmost sighting of C. eutropia was near the eastern mouth of the Strait of Magellan. Although it is mostly allopatric with Commerson's dolphin, Cephalorhynchus commersonii, the ranges of the two species may overlap slightly in the Strait of Magellan and Beagle Channel, on the border with Argentina.

Population size: The total population appears to be very small (low thousands at most). Suggestions that the species is becoming very rare are worrying and impossible to refute without dedicated survey work (Dawson 2002).

Cephalorhynchus eutropia has been called a rare dolphin, but perhaps it has been seldom seen because of the lack of boat traffic and of trained observers in the channels, and because of its shy, evasive behaviour. Research in Chile has revealed that it may be locally abundant in areas such as Valdivia, the Golfo de Arauco and near Chiloé, where groups of 20-50 or more animals have been seen. Certain local populations seem to be resident year round, especially near Chiloé (Goodall, 1994).

Chilean dolphins represented 16% of the cetacean sightings, captures, and strandings in an 8-year study between Coquimbo (30°S) and Tome (36°37'S). However, most sightings occurred on an opportunistic basis as few ship surveys and no aerial surveys have been carried out. There are indications that the Chilean dolphin may be fairly common.

Habitat: According to Goodall (1994) the Chilean dolphin inhabits two distinct areas: (1) the channels from Cape Horn to Isla Chiloé and (2) open coasts, bays and river mouths north of Chiloé, such as waters near Valdivia and Concepción. It seems to prefer areas with rapid tidal flow, tide rips, and shallow waters over banks at the entrance to fjords. The dolphins readily enter estuaries and rivers. Most sightings have been near shore and therefore it is considered a coastal species, although little scientific survey effort has been made in offshore waters. The Chilean dolphin is thought to occur more or less continuously throughout its range and may associate with Lagenorhynchus austratis (Goodall, 1994; Jefferson et al. 1993). Carwardine (1995) reports that they are often seen among breakers and swells very close to shore. Animals in the southern part of the range tend to be more wary of boats and difficult to approach; in the north, they have been known to swim over to boats and may bow-ride.

Schooling: The usual group size is from two to 10 dolphins and most observers have reported sighting only two or three animals at one time. Nevertheless, groups of 20-50 or more dolphins are seen at times, especially in the northern part of the range, and early investigators wrote of "great numbers". Such observations may represent occasional aggregations of smaller groups. The largest concentration ever reported was 15 miles long, possibly 4000 animals, which moved north past Queule (39°22'S), hugging the shore (Goodall, 1994).

Food: Eutropia feeds on crustaceans (Munida subrugosa), cephalopods (Loligo gahi), and fish, such as sardines (Strangomera bentincki), anchoveta (Engraulis ringens), róbalo (Eteginops macrovinus) and the green alga Ulva lactuca. Dolphins near a salmon hatchery on Chiloé played with salmon and may have eaten young released salmon.

Migration: Nothing is known of the movements or migration in this species. Numerous observations in the Valdivia area suggest that there is at least one resident pod, but individual animals have not been identified to confirm this. Sightings throughout the year in the northern part of the range (north of Chiloé) and during most months in the central and southern section have been reported.

Direct catch: Although killing of dolphins is prohibited by law, they are taken for bait, and it has been claimed that they were also used for human consumption. Fishermen in coastal areas north of Chiloe harpoon or used those taken incidentally in their nets, as bait for fish caught on long lines with many hooks, for swordfish fished with individual hooks, or for crab ring nets. From Chiloé south, and especially in the Magellan region, dolphins are taken along with penguins, sheep, seals, sealions, other marine birds, and fish for bait for the lucrative "centolla" (southern king crab, Lithodes santotta) and "centolion" (false king crab, Paratomis granutosa) fishery. The larger crab-processing companies provide bait (in insufficient quantities) for their fishermen, but independent fishermen who supply smaller companies harpoon or shoot their own bait and claim that the crab prefer dolphins over other animals and birds. It has been estimated for the 1980's that two Chilean dolphins could be taken per week per boat, and that as many as 1300-1500 dolphins are harpooned per year in the area near the western Strait of Magellan. Fishing areas since then have moved farther north and south, but the captures of dolphins for bait continue (Goodall 1994). Although hunting is now illegal, fishers in the area are poor and enforcement of the law in remote areas is practically impossible. A dependable alternative supply of inexpensive bait is needed. (Dawson 2002). The actual numbers taken remain unknown.

Incidental catch: Incidental catch probably occurs throughout its range, especially in the north, where dolphins can become entangled in several kinds of nets. No calculation has been made of the extent of incidental catch in Chile, but at Queule, near Valdivia, Chilean dolphins account for 45.8% of the dolphins taken in gill nets set from some 30 boats. This implies a catch of some 65-70 animals per year at this one port.

Remarks: This species is insufficiently known with respect to all aspects of its biology and potential threats. It is listed as "Data Deficient"..

Cephalorhynchus eutropia is included in Appendix II of the CMS (see "links"): the range of this species may extend beyond the Chilean border into Argentinean waters in the Beagle channel and at the entrance of the Strait of Magellan near Cabo Virgenes and Cabo Espiritu Santo.

Collection of by-catch and sighting data is strongly needed. In a small population of slow breeding animals, even a very low level of incidental catch can be enough to continue the decline.

Sources: Carwardine M (1995) Whales, Dolphins and Porpoises. Dorling Kindersley, London, UK, 257 pp.
- Dawson SM (2002) Cephylorhynchus dolphins. In: Encyclopedia of marine mammals (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, San Diego, 200-203.
- Goodall RNP (1994) Chilean dolphin - Cephalorhynchus eutropia (Gray, 1846). In: Handbook of Marine Mammals (Ridgway SH, Harrison SR eds.) Vol. 5: The first book of dolphins. Academic Pres, London, pp. 269-288.
- Hucke-Gaete R ed. (2000) Review on the conservation status of small cetaceans in southern South America. UNEP/CMS Secretariat, Bonn, Germany, 24 pp.
- Jefferson TA, Leatherwood S, Webber MA (1993) FAO Species identification guide. Marine mammals of the world. UNEP / FAO, Rome, 320 pp.
- Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Special Publication Number 4 (Wartzok D, Ed.), Lawrence, KS. USA.
- Ward HK (2001) Chilean Dolphin.