Cephalorhynchus eutropia Gray, 1846

English: Chilean dolphin
German: Chile-Delphin
Spanish: Delfín Chileno
French: Dauphin du Chili

Cephalorhynchus eutropia © Wurtz-Artescienza (see links).

1. 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, 2009). 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 1.67 m long; mass reaches 63 kg (Dawson, 2009).

2. Distribution

Chilean dolphins occur in coastal waters of the west coast 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, 2009). The species is known to enter Rio Valdivia and other rivers (Carwardine, 1995).

Distribution of Cephalorhynchus eutropia: coastal waters of Chile and southern Argentina
(Reeves et al. 2008; © IUCN; Click here for large map).

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, C. commersonii, the ranges of the two species may overlap slightly in the Strait of Magellan and Beagle Channel, on the border with Argentina (Goodall, 1994).

3. 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, 2009). C.eutropia has been called a rare dolphin, but perhaps it has been seen rarely because of the lack of boat traffic and of trained observers in the channels and because of its shy, evasive behaviour.

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 (Goodall, 1994). Overlapping with this area, and north of the Maule River (36 °N), a zone more influenced by the estuarine system, Perez-Alvarez et al. (2007) saw Chilean dolphins in 83% of the surveys . The relative abundance was significantly higher than to the south (13.6 dolphins/h versus 3.5 dolphins/h, respectively).

While it may appear to 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 (Goodall, 1994), a recent study (Heinrich, 2006) showed that local populations may be very small; at southern Chiloé, the size of the local population amounted to only 59.

Finally, a boat survey conducted between the southern tip of Chiloe and Ushuaia made only few sightings of Chilean dolphins (Dawson 2009), confirming the general decrease in abundance from north to south.

4. Biology and Behaviour

Habitat: The Chilean dolphin inhabit 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 (Goodall, 1994). In Yaldad Bay, southern Chile, shallow waters (5-10 m) near the coast and rivers were the most significant environmental features determining fine-scale dolphin distribution patterns(Ribeiro et al. 2007).Although most sightings have been near shore and therefore it is considered a coastal species, little scientific survey effort has been made in offshore waters (Goodall, 1994).

Schooling: The usual group size is from two to 10 dolphins; 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 4,000 animals, which moved north past Queule (39°22'S), hugging the shore (Goodall, 1994). The species may associate with Lagenorhynchus australis (Goodall, 1994; Jefferson et al. 1993).

Food: C. 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 (Goodall, 1994 and refs. therein).

Behaviour: Off central Chile, three behaviour categories were recorded (feeding, socialising, and travelling) in both areas (Perez-Alvarez et al. 2007). Foraging was the most frequently observed activity. Aquaculture activities in the area were observed to affect dolphin habitat use patterns by restricting space available for biologically important dolphin behaviours (Ribeiro et al. 2007).
In the southern part of the range the dolphins 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 Carwardine (1995).

5. Migration

The Chilean dolphin is thought to occur more or less continuously throughout its range, and nothing is known of its movements or migration. 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 occur throughout the year in the northern part of the range (north of Chiloé) (Perez-Alvarez et al. 2007) and during most months in the central and southern section have been reported (Goodall, 1994).

6. Threats

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 harpooned them 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 santolla) and "centolion" (false king crab, Paralomis granulosa) 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 were taken per week per boat, and that as many as 1,300-1,500 dolphins were harpooned per year in the area near the western Strait of Magellan in the early 1980s. 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, fishermen 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, 2009). 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 alone (Goodall, 1994, and refs. therein). Around Chiloe, where gillnets are employed to catch escaped salmon, bycatch may cause a significant population decline (Dawson, 2009).

Mariculture: Aquaculture farms for salmon and shellfish also may have negative effects on Chilean dolphins, e.g. by restricting their movements and eliminating important habitat along the east coast of Isla Grande de Chiloé. Finally, there is evidence that Chilean dolphins are sometimes caught incidentally in anti-sea lion nets set up around salmon farms in the fjords and channels (Reeves et al. 2008). Dolphins also react negatively to boat presence, emphasizing the need to consider boat traffic disturbance on cetaceans in coastal management plans (Ribeiro et al. 2005).

7. Remarks

Range states (Reeves et al. 2008) : Argentina, Chile

C. eutropia is included in Appendix II of the CMS: 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. The species is listed in Appendix II of CITES.

The species is listed as "Near Threatened" by the IUCN: Total population size appears to be low (in the low thousands) and decline via catches and bycatch seems to be continuing, although the decline rate is unknown. Collection of by-catch and sighting data is therefore 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 (Dawson, 2002; 2009).

In a recent CMS review (Hucke-Gaete, 2000; see Appendix 1) the main reasons for a regional conservation agreement on southern South-American small cetaceans including C. eutropia were developed.

8. Sources

· Carwardine M (1995) Whales, dolphins and porpoises. Dorling Kindersley, London, UK, 257 pp.
· Dawson SM (2009) Cephylorhynchus dolphins. In: Encyclopedia of marine mammals, 2nd Ed. (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, Amsterdam, pp. 191-196.
· 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 Press, London, pp. 269-288.
· Heinrich S (2006) Ecology of Chilean dolphins and Peales dolphins at Isla Chiloé, Southern Chile. Ph D Thesis, U. St. Andrews, UK.
· 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.
· Perez-Alvarez MJ, Alvarez E, Aguayo-Lobo A, Olavarria C (2007) Occurrence and distribution of Chilean dolphin (Cephalorhynchus eutropia) in coastal waters of central Chile. N Z J Mar Freshw Res 41: 405-409
· Reeves RR, Crespo EA, Dans Jefferson TA, Karczmarski L, Laidre K, O'Corry-Crowe G, Pedraza S, Rojas-Bracho L, Secchi ER, Slooten E, Smith BD, Wang JY, Zhou K (2008) Cephalorhynchus eutropia. In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>.
· Ribeiro S, Viddi FA, Freitas TRO (2005) Behavioural responses of Chilean dolphins (Cephalorhynchus eutropia) to boats in Yaldad Bay, Southern Chile. Aquat Mamm 31: 234-242
· Ribeiro S, Viddi FA, Cordeiro JL, Freitas TRO (2007) Fine-scale habitat selection of Chilean dolphins (Cephalorhynchus eutropia): Interactions with aquaculture activities in southern Chiloe Island, Chile. J Mar Biol Assoc UK 87: 119-128
· Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy, Spec Publ 4 , Lawrence, KS. USA.

© Boris Culik (2010) Odontocetes. The toothed whales: "Cephalorhynchus eutropia". UNEP/CMS Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.