Burmeister's Porpoise (버마이스터돌고래)

 

버마이스터돌고래(Phocoena spinipinnis)

영명 : Burmeister's Porpoise

 

몸길이 : 1.8m. 등지느러미가 돌고래중에서 가장 뒤쪽에 자리하고 있다. 남아메리카 온대에서 아한대에 서식하고 있다.

 

◈ 500 마리 이하.

 

 

 

Description

The body is robust with a small, blunt head and relatively large flippers. The dorsal fin is triangular in shape and canted backward in a unusual fashion for a cetacean. The Spanish name for this porpoise "marsopa espinosa" meaning "spiny porpoise" refers to the series of tubercles present in the dorsal fin. Coloration varies from dark to brownish grey on the back and sides, and a light grey on the ventral region. A dark patch often surrounds the eye. A dark grey stripe runs from the chin to the base of the flipper. A pair of stripes is also present on the abdominal region.

Distribution

Phocoena spinipinnis ranges on the west coast of South America from Paita (05°11'S), Peru, south to Valdivia (39°46'S), Chile; on the east coast of South America from Santa Catarina (28°48'S), Brazil, south to Chubut (42°25'S), Argentina ; and in coastal waters around Tierra del Fuego.

Burmeister's Porpoise may be one of the most abundant small cetaceans living around the coasts of southern South America, but it is shy and easy to overlook, and so it is poorly known. Whether Burmeister's porpoise has a continuous distribution throughout its range is unclear. There are numerous gaps in the known distribution along both Atlantic and Pacific coasts, but it is likely that many or most of these simply reflect a lack of survey effort in the areas concerned.

 

Population size

There are no quantitative data on abundance. Burmeister's porpoise is very difficult to detect in any but calm conditions, a fact that may explain the discrepancy between the assumed abundance of this animal in coastal waters on the one hand and the relative rarity of field observations on the other. The animal's respiratory and diving behaviour does not lend itself to easy observation: swimming is highly unobtrusive, surfacing is quiescent, and relatively prolonged dives of 1~3 mm are common.

 

Habitat

This is essentially a coastal species, which sometimes frequents rivers and estuaries and, off Tierra del Fuego, is occasionally observed inside the kelp line. Its habitat preferences seem to closely resemble those of the harbour porpoise, which is typically found shoreward of the 60 m isobath, but occasionally they have been recorded offshore in up to 1000m of water. However, there have also been records from more offshore waters, 50 km from the coast of Argentina.
Burmeister's porpoise is found associated with a broad range of water temperatures. At the southern limit of its distribution near Cape Horn and Tierra del Fuego, water temperatures range from 3°C in June to about 9°C in the summer months. To the north, the species appears to be associated with temperate waters in the two major northward flowing currents of South America, the Humboldt and Falklands currents. The highest recorded temperature associated with a Burmeister's sighting was 19.5°C in Golfo San José, Argentina.

 

Behaviour

A limited number of observations indicate that it is a very shy animal. Some records suggest that small groups scatter when frightened, or approached by a boat, and regroup later. It is believed to move very close to shore after dark.

Schooling: Very little is known about the natural history of this species. Most sightings are of less than 6 individuals, but aggregations of up to 70 have been reported. Behaviour of this species is inconspicuous ; they breathe with little surface disturbance.

Food: Feeding is on demersal and pelagic fish, such as anchovies (Engraulis spp.) and hake (Merluccius gayi), as well as squid, and the stomachs of some Chilean animals also contained small snails, crustaceans and mollusc egg capsules. Further prey species are sardines, jack mackerel and drums.

 

Reproduction

There appears to be a protracted summer birth peak; most births in Peru apparently occur in late summer to autumn.

Migration

A year-round population of Burmeister's porpoise appears to exist in the Beagle Channel, suggesting site-fidelity; sightings have been made in every month except August and September. Data on seasonal movements are sparse and come largely from entanglements and incidental sightings. At Golfo San José, Argentina, Phocoena spinipinnis is observed almost exclusively in spring and summer. This suggests that seasonal movement (either north-south or inshore-offshore) does occur, although whether this is correlated with water temperature or abundance of prey is unknown. Seasonal porpoise movements inferred from capture rates of the "corvina" fishery off Valdivia, Chile, with animals caught inshore (up to 18.5km from the coast) in summer, and offshore (18~37km) in winter, are biased by fishing methods : fishermen move their nets offshore in winter. Although it is unclear whether this by-catch truly reflects movements by the porpoises, it is possible that Burmeister's porpoises migrate offshore to match seasonal movements of potential prey, sardines.

Threats

◈ Direct catch

 It is widely suspected that Burmeister's porpoises are shot or harpooned for use as crab bait in southern Chile. However, because quantitative data are lacking, the extent of this problem is unknown. The most extensive known takes occur in Peruvian waters, where Burmeister's porpoise is caught primarily in net fisheries, and where it has been used extensively for human consumption. Mortality in Peru was recently estimated as > 450 per year and the high mortality is cause for considerable concern. Reyes states that annual captures in Peru may reach as high as 2000 animals (see also mundo azul in "links").

 

◈ Incidental catch

By-catch occurs in various areas within the species' range, including Peru, Chile, Argentina, Uruguay and Brazil. Coastal or shark gill net fisheries are also responsible for mortality in Burmeister's porpoise in Argentina (> 12 per year), Tierra del Fuego, and, to a lesser extent, Uruguay. Takes are poorly documented in all areas.

 

Status : CITES - Appendix I. IUCN ; Endangered