The spectacled porpoise (Phocoena dioptrica) is a small to midsize porpoise indigenous to the Southern Ocean. It is one of the most poorly studied cetaceans, partly due to its remote range in the Southern Ocean. What little is known about this porpoise species has been gathered mainly from stranded individuals, and a few observations of living animals made at sea.

The species was first described in 1912 by Fernando Lahille.

Description

thumb|left|Stranded male spectacled porpoise nearby [[Dunedin in New Zealand]]

As with other porpoise species, the spectacled porpoise has no beak. It has small pectoral fins with rounded tips positioned far forward on the body, and a triangular dorsal fin. This porpoise species shows obvious sexual dimorphism between adult males and females, as the dorsal fins in males are much larger and more rounded than those of females.

Records for female length range up to , while males may reach , which represents the largest specimen documented thus far. The maximum weight for a female was , while a male has been recorded at . Females are described as lighter in coloration, while young animals may have a dorsal area that is grey rather than black, with a lighter grey on the belly, a clearly demarked line connecting the mouth and flipper.

Geographic distribution

The distribution of the spectacled porpoise is thought to be circumpolar, and it is considered a predominately oceanic species, however occasional sightings and specimens are documented in coastal regions. Evidence from sightings and strandings suggest that the species can be found within cool temperate, sub-Antarctic and Antarctic waters, where water temperatures range between . Uruguay, from Buenos Aires to Tierra del Fuego, and the Falkland Islands and South Georgia. Records exist from the south-western South Pacific (Auckland and Maquarie Islands) to the southern Indian Ocean (Heard and Kerguelen), and also from New Zealand, Burney Island, Tasmania and South Australia. This widespread distribution is evidence of a circumpolar range, and possible association with the Falkland Current and Antarctic Circumpolar Current (ACC) which transports cold water along the Atlantic coast of South America, and around Antarctica respectively. No information is available on gestation, lactation, or inter-birth intervals.

Taxonomy

The species was named by the French-born Argentinian zoologist Fernando Lahille in 1912 for its two distinctive black eye patches, with the latin dioptrica meaning 'spectacled'. In Spanish, the spectacled porpoise is known as 'marsopa de anteojos', a literal translation of the English common name. Recent analyses of mitochondrial DNA from 50 porpoises indicated high levels of genetic diversity that would indicate a large and stable population, or one with a wide distribution. The study also revealed evidence for a recent expansion in population.

Phylogenetic tree analyses found that spectacled porpoises are more closely related to Burmeister's porpoise (Phocoena spinipinnis) than to the vaquita (Phocoena sinus) which appeared to diverge from Burmeister's and spectacled porpoises in the Pliocene era. These three species diverged from the harbour porpoise (Phocoena phocoena) and Dall's porpoise ( Phocoenoides dalli) around 4 million years ago, while the split between Burmeister's and spectacled porpoises occurred 2.3 million years ago.

Researchers have uncovered spectacled porpoise remains within the kitchen middens of the canoe people who lived in Tierra del Fuego between 6000 and 1400 years ago. It is possible the species was once a common food source for peoples in the region. More recently, porpoises may be caught and used as bait for the crab fishery industry, however the frequency of this activity and its impact on porpoise population status is unknown.

See also

  • List of cetaceans
  • Marine biology

References

  • Whale & Dolphin Conservation (WDC)
  • Convention on Migratory Species page on the Spectacled porpoise