The Spectacled porpoise (scientific name: Phocoena dioptrica) is one of six species of marine mammal in the family Phocoenidae. The other five are the Finless porpoise, the Harbour porpoise, the Gulf of California harbor porpoise, Burmeister's porpoise, and Dall's porpoise. The specicies gets its name from the fact that the eyes are surrounded by black circles that look like glasses. Spectacled porpoises are rarely seen and are found only in the oceans of the southern hemisphere. Usually they are found near the southern east coast of South America (from Uruguay and Argentina to Cape Horn) and also near the Falkland Islands and South Georgia. Spectacled porpoises have been seen near New Zealand, Macquarie Island and the Auckland Islands in the Pacific Ocean, and Heard Island and the Kerguelen Islands in the Indian Ocean.
|Phocoena dioptrica Source: Collection Georges Declercq|
|Size comparison of an average human against the Spectacled porpoise. Source: Chris Huh|
The size of this species can vary from about 1.25 meters (females) to 2.24 meters (males), evincing a fundamental sexual dimorphism. The adult body mass of A. dioptrica varies from 55 to 80 kilograms; the largest individual found was 115 kilograms.
The dorsal side is a blue-black color and the ventral side is pure white. There is a sharp line that divides the dorsal black color from the ventral white color. There is a gray line that goes from the corners of the mouth to the leading edge of the pectoral flippers, which are white. The lips are also black and the eyes are surrounded by black circles that look like glasses.
The tail fluke is dark on the top side and white on the bottom. Shape also distinguishes this species. The dorsal fin is big and triangular and the pectoral fins are small and rounded when compared to other Phocoena species.
The teeth in the upper jaw number between 18 and 23 and the teeth in the lower jaw number between 16 and 19 on each side. The teeth have spade-shaped crowns, which is a distinguishing characteristic of Phocoenidae when compared to delphinidae, which have cone-shaped crowns. There also are some skull features that distinguish the spectacled porpoise from the harbour (common) porpoise: the top of the rostrum of the spectacled porpoise is flatter, and from the side, the premaxillary bones of the spectacled porpoise are less visible. (Bannister, Kemper, and Warneke, September 1996; Brownell and November 21, 1975; Coffey, 1977; Minasian, Balcomb, and Foster, 1984; Nowak, 1999; Tinker, 1988)
Other Physical Features: Endothermic; Homoiothermic; Bilateral symmetry
Key reproductive features of the species are: Iteroparous; Gonochoric/gonochoristic/dioecious (sexes separate); Sexual; Fertilization; Viviparous; however, relatively little information is available on details of the mating systems of this species. All mammals reproduce sexually via internal fertilization and all eutherian mammals give birth to live young. However, little else is known about the reproductive behaviours of the Spectacled porpoise. One near-term fetus was recorded in July 1912 and another was taken in August of the same year. The first fetus was a female and was 484 millimetres long. No information was recorded on the second fetus. The young are most likely born in early spring, but no information is recorded. (Brownell and November 21, 1975; Minasian, Balcomb, and Foster, 1984; Tinker, 1988)
A feature common to all eutherian mammals is that females nuture their young inside their bodies until birth, and afterwards provide them with milk. However, no specific information on parental investment is available for A. dioptrica.
Key species behaviours are: natatorial; motile; solitary; and social. This species does not travel in large groups. They are likely solitary animals, but they have been seen in small aggregations of two or three individuals. They are probably not migratory. (Bannister, Kemper, and Warneke, September 1996; Tinker, 1988)
Voice and Sound Production
Little has been recorded regarding acoustical communication or perception of A. dioptrica, but the species probably uses echolocation in the same manner as other porpoises.
Distribution and Movements
The IUCN Red List notes that the Spectacled porpoise was previously known "primarily from the southern coast of eastern South America, from Uruguay and southern Brazil to Tierra del Fuego, this species is now known from offshore in the southern Hemisphere (Brownell and Clapham 1999). There are records from the Falkland Islands, South Georgia, Kerguelen Islands, Heard Island, Macquarie Island, and the Auckland Islands. Although rarely seen at sea (there are only a few dozen live sightings), this information suggests that the spectacled porpoise’s range may be circumpolar in the sub-Antarctic zone (with water temperatures of at least 1-10°C) (Goodall 2002). The southernmost sighting is from 64°34'S."
Spectacled porpoises prefer cold ocean waters of the southern hemisphere. They normally live near offshore islands but are sometimes found in the open ocean. In any case they may be considered a temperate and subantarctic marine species. They seem to prefer the subantarctic area where there are cold currents like the Falkland Current. (Bannister, Kemper, and Warneke, September 1996; Nowak, 1999)
The food preferences of spectacled porpoises are not well known. They are most likely similar to other porpoises, which eat bony fishes such as actinopterygii, Cephalopoda, mollusks and crustacea. (Bannister, Kemper, and Warneke, September 1996)
Porpoises are predators of fish and aquatic invertebrates, and they sometimes provide a food source to Killer whales. Nothing specific is known about the role of A. dioptrica in the ecosystem.
Little has been recorded about predation of A. dioptrica. It is possible that Orcinus orca are their only natural predators. This porpoise species is are hunted by humans. (Bannister, Kemper, and Warneke, September 1996; Brownell and November 21, 1975; Coffey, 1977)
Economic Importance for Humans
Spectacled porpoises have no recorded adverse affects on humans. (Tinker, 1988) Native peoples in South America hunt A. dioptrica, but not for commercial uses. (Coffey, 1977)
Threats and Conservation Status
According to the IUCN Red List reports, Spectacled porpoises are often be taken deliberately for crab bait off southern Chile. The effects of these catches on Spectacled porpoise subpopulations are not known (Jefferson et al.1993). Like all phocoenoids, Spectacled porpoises are frequently captured in gillnets as bycatch. At least 34 animals were killed incidentally between 1975 and 1990 in coastal gill-nets set in Tierra del Fuego, and there was a co-occurrence of strandings and fishing activity in southeastern Chile, suggesting additional undocumented mortality from this source. Some mortality of Spectacled porpoises was also reported from bottom and mid-water trawls off the coast of Chubut, Argentina (Brownell and Clapham, 1999).
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