Spectacled porpoise

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Spectacled porpoise
Subadult female spectacled porpoise.png
Subadult female spectacled porpoise
Spectacled porpoise size.svg
Size compared to an average human
CITES Appendix II (CITES) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Phocoenidae
Genus: Phocoena
Species:
P. dioptrica
Binomial name
Phocoena dioptrica
Lahille, 1912
Cetacea range map Spectacled Porpoise.PNG
Spectacled porpoise range
Synonyms

Australophocaena dioptrica

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. [3]

Contents

The species was first described in 1912 by Fernando Lahille. [4] [5]

Description

Stranded male spectacled porpoise nearby Dunedin in New Zealand Stranded male spectacled porpoise.jpg
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. [6]

Records for female length range up to 204 centimetres (80 in), while males may reach 224 centimetres (88 in), which represents the largest specimen documented thus far. The maximum weight for a female was 85 kilograms (187 lb), while a male has been recorded at 110 kilograms (240 lb). [6]

The spectacled porpoise has a distinctive coloration. As an adult it is countershaded, with a black dorsal region which is sharply delineated from a white belly. In some individuals, this line can be feathered. [6] An obvious dark eye patch is present in both juveniles and adults. A pale ‘saddle-patch’ around the dorsal fin and a dark line around the blowhole have also been documented. [7] 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. [8] 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 0.9 and 10.3 °C (33.6 and 50.5 °F). [6]

Stranded individuals have been found across the southern hemisphere. In the south-western Atlantic records have been made at Santa Catarina in Southern Brazil, [9] 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, [10] 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. [6]

Sightings of spectacled porpoise at sea are similarly widespread, and include waters off Patagonia, South Georgia, Kerguelen, south of New Zealand, Tasmania and Heard Island. Nine sightings have been made south of 64°, in Antarctic waters. [3]

Foraging

Little dietary information is available for the spectacled porpoise, but it is thought to forage on fish and squid. No observations of foraging behaviour at sea have been made. Stomach contents from a small number of stranded specimens included anchovy ( Engraulis sp.), stomatopods, cephalopod beaks ( Sepia sp.) and a half digested ornate cowfish ( Aracana ornata ). [3] [9]

Reproduction

Little is known about the reproduction of the spectacled porpoise. In the Tierra del Fuego region, studies estimate that young porpoises are born at 100 centimetres (39 in) long in late spring or summer (November to February). [11] 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. [12] 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. [13]

Phylogenetic tree analyses found that spectacled porpoises are more closely related to Burmeister's porpoise (Phocoena spinipinnis) [14] than to the vaquita (Phocoena sinus) which appeared to diverge from Burmeister’s and spectacled porpoises in the Pliocene era. [15] 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. [15]

Population status

The population size and its inter-connectedness across the Southern Ocean is unknown. Research cruises conducted between 1978 and 2004 in the Antarctic resulted in 28 sightings, however these were made in fair weather conditions and porpoises may have been missed during poorer conditions. [3] It is possible that Passive Acoustic Monitoring (PAM) for spectacled porpoises may shed more light on their range and habitat use, however no studies have been conducted to date.

Threats

The spectacled porpoise is likely prey for sharks, leopard seals (Hydrurga leptonyx) and killer whales (Orcinus orca). In Tierra del Fuego, it has been observed that scavenging birds such as kelp gulls will target stranded spectacled porpoise carcasses over other cetacean species. Such scavenging can result in a carcass becoming skeletonised rapidly, within one to two hours. [16]

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. [17] 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. [8]

Bycatch and incidental capture are most likely the greatest anthropogenic threat to the spectacled porpoise. [1] Porpoises and other small cetaceans are particularly at risk of entanglement and drowning in gillnets, as the thin filaments are not easily detected by their echolocation clicks. [8] The extent of incidental bycatch is unknown, however strandings and fishing ground locations often coincide. [11]

Conservation status

While previously listed by the IUCN in 2008 as ‘Data Deficient’ the species was upgraded to ‘Least Concern’ in 2018. While it is widely accepted that spectacled porpoises are threatened by fishery bycatch and entanglement, and stranding rates in Tierra del Fuego may be unsustainable for the population, the category of Least Concern has been applied provisionally until more data is available. [1]

Captivity

At least two incidents have been documented where a living spectacled porpoise was taken into captivity, in both cases for medical treatment and rehabilitation following stranding. The first individual was a very young 127 cm long female calf that stranded in Port Elliot, Southern Australia, on 24 March 1997. [7] The calf was disorientated and exhausted, preventing refloating attempts, and rescuers subsequently transported the calf to the Royal Society for the Prevention of Cruelty to Animals (RSPCA) marine rescue unit in Adelaide. The porpoise died five days later on 29 March 1997, and a necropsy revealed damage to the oesophagus and first stomach caused by intubation during force-feeding. However, other organs were normal and no direct cause of death was determined.

The second incident occurred on 26 January 2019, where an adult male live stranded 30 km up a river estuary in Argentina. The porpoise was emaciated and dehydrated, and was taken to the Marine Fauna Rescue and Rehabilitation Centre. The animal died four days later on 30 January 2019. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Porpoise</span> Small cetacean of the family Phocoenidae

Porpoises are small dolphin-like cetaceans classified under the family Phocoenidae. Although similar in appearance to dolphins, they are more closely related to narwhals and belugas than to the true dolphins. There are eight extant species of porpoise, all among the smallest of the toothed whales. Porpoises are distinguished from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak, although some dolphins also lack a pronounced beak. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates.

<span class="mw-page-title-main">Hector's beaked whale</span> Species of mammal

Hector's beaked whale, is a small mesoplodont living in the Southern Hemisphere. This whale is named after Sir James Hector, a founder of the colonial museum in Wellington, New Zealand. The species has rarely been seen in the wild.

<span class="mw-page-title-main">Strap-toothed whale</span> Species of whale

The strap-toothed beaked whale, also known as Layard's beaked whale, is one of the largest members of the Mesoplodon genus, growing to 6.2 m (20 ft) in length and reaching up to 1,300 kg (2,900 lb). The common and scientific name was given in honor of Edgar Leopold Layard, the curator of the South African Museum, who prepared drawings of a skull and sent them to the British taxonomist John Edward Gray, who described the species in 1865.

<span class="mw-page-title-main">Harbour porpoise</span> Species of mammal

The harbour porpoise is one of eight extant species of porpoise. It is one of the smallest species of cetacean. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar porpoise to whale watchers. This porpoise often ventures up rivers, and has been seen hundreds of kilometres from the sea. The harbour porpoise may be polytypic, with geographically distinct populations representing distinct races: P. p. phocoena in the North Atlantic and West Africa, P. p. relicta in the Black Sea and Sea of Azov, an unnamed population in the northwestern Pacific and P. p. vomerina in the northeastern Pacific.

<span class="mw-page-title-main">Vaquita</span> Species of porpoise

The vaquita is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Reaching a maximum body length of 150 cm (4.9 ft) (females) or 140 cm (4.6 ft) (males), it is the smallest of all living cetaceans.

<span class="mw-page-title-main">Burmeister's porpoise</span> Species of marine mammal

Burmeister's porpoise is a species of porpoise endemic to the coast of South America. It was first described by Hermann Burmeister, for whom the species is named, in 1865.

<span class="mw-page-title-main">Shepherd's beaked whale</span> Species of mammal

Shepherd's beaked whale, also commonly called Tasman's beaked whale or simply the Tasman whale, is a cetacean of the family Ziphiidae and the only species in the genus Tasmacetus. The whale has not been studied extensively. Only four confirmed at sea sightings have been made and 42 strandings recorded. It was first known to science in 1937, being named by W. R. B. Oliver after George Shepherd, curator of the Wanganui Museum, who collected the type specimen near Ohawe on the south Taranaki coast of New Zealand's North Island, in 1933.

<span class="mw-page-title-main">Commerson's dolphin</span> Species of mammal

Commerson's dolphin, also referred to by the common names jacobita, skunk dolphin, piebald dolphin, panda dolphin, or tonina overa, is a small oceanic dolphin of the genus Cephalorhynchus. Commerson's dolphin has two geographically-isolated but locally-common subspecies. The principal subspecies, C.c.commersonii, has sharply-delineated black-and-white patterning and is found around the tip of South America. The secondary subspecies, C.c.kerguelenensis, is larger than C.c.commersonii, has a less-sharply delineated dark and light grey patterning with a white ventral band, and is found around the Kerguelen Islands in the Indian Ocean.

<span class="mw-page-title-main">Pygmy killer whale</span> Species of mammal

The pygmy killer whale is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus Feresa. It derives its common name from sharing some physical characteristics with the orca, also known as the killer whale. It is the smallest cetacean species that has the word "whale" in its common name. Although the species has been known to be extremely aggressive in captivity, this aggressive behavior has not been observed in the wild.

<span class="mw-page-title-main">Melon-headed whale</span> Species of mammal

The melon-headed whale, also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from the head shape. Melon-headed whales are widely distributed throughout deep tropical and subtropical waters worldwide, but they are rarely encountered at sea. They are found near shore mostly around oceanic islands, such as Hawaii, French Polynesia, and the Philippines.

<span class="mw-page-title-main">Southern right whale dolphin</span> Species of mammal

The southern right whale dolphin is a small and slender species of cetacean, found in cool waters of the Southern Hemisphere. It is one of two species of right whale dolphin. This genus is characterized by the lack of a dorsal fin. The other species, the northern right whale dolphin, is found in deep oceans of the Northern Hemisphere and has a different pigmentation pattern than the southern right whale dolphin.

<span class="mw-page-title-main">Hourglass dolphin</span> Species of mammal

The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. It is commonly seen from ships crossing the Drake Passage but has a circumpolar distribution.

<span class="mw-page-title-main">Cetacean bycatch</span> Accidental capture of porpoises, whales and dolphins

Cetacean bycatch is the accidental capture of non-target cetaceans such as dolphins, porpoises, and whales by commercial fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets.

Rae Natalie Prosser de Goodall April 13, 1935, near Lexington, Ohio, United States – May 25, 2015, Estancia Harberton, Tierra del Fuego Province, Argentina,) also known as Natalie Goodall, was a botanist, cetologist, illustrator, natural historian and local historian based in Tierra del Fuego Province, Argentina and known for studying the region's flora and fauna.

References

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