Spectacled porpoise
Spectacled porpoise | |
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Subadult female spectacled porpoise | |
Size compared to an average human | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Infraorder: | Cetacea |
Family: | Phocoenidae |
Genus: | Phocoena |
Species: | P. dioptrica
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Binomial name | |
Phocoena dioptrica Lahille, 1912
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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]
Description
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. Interestingly, this porpoise species shows obvious sexual dimorphism between adult males and females, as the dorsal fins in the former are much larger and more rounded.[4]
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).[4]
The spectacled porpoise has a distinctive colouration. As an adult it is
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.[6] 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).[4]
Stranded individuals have been found across the southern hemisphere. In the south-western Atlantic records have been made at Santa Catarina in Southern Brazil,
Sightings of spectacled porpoise at sea are similarly widespread, and include waters off
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
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).[9] No information is available on gestation, lactation, or inter-birth intervals.
Taxonomy
The species was named by the French naturalist Fernando Lihille 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 .[10] 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.[11]
Phylogenetic tree analyses found that spectacled porpoises are more closely related to
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
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.[15] 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.[6]
Bycatch and incidental capture are most likely the greatest anthropogenic threat to the spectacled porpoise.[16] 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.[6] The extent of incidental bycatch is unknown, however strandings and fishing ground locations often coincide.[9]
Conservation status
While previously listed by the
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.[5] 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.[17]
See also
References
- . Retrieved 18 November 2021.
- ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
- ^ S2CID 257454374.
- ^ ISBN 978-0-12-804327-1.
- ^ .
- ^ a b c Jefferson, T.A.; Curry, B.E. (1993). "A global review of porpoise (Cetacea: Phocoenidae) mortality in gillnets". Biological Conservation. 67 (2): 197–183.
- ^ a b Pinedo, M.C.; Barreto, A.S.; Lammardo, M.P.; Andrade, A.L.V.; Geracitano, L (2002). "Northernmost records of the spectacled porpoise, Layard's beaked whale, Commerson's dolphin, and Peale's dolphin in the southwestern Atlantic Ocean". Aquatic Mammals. 28: 32–37.
- ^ "Little known about rare porpoise". 18 September 2014.
- ^ a b Goodall, R.N.P.; Schiavini, A.C.M. (1995). "On the biology of the spectacled porpoise, Australophocoaena dioptrica". Report of the International Whaling Commission.
- ISBN 978-0-375-41141-0.
- hdl:11336/68238.
- PMID 8747302.
- ^ )
- ISBN 978-0-12-804327-1.
- ^ Piana, W.F.; Goodall, R.N.P.; Galeazzi, A.R.; Sobral, A.P. (1985). "Cetacean remains in Beagle Channel shell middens". Sixth Biennial Conference on the Biology of Marine Mammals.
- ^ a b Dellabianca, N.; Pitman, R.L.; G., Braulik (2018). Phocoena dioptrica, Spectacled Porpoise (Report). The IUCN Red List of Threatened Species 2018: e.T41715A50381544.
- ^ "Spectacled Porpoise Rescued in Argentina". 14 February 2019. Retrieved 10 October 2020.