The spectacled porpoise (''Phocoena dioptrica'') is a small to midsize

porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...

indigenous to the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

. 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.

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. 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 . The spectacled porpoise has a distinctive colouration. As an adult it is

countershaded Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...

, with a black dorsal region which is sharply delineated from a white belly. In some individuals, this line can be feathered. 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. Females are described as lighter in colouration, 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 range/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 0.9 °C and 10.3 °C. Stranded individuals have been found across the southern hemisphere. In the south-western Atlantic records have been made at Santa Catarina in Southern Brazil,

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

, from

Buenos Aires Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata, on South ...

Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla G ...

, and the

Falkland Islands The Falkland Islands (; es, Islas Malvinas, link=no ) is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and about from Cape Dubouzet ...

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 New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, Burney Island,

Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...

and South Australia. This widespread distribution is evidence of a circumpolar range, and possible association with the

Falkland Current The Falkland Current (also called Malvinas Current or Falklands Current) is a cold water current that flows northward along the Atlantic coast of Patagonia as far north as the mouth of the Río de la Plata. This current results from the movement o ...

and

Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feat ...

(ACC) which transports cold water along the Atlantic coast of South America, and around Antarctica respectively. Sightings of spectacled porpoise at sea are similarly widespread, and include waters off

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

, South Georgia, Kerguelen, south of New Zealand, Tasmania and Heard Island. Nine sightings have been made south of 64°, in Antarctic waters.

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 An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 species are placed in 1 ...

(Eugraulis sp.), stomatopods,

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

beaks (Sepia sp.) and a half digested ornate cowfish (''Aracana ornata'').

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 long in late spring or summer (November to February). 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 . 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 Burmeister's porpoise (''Phocoena spinipinnis'') 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. Locally it is known as ''marsopa espinosa'' (t ...

(''Phocoena spinipinnis'') than to the

vaquita The vaquita ( ; ''Phocoena sinus'') is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Averaging (females) or (males) in length, it is the smallest of all living cetaceans. The species i ...

(''Phocoena sinus'') which appeared to diverge from Burmeister’s and spectacled porpoises in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 These three species diverged from the

harbour porpoise The harbour porpoise (''Phocoena phocoena'') 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 ...

(''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.

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. 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 Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...

, leopard seals (''Hydrurga leptonyx'') and

killer whales The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white pat ...

(''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. 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. Bycatch and incidental capture are most likely the greatest anthropogenic threat to the spectacled porpoise. 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. The extent of incidental bycatch is unknown, however strandings and fishing ground locations often coincide.

Conservation status

While previously listed by the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

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.

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. 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.

References

External links

Whale & Dolphin Conservation (WDC)
{{DEFAULTSORT:Spectacled Porpoise Porpoises Mammals of Argentina Mammals of Chile Fauna of the Auckland Islands Mammals described in 1912