Octopus tetricus

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Octopus tetricus
Octopus tetricus 118664956.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Family: Octopodidae
Genus: Octopus
Species:
O. tetricus
Binomial name
Octopus tetricus
Gould, 1852 [1]
Synonyms [2]

Octopus gibbsiO'Shea, 1999

Octopus tetricus, the gloomy octopus or the common Sydney octopus, [3] is a species of octopus from the subtropical waters of eastern Australia and New Zealand. [2] O.tetricus belongs to the Octopus vulgaris species group and is a commercially prized species. All species within the O. vulgaris group are similar in morphology. [4] The English translation of O. tetricus (Latin) is 'the gloomy octopus'. [5]

Contents

Distribution

Octopus tetricus was originally discovered in New South Wales and was also found along the eastern Australian coastline. It occurs from Lakes Entrance in Victoria [5] to Moreton Bay in southern Queensland. [6] Octopus tetricus is distributed in the subtropical seas of eastern Australia and northern New Zealand, including Lord Howe Island. A close relative, Octopus djinda , occurs at similar latitudes in Western Australia, from Shark Bay to Cape Le Grand, [5] and was considered to be conspecific with O. tetricus until 2021. It is one of the most common species of octopus found in New Zealand, alongside Pinnoctopus cordiformis and Macroctopus maorum . [7]

Anatomy and morphology

A gloomy octopus under a rock in Clovelly Pool, Sydney Gloomy Octopus-Octopus tetricus.JPG
A gloomy octopus under a rock in Clovelly Pool, Sydney
Octopus tetricus observed north of Auckland, New Zealand. Octopus tetricus New Zealand 181759846.jpg
Octopus tetricus observed north of Auckland, New Zealand.

Octopus tetricus is normally coloured grey to mottled brown with rufous arm faces that taper towards the tip. Their eyes are typically white in colour. The skin has many small irregularly shaped patches and large warty structures used to make it appear spiky when the octopus camouflages itself as seaweed. [3] The adults typically have a tentacle span of 2 metres (6.6 ft). [8]

Taxonomy and etymology

Octopus tetricus Gould, 1852 was described by American conchologist Augustus Addison Gould in the 1852 publication, Mollusca of the United States Exploring Expedition under Captain Charles Wilkes. [9] An illustration of O. tetricus was also published a few years later (plate 47). [10]

The type specimen is listed as being from Sydney, New South Wales, Australia. [9] The type was one of many thousands of specimens collected by the Wilkes Expedition, however this particular specimen of O. tetricus is thought to be lost. [11] [12]

The New Zealand species O. gibbsii is considered to be a synonym of O. tetricus. [13]

Gloomy octopus in a rock pool north of Auckland, New Zealand. Octopus tetricus New Zealand 249300376.jpg
Gloomy octopus in a rock pool north of Auckland, New Zealand.
Octopus tetricus in a rock pool in Northland, New Zealand. Octopus tetricus New Zealand 346252155.jpg
Octopus tetricus in a rock pool in Northland, New Zealand.

The species epiethet tetricus means 'forbidding' or 'gloomy'. [5]

Life cycle

Reproduction and growth

The reproductive cycle of females is tied to seasonal changes, similar to many other species. Females reach maturity around Australia's spring and summer seasons in order to mate and lay eggs. [14] During the mating process the male O. tetricus passes spermatophores to the female in two different ways. The male either wraps his arms and web around the female's mantle or reaches his mating arm from a distance and inserts it into the female's mantle. Spermatophores are released from the male's "terminal organ", moved by the male's oral suckers, and then the spermatophores are inserted into the female's oviduct. [15]

Octopus tetricus start out as eggs that are laid in large numbers in the octopus's nest. The eggs are normally glued to the rock or substrate at the top of the den created by the female octopus. The female usually lays her eggs over several nights in a string formation. The size and number of strings of eggs usually depends on how large the female is and can have between 60 and 200 egg strings. The female then guards the eggs until they hatch. [16] Female O. tetricus have also been known to store viable spermatozoa for up to 114 days. The amount of time embryonic development takes varies with water temperature, and newly hatched O. tetricus larvae are about 2.5 mm long and 1.1mm wide. [17] These larvae go through a stage called the paralarval stage where they are considered planktonic, or free floating, organisms before they settle to the bottom and grow large enough to hunt for their food. This stage may last around 35–60 days. [18] The females of O. tetricus have been known to cannibalise the males following mating. [3]

Temperature plays a key role in growth of this octopus species. With a good food supply, octopuses that reside in areas with a cooler water temperature tend to grow slower during the key growth phase and when they reach maturity they are generally larger than octopuses that are found in warmer water temperatures. [18]

Lifespan

Adult O. tetricus is observed to have a relatively small body size and a lifespan of approximately 11 months. [14] Female O. tetricus rarely eat or sleep during the protection of the nest and die shortly after the eggs hatch. [16] Females are found to mature at a slower rate and become larger than male O. tetricus. [14]

Habitat and behavioural ecology

Habitat

Octopus tetricus occurs in the intertidal zone along rocky shores and in the ocean and it has been suggested that this species is associated more commonly with rocky reefs during the breeding season, although they frequent areas of the sea bed with soft-sediments for much of their life. [3] O. tetricus alter their habitats by digging out dens and using remains from prey, including but not limited to shells. It is very common for scallop beds to be found in close proximity to the excavated dens. The scallops serve as a food source and their shells are part of the shell beds built. This species of octopus is considered to be an ecosystem engineer. This means that the way they create their habitats influences and builds an ecosystem around their dwellings. The shell beds that are created around the excavated dens attract hermit crabs and fish due to the various hiding places created. Small fish and other small prey species attract larger species and the cycle builds, creating an ecosystem. [19] A solid object can serve as a good den that can also be the start of a new settlement for O. tetricus. [20] Studies show that O. tetricus has higher populations in patch reef habitats than broken reef habitats, and were scarcely found on flat reefs. Adult O. tetricus were also found to occupy coastal reefs in the summer and then disappear around the second week of April, which is the second week of autumn in Australia. [21] Shelters serve a vital role in octopus ecology. The species is generally known to be solitary, but complex social behaviours have been observed by scientists. [22]

Social behaviour and mating

Scientists have observed many different behaviours exhibited by O. tetricus including, signalling, mating, mate defence, and aggression. Some have even observed an octopus evicting another from its den. Occasionally this aggressive behaviour led to physical altercations between octopuses. [22] It is a territorial species which sits out the day in a lair among rocks and rubble, the rubble being collected to create a defensible lair. The lairs of this species can be identified by the shells of the octopus's prey which it scatters around its home. They move about the rocks by crawling using their arms but they can use their siphon to propel themselves through the water by generating a jet of water or to move (throw) shells, silt, and algae. [3] [23]

Observation of mating behaviours has revealed that O. tetricus females have a stronger precopulatory preference for males that have longer mating appendages, or ligulae. Both female and male octopuses mate multiple times throughout a mating season. Female octopuses are able to accept multiple spermatophores from males but they only produce one brood of eggs at the end of a mating season. [24] [ better source needed ]

Feeding and hunting

Octopus tetricus is primarily a nocturnal feeder which uses its sharp beak to feed on crustaceans and molluscs, for example sea snails and bivalves. It has also been recorded as being cannibalistic. [3]

Two areas in Jervis Bay where they congregate have been dubbed Octopolis and Octlantis, [20] [22] containing a large area of discarded shells where ten or more octopuses den and mate. [25] [26]

Fisheries

Octopus tetricus may be caught as bycatch in trawl and lobster-pot fisheries and is then sold for both human consumption and for use as bait. [3]

Conservation status

Octopus tetricus is listed as 'Least Concern' on The IUCN Red List of Threatened Species. [27]

Related Research Articles

<span class="mw-page-title-main">Octopus</span> Soft-bodied eight-limbed order of molluscs

An octopus is a soft-bodied, eight-limbed mollusc of the order Octopoda. The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beaked mouth at the center point of the eight limbs. The soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among the most intelligent and behaviourally diverse of all invertebrates.

<span class="mw-page-title-main">Squid</span> Superorder of cephalopod molluscs

A squid is a mollusc with an elongated soft body, large eyes, eight arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida. Though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.

<span class="mw-page-title-main">Cephalopod</span> Class of mollusks

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

<span class="mw-page-title-main">Blue-ringed octopus</span> Four species of mollusk

Blue-ringed octopuses, comprising the genus Hapalochlaena, are four extremely venomous species of octopus that are found in tide pools and coral reefs in the Pacific and Indian oceans, from Japan to Australia. They can be identified by their yellowish skin and characteristic blue and black rings that can change color dramatically when the animal is threatened. They eat small crustaceans, including crabs, hermit crabs, shrimp, and other small sea animals.

<span class="mw-page-title-main">Southern blue-ringed octopus</span> Species of mollusc

The southern blue-ringed octopus is one of three highly venomous species of blue-ringed octopuses. It is most commonly found in tidal rock pools along the south coast of Australia. As an adult, it can grow up to 20 centimetres (8 in) long and on average weighs 26 grams (0.9 oz). They are normally a docile species, but they are highly venomous, possessing venom capable of killing humans. Their blue rings appear with greater intensity when they become aggravated or threatened.

<i>Octopus</i> (genus) Genus of cephalopods

Octopus is the largest genus of octopuses, comprising more than 100 species. These species are widespread throughout the world's oceans. Many species formerly placed in the genus Octopus are now assigned to other genera within the family. The octopus has 8 arms, averaging 20 cm (8 in) long for an adult.

<span class="mw-page-title-main">Giant Pacific octopus</span> Species of cephalopod

The giant Pacific octopus, also known as the North Pacific giant octopus, is a large marine cephalopod belonging to the genus Enteroctopus and Enteroctopodidae family. Its spatial distribution encompasses much of the coastal North Pacific, from the Mexican state of Baja California, north along the United States' West Coast, and British Columbia, Canada; across the northern Pacific to the Russian Far East, south to the East China Sea, the Yellow Sea, the Sea of Japan, Japan's Pacific east coast, and around the Korean Peninsula. It can be found from the intertidal zone down to 2,000 m (6,600 ft), and is best-adapted to colder, oxygen- and nutrient-rich waters. It is the largest octopus species on earth and can often be found in aquariums and research facilities in addition to the ocean. E. dofleini play an important role in maintaining the health and biodiversity of deep sea ecosystems, cognitive research, and the fishing industry.

<i>Nautilus</i> (genus) Genus of molluscs

Nautilus is a marine cephalopod genus in the mollusk family Nautilidae. Species in this genus differ significantly, morphologically, from the two nautilus species in the adjacent sister-taxon Allonautilus. The oldest fossils of the genus are known from the Late Eocene Hoko River Formation, in Washington State and from Late-Eocene to Early Oligocene sediments in Kazakhstan. The oldest fossils of the modern species Nautilus pompilius are from Early Pleistocene sediments off the coast of Luzon in the Philippines.

<i>Octopus cyanea</i> Species of cephalopod known as the big blue octopus

Octopus cyanea, also known as the big blue octopus or day octopus, is an octopus in the family Octopodidae. It occurs in both the Pacific and Indian Oceans, from Hawaii to the eastern coast of Africa. O. cyanea grows to 16 cm in mantle length with arms to at least 80 cm. This octopus was described initially by the British zoologist John Edward Gray in 1849; the type specimen was collected off Australia and is at the Natural History Museum in London.

<i>Macroctopus</i> Species of mollusc

Macroctopus maorum is known more commonly as the Maori octopus or the New Zealand octopus. It is found in the waters around New Zealand and southern Australia. M. maorum is one of the largest and most aggressive octopus species living in the New Zealand and Australian waters. They feed mainly on crustaceans and fish. Although they have a short life span, the females lay thousands of eggs and are very protective of them.

<i>Callistoctopus ornatus</i> Species of mollusc

Callistoctopus ornatus is a tropical species of octopus native to the Indo-Pacific region. Other common names include white-striped octopus and night octopus, in reference to its nocturnal habits. It was previously known as Polypus ornatus. C. ornatus is edible and was recorded in a Hawaiian market in 1914 by S. S. Berry.

<span class="mw-page-title-main">Bigfin reef squid</span> Species of squid

Sepioteuthis lessoniana, commonly known as the bigfin reef squid, tiger squid, glitter squid or oval squid, is a species of loliginid squid. It is one of the three currently recognized species belonging to the genus Sepioteuthis. Studies in 1993, however, have indicated that bigfin reef squids may comprise a cryptic species complex. The species is likely to include several very similar and closely related species.

<i>Abdopus aculeatus</i> Species of cephalopod

Abdopus aculeatus is a small octopus species in the order Octopoda. A. aculeatus has the common name of algae octopus due to its typical resting camouflage, which resembles a gastropod shell overgrown with algae. It is small in size with a mantle around the size of a small orange and arms 25 cm in length, and is adept at mimicking its surroundings.

<i>Pinnoctopus cordiformis</i> Species of mollusc

Pinnoctopus cordiformis is a species of octopus found around the coasts of New Zealand. It is one of the most common species of octopus in the country.

<i>Octopus bimaculatus</i> Species of octopus

Octopus bimaculatus, commonly referred to as Verrill's two-spot octopus, is a similar species to the Octopus bimaculoides, a species it is often mistaken for. The two can be distinguished by the difference in the blue and black chain-like pattern of the ocelli. O. bimaculatus hunt and feed on a diverse number of benthic organisms that also reside off the coast of Southern California. Once the octopus reaches sexual maturity, it shortly dies after mating, which is approximately 12–18 months after hatching. Embryonic development tends to be rapid due to this short lifespan of these organisms.

<i>Octopus insularis</i> Species of octopus

Octopus insularis is a species of octopus described in 2008 from individuals found off the coast of Brazil, with a potentially much larger range.

<i>Bathypolypus sponsalis</i> Species of mollusc

Bathypolypus sponsalis, commonly called the globose octopus, is a deep sea cephalopod that can be found in both the eastern Atlantic Ocean and the Mediterranean Sea. It possesses many morphological traits adapted to a deep sea environment, including large eggs, reduced gills, no ink sac, and subgelatinous tissues. A distinguishing factor are the relatively large reproductive organs. Their diet consists of predominantly crustaceans and molluscs, but they sometimes consume fish as well. Bathypolypus sponsalis usually dies quickly after reproduction and only spawns once in their lifetime. Sexually mature females have a mantle length of at least 34 mm and sexually mature males have a mantle length of about 24 mm. Juveniles are white and transition to dark brown then to dark purple once maturity is reached.

Abdopus capricornicus is a species of octopus in the family Octopodidae, and is often also referred to as Octopus capricornicus. This octopus is native to the Great Barrier Reef and is often found throughout the Indo-West Pacific Ocean. There are six other species of octopuses within the subgenus Abdopus with a large number of organisms not yet described. This octopus is notable for its unique body patterning through which it can change. The likely uses for this characteristic are camouflage or intraspecific communication. Other organisms in the Abdopus genus include A. horridus, A. abaculus, A. aculeatus, and A. tonganus. Individuals are capable of autotomy, sacrificing a writhing arm to a predator to distract it while making an escape.

<span class="mw-page-title-main">Octopolis and Octlantis</span> Settlements of gloomy octopuses in Jervis Bay, Australia

Octopolis and Octlantis are two non-human settlements occupied by gloomy octopuses in Jervis Bay, on the south coast of New South Wales. The first site, named "Octopolis" by biologists, was found in 2009. Octopolis consists of a bed of shells in an ellipse shape, 2–3 meters diameter on its longer axis, with a single piece of anthropogenic detritus, believed to be scrap metal, within the site. Octopuses build dens by burrowing into the shell bed. The shells appear to provide a much better building material for the octopuses than the fine sediment around the site. Up to 14 octopuses have been seen at Octopolis at a single time. In 2016, a second settlement was found nearby, named "Octlantis," which includes no human-made objects and can house similar numbers of octopuses. Both sites are within Booderee National Park. Some media accounts have described these sites as octopus "cities," but researchers who have worked on the sites view this as a misleading analogy.

<i>Octopus hubbsorum</i> Species of Octopus

Octopus hubbsorum, is an octopus in the family Octopodidae. It is commonly found along tropical waters along the central Pacific Coast of Mexico. Here, they are one of the most commonly caught cephalopods and are commercially extremely important for the economy.

References

  1. ↑ "ITIS standard report - Octopus tetricus (Gould, 1852)". Integrated Taxonomic Information System . Retrieved 12 October 2014.
  2. 1 2 "Octopus tetricus Gould, 1852". World Register of Marine Species. Vlaams Instituut voor de Zee. Retrieved 29 January 2017.
  3. 1 2 3 4 5 6 7 "Common Sydney Octopus – Octopus tetricus". Australian Museum. 2012. Retrieved 29 January 2018.
  4. ↑ Amor, Michael D.; Norman, Mark D.; Roura, Alvaro; Leite, Tatiana S.; Gleadall, Ian G.; Reid, Amanda; Perales-Raya, Catalina; Lu, Chung-Cheng; Silvey, Colin J.; Vidal, Erica A. G.; Hochberg, Frederick G. (2017). "Morphological assessment of the Octopus vulgaris species complex evaluated in light of molecular-based phylogenetic inferences". Zoologica Scripta. 46 (3): 275–288. doi:10.1111/zsc.12207. hdl: 11343/291747 . ISSN   1463-6409. S2CID   88706796.
  5. 1 2 3 4 Amor, Michael D.; Hart, Anthony M. (2021-11-03). "Octopus djinda (Cephalopoda: Octopodidae): a new member of the Octopus vulgaris group from southwest Australia". Zootaxa. 5061 (1): 145–156. doi:10.11646/zootaxa.5061.1.7. ISSN   1175-5334. PMID   34810636. S2CID   243468570.
  6. ↑ Amor MD; Norman MD; Cameron HE; Strugnell JM (2014-06-25). "Allopatric speciation within a cryptic species complex of Australasian octopuses". PLOS ONE. 9 (6): e98982. Bibcode:2014PLoSO...998982A. doi: 10.1371/journal.pone.0098982 . PMC   4070898 . PMID   24964133.
  7. ↑ Vennell, Robert (5 October 2022). Secrets of the Sea: The Story of New Zealand's Native Sea Creatures. HarperCollins Publishers Ltd. pp. 118–125. ISBN   978-1-77554-179-0. Wikidata   Q114871191.
  8. ↑ "Atlas of Living Australia - Octopus tetricus (Gould, 1852)". Atlas of Living Australia . Retrieved 26 October 2014.
  9. 1 2 Gould, A.A. (1852). Mollusca of the United States Exploring Expedition under Captain Charles Wilkes. Mollusca of the Wilkes Expedition. Vol. 12. Philadelphia: Printed by C. Sherman. p. 474.
  10. ↑ Gould, A.A. (1856). United States exploring edition. Mollusca and Shells Atlas. Vol. 12. Philadelphia: Printed by C. Sherman. pp. plate 47.
  11. ↑ Johnson, Richard I. (1964-01-01). "The Recent Mollusca of Augustus Addison Gould". Bulletin of the United States National Museum (239): 1–182. doi:10.5479/SI.03629236.239.
  12. ↑ Voss, Nancy A.; Sweeney, M. J. (1998-01-01). "Systematics and Biogeography of cephalopods. Volume II". Smithsonian Contributions to Zoology (586): 277–599. doi:10.5479/SI.00810282.586.277.
  13. ↑ Amor, Michael D.; Norman, Mark D.; Cameron, Hayley E.; Strugnell, Jan (2014-06-25). "Allopatric speciation within a cryptic species complex of Australasian octopuses". PLOS ONE. 9 (6): e98982. Bibcode:2014PLoSO...998982A. doi: 10.1371/JOURNAL.PONE.0098982 . PMC   4070898 . PMID   24964133.
  14. 1 2 3 Ramos Castillejos JE (2015). Life-history and population dynamics of the range extending Octopus tetricus (Gould, 1852) in south-eastern Australia (Ph.D. thesis). University of Tasmania.
  15. ↑ Huffard CL; Godfrey-Smith P (2010). "Field observations of mating in Octopus tetricus Gould, 1852 and Amphioctopus marginatus (Taki, 1964) (Cephalopoda: Octopodidae)". Molluscan Research. 30 (2): 81–86. doi:10.11646/mr.30.2.3. S2CID   266214974 – via ResearchGate.
  16. 1 2 Spreitzenbarth, Stefan; Jeffs, Andrew (2020-09-15). "Egg survival and morphometric development of a merobenthic octopus, Octopus tetricus, embryos in an artificial octopus egg rearing system". Aquaculture. 526: 735389. Bibcode:2020Aquac.52635389S. doi:10.1016/j.aquaculture.2020.735389. ISSN   0044-8486. S2CID   219088008.
  17. ↑ Joll LM (1976). "Mating, egg-laying and hatching of Octopus tetricus (Mollusca: Cephalopoda) in the laboratory". Marine Biology. 36 (4): 327–333. Bibcode:1976MarBi..36..327J. doi:10.1007/bf00389194. ISSN   0025-3162. S2CID   83838409.
  18. 1 2 Ramos JE; Pecl GT; Moltschaniwskyj NA; et al. (2014). "Body size, growth and life span: implications for the polewards range shift of Octopus tetricus in south-eastern Australia". PLOS ONE. 9 (8): e103480. Bibcode:2014PLoSO...9j3480R. doi: 10.1371/journal.pone.0103480 . PMC   4121162 . PMID   25090250.
  19. ↑ Scheel D; Godfrey-Smith P; Lawrence M (2014-12-30). "Octopus tetricus (Mollusca: Cephalopoda) as an ecosystem engineer". Scientia Marina. 78 (4): 521–528. doi: 10.3989/scimar.04073.15A . ISSN   1886-8134.
  20. 1 2 Godfrey-Smith P; Lawrence M (2012-07-01). "Long-term high-density occupation of a site by Octopus tetricus and possible site modification due to foraging behavior". Marine and Freshwater Behaviour and Physiology. 45 (4): 1–8. Bibcode:2012MFBP...45....1G. doi:10.1080/10236244.2012.727617. ISSN   1023-6244. S2CID   83893501.
  21. ↑ Anderson TJ (April 30, 1997). "Habitat selection and shelter use by Octopus tetricus". Marine Ecology Progress Series. 150: 137–48. Bibcode:1997MEPS..150..137A. doi: 10.3354/meps150137 .
  22. 1 2 3 Scheel D; Chancellor S; Hing M; et al. (2017-07-04). "A second site occupied by Octopus tetricus at high densities, with notes on their ecology and behavior". Marine and Freshwater Behaviour and Physiology. 50 (4): 285–291. Bibcode:2017MFBP...50..285S. doi:10.1080/10236244.2017.1369851. ISSN   1023-6244. S2CID   89738642.
  23. ↑ Godfrey-Smith, Peter; Scheel, David; Chancellor, Stephanie; Linquist, Stefan; Lawrence, Matthew (2022). "In the line of fire: Debris throwing by wild octopuses". PLOS ONE. 17 (11): e0276482. Bibcode:2022PLoSO..1776482G. bioRxiv   10.1101/2021.08.18.456805 . doi: 10.1371/journal.pone.0276482 . PMC   9645608 . PMID   36350820.
  24. ↑ Morse P (2008). Female Mating Preference, Polyandry, and Paternity Bias in Octopus tetricus (Honors Thesis). University of Western Australia, Perth. pp. 1–97.
  25. ↑ Main D (28 January 2016). "Octopuses More Social Than Thought, Denizens of 'Octopolis' Prove". Newsweek. Retrieved 14 September 2017.
  26. ↑ Stokstad E (13 September 2017). "Scientists discover an underwater city full of gloomy octopuses". Sciencemag. Retrieved 14 September 2017.
  27. ↑ The IUCN Red List of Threatened Species 2018.1. 2018-07-05.
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