The Australian snubfin dolphin (Orcaella heinsohni) is a dolphin found off the northern coasts of Australia. It closely resembles the Irrawaddy dolphin (of the same genus, Orcaella) and was not described as a separate species until 2005. The closest relative to the genus Orcaella is the killer whale, Orcinus orca.[citation needed] The Australian snubfin has three colors on its skin, while the Irrawaddy dolphin only has two. The skull and the fins also show minor differences between the two species.
Taxonomy
The taxonomic specific name, heinsohni, was chosen in honour of George Heinsohn, an Australian biologist who worked at James Cook University, "for his pioneering work on northeast Australian odontocetes, including the collection and initial analysis of Orcaella heinsohni specimens which form the basis for much of our knowledge of the new species".[2]
New species of large mammals are quite rarely described nowadays, and those that are usually are from remote areas— such as the saola - or are otherwise rarely encountered, see for example Perrin's beaked whale, or the spade-toothed whale, which is only known from two complete specimens and a few bones cast ashore. In fact, the Australian snubfin was the first new dolphin species to be described in 56 years, but was followed, in 2011, by the discovery and description of the Burrunan dolphin (T. australis), also from the Australian continent. The Australian snubfin dolphin is unusual among recently described mammals in that a population is accessible for scientific study.
Nonetheless, the existence of snubfin dolphins in the waters of northern Australia had only become known to western scientists in 1948, when a skull was collected at Melville Bay (Gove Peninsula, Northern Territory). This individual apparently had been caught and eaten by aboriginals. However, the discovery remained unnoted until discussed by Johnson (1964),[3] and soon thereafter a Dutchskipper had his observations of the then-unrecognised species published.[4] The common name "snubfin dolphin" was suggested in 1981 and highlights a diagnostic external character and has previously been used in field guides for identification.[5]
The holotypeQM JM4721 (JUCU MM61) is the skull and some other bones of an adult male found drowned in a shark net at Horseshoe Bay, Queensland, on 21 April 1972. It was about 11 years old at the time of its death.[2]
Description
A species of delphinid in the genus, Orcaella, which contains one other species, the Irrawaddy dolphinOrcaella brevirostris, O. heinsohni females can reach lengths of 230cm (91in) and males can reach 270cm (110in).[6] Australian snubfin dolphins are subtly tricoloured: brownish on the top, lighter brown along the sides, and a white belly; the Irrawaddy dolphin, on the other hand, is uniformly slate grey except for the white belly. The new species has a rounded forehead, very unlike other dolphin species in Australia, and the very small, "snubby" dorsal fin distinguishes it from other dolphins in its range. The lack of a groove on each side of the back and the presence of a neck crease further distinguishes this species from its relative. Tail flukes also have an identifiable jagged trailing edge that can help distinguish it from other species of delphinids.
The number of nasal bones in each side of a snub fin dolphin's skull vertex varies from none to six. There is a poorly developed mesthemoid plate. In the upper jaw there are roughly 11–22 teeth in each half, and in the lower jaw there are roughly 14–19 teeth in each half.[5]
Life history
In a study of Australian snubfin dolphins consisting of 18 individuals, it was determined the approximate life span is around 30 years. However, since sightings are so rare, a lot remains unknown about many about this species. Gestation is estimated to be around 11 months based on rates of similar species.[7]
Behavior
Much remains unknown about the ecology and behaviours of the Australian snubfin dolphin.[8] Australian snubfin dolphins have a varied diet, eating a range of fish, shrimp, and cephalopods (squid, cuttlefish and octopus).[9] They are found in small groups of about 2–6, but larger groups (up to 14 individuals) have also been observed.[10] Populations are usually smaller than 150 individuals.[11] Some instances of long-term sociability have been observed among individuals off the coast of Queensland, Australia.[7] Grouping associations seem to be strongest among male individuals implying some potential correlation to reproductive strategy.[7] Additionally, there was an observation of snubfin dolphins displaying mating courtship between Australian humpback dolphins.[12]
Both the Australian snubfin dolphin and the Australian humpback dolphin co-occur throughout much of the tropical Northern waters of Australia, and have similar vocal repertoires consisting of click trains, burst pulses, and whistles.[8] As a member of the suborder odontoceti, much of these vocalizations are thought to be associated with echolocation for both navigation and foraging.[13] They produce clicks of short durations with high peaks, making their clicks distinguishable from other odontocetes.[14]
Snub fin dolphins have also been observed interacting with Australian humpback dolphins, and one case of a hybrid between the two species was documented using DNA analysis in 2014.[15]
Australian snubfin dolphins have been observed to spit jets of water across the surface of the water as a potential feeding strategy.[7] Jets of water appear to cause fish to leap from the water towards the dolphin, making them easier prey targets.
Feeding
Off the coast of Queensland, Australia, the Australian snubfin dolphin predominantly feeds in coastal-estuarine waters.[16] There is a predominance of feeding activity by rivers and areas off the coast of Cleveland bay. Australian snubfin dolphins have also been seen foraging and then following passing by fish trawlers to capitalize on an opportunity for prey.[17] They can be classified as opportunistic feeders and have been seen congregating to feed in groups.[16] Being opportunistic feeders snubfins consume a large array of prey items.[16] Snubfin dolphin consume a wide array of prey, that can be narrowed down to coastal, estuarine, and reef-associated fishes throughout the water column and at the bottom.[16] The most common prey items by species are cardinal fish (Apogon), proceeded by the cuttlefish (Sepia), the squid Uroteuthis (Photololigo), and the toothpony fish (Gazza).[17] Another big part of the snubfin diet are cephalopods.[17]
Range and status
The snubfin dolphin is considered endemic to Australia. In the Pacific Ocean off Townsville, about 200 individual snubfin dolphins were found. The range of the species is expected to extend to Papua New Guinea; that is, O. heinsohni is endemic to the northern half of the Sahul Shelf, but the majority live in Australian waters. They are found all along the northern coasts of Australia, from Broome, Western Australia, to the Brisbane River in Southeast Queensland.[10] They are not thought to be common, and are being given a high conservation priority. Australian snubfin dolphins are currently listed as "vulnerable" by the IUCN.[11]
Habitat range has primarily been determined through visual sightings and stranding data, limiting the range to areas accessible by humans. Passive acoustic monitoring methods are being deployed to attempt to more accurately determine the range of these animals by listening for their distinctive echolocation clicks.[14]
Threats
Although some hunting by indigenous people occurs (as evidenced by the 1948 specimen), this is likely to be insignificant compared to other threats such as drowning in sharknets and fishing gear. Snubfins are particularly at risk from incidental capture in gillnets, which are often placed in near-shore areas and near the mouths of rivers, where these dolphins are more likely to be found.[11] Although it is not known how many dolphins die in this manner, it is considered to be the greatest threat to populations in Papua New Guinea. Anti-shark nets and drumlines put in place for Queensland's shark control program are also a significant threat to snubfins, with about 1.8 snubfin dolphins killed every year between 1997 and 2011.[11]
The coastal zones along the Australian snubfin dolphin's range have been highly modified for mining and agricultural purposes as well as ports, aquaculture and residential development. Land reclamation, vessel traffic and construction results in the degradation of the snubfin's natural habitat through increased noise, lower water quality and a reduction in food supply, in addition to direct loss of habitat areas due to land reclamation. This can result in decreased survival rates and/or emigration in search of better resources.[11]
Pollution is another threat to snubfin dolphins, as the water discharge from rivers in the dolphins' Australian range are contaminated by industrial and agricultural runoff. The snubfin dolphins' strong site fidelity means they are likely exposed to pollutants on a daily basis. Indeed, one study of snubfins on the Great Barrier Reef found levels of polychlorinated biphenyls (PCBs) far exceeding the thresholds for small cetaceans, over which reproductive anomalies and immunosuppression can occur.[18] Periodic floods present a temporary threat to snubfin dolphins in that they result in an increase in freshwater discharge, heavy metals, nutrients, sediment and pesticides in coastal areas. Increases in floods, cyclone severity, storm surges and sea surface temperatures due to climate change will likely also affect the habitat and future food supply of snubfin dolphins.[19] As a result of the cumulative effects of drowning as bycatch and habitat loss and degradation, the Australian snubfin dolphin population is believed to be decreasing and is likely to meet the criteria for IUCN's "endangered" status in the near future.[11]
As small populations are more vulnerable to extinction due to the small numbers and low genetic diversity, the snubfin dolphin is at significant risk in their human populated habitat.[20] The insufficient data on the species poses additional threat as their general ecology is not fully understood.
Conservation
The Australian snubfin dolphin is listed on Appendix II[21] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II[21] as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.[22]
Australian snubfin dolphins are also listed as "vulnerable" by the IUCN.[11]
In addition, Australian snubfin dolphins are covered by Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MOU).[23]
The Indo-Pacific humpback dolphin is a species of humpback dolphin inhabiting coastal waters of the eastern Indian and western Pacific Oceans. This species is often referred to as the Chinese white dolphin in mainland China, Macau, Hong Kong, Singapore and Taiwan as a common name. Some biologists regard the Indo-Pacific dolphin as a subspecies of the Indian Ocean humpback dolphin which ranges from East Africa to India. However, DNA testing studies have shown that the two are distinct species. A new species, the Australian humpback dolphin, was split off from S. chinensis and recognized as a distinct species in 2014. Nevertheless, there are still several unresolved issues in differentiation of the Indian Ocean-type and Indo-Pacific-type humpback dolphins.
Risso's dolphin is a dolphin, the only species of the genus Grampus. Some of the closest related species to these dolphins include: pilot whales, pygmy killer whales, melon-headed whales, and false killer whales.
Blainville's beaked whale, or the dense-beaked whale, is believed to be the widest ranging mesoplodont whale. The French zoologist Henri de Blainville first described the species in 1817 from a small piece of jaw — the heaviest bone he had ever come across — which resulted in the name densirostris. Off the northeastern Bahamas, the animals are particularly well documented, and a photo identification project started sometime after 2002.
The Irrawaddy dolphin is a euryhaline species of oceanic dolphin found in scattered subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia. It closely resembles the Australian snubfin dolphin, which was not described as a separate species until 2005. It has a slate blue to a slate gray color. Although found in much of the riverine and marine zones of South and Southeast Asia, the only concentrated lagoon populations are found in Chilika Lake in Odisha, India and Songkhla Lake in southern Thailand.
The snubfin dolphins (Orcaella) are a genus of cetaceans containing two members: the Irrawaddy dolphin and the Australian snubfin dolphin. The genus was long believed to be monotypic with the only species being the Irrawaddy dolphin; however, in 2005, supposed Irrawaddy dolphin populations inhabiting the Australian/New Guinean regions were found to be significantly different and were declared a separate new species named the Australian snubfin dolphin.
The false killer whale is a species of oceanic dolphin that is the only extant representative of the genus Pseudorca. It is found in oceans worldwide but mainly in tropical regions. It was first described in 1846 as a species of porpoise based on a skull, which was revised when the first carcasses were observed in 1861. The name "false killer whale" comes from having a skull similar to the orca, or killer whale.
The Indo-Pacific bottlenose dolphin is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb). It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. Its back is dark grey and its belly is lighter grey or nearly white with grey spots.
Humpback dolphins are members of the genus Sousa. These dolphins are characterized by the conspicuous humps and elongated dorsal fins found on the backs of adults of the species. Humpback dolphins inhabit shallow nearshore waters along coastlines across Australia, Africa, and Asia. Their preference for these habitats exposes them to various human activities such as fisheries entanglement, boat traffic, pollution, and habitat loss. Despite these risks, their nearshore presence facilitates easy observation from land.
The Atlantic humpback dolphin is a species of humpback dolphin that is found in coastal areas of West Africa.
The Indian Ocean humpback dolphin is a member of the Delphinidae family occupying coastal areas ranging from Southern Africa to Western Indochina. The Indo-Pacific humpback dolphin was formerly included within the same species, but a 2014 study revealed them to be a separate species.
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.
The northern right whale dolphin is a small, slender species of cetacean found in the cold and temperate waters of the North Pacific Ocean. Lacking a dorsal fin, and appearing superficially porpoise-like, it is one of the two species of right whale dolphin.
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.
The spinner dolphin is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a member of the family Delphinidae of toothed whales.
Cetacean surfacing behaviour is a grouping of movement types that cetaceans make at the water's surface in addition to breathing. Cetaceans have developed and use surface behaviours for many functions such as display, feeding and communication. All regularly observed members of the order Cetacea, including whales, dolphins and porpoises, show a range of surfacing behaviours.
Cetacean bycatch is the accidental capture of non-target cetacean species such as dolphins, porpoises, and whales by fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets.
The Australian humpback dolphin is a species of humpback dolphin and the fourth recognized humpback dolphin species chronologically. The specific name sahulensis is derived from the Sahul Shelf, located between northern Australia and southern New Guinea, where the Australian humpback dolphins occur.
Swatch of No Ground Marine Protected Area is a protected area of Bangladesh in the Bay of Bengal. The reserve covers an area of 1,636 km2 (632 sq mi).
1 2 Beasley, Isabel; Robertson, Kelly M.; Arnold, Peter (July 2005). "Description of a new dolphin, the Australian snubfin dolphin Orcaella heinsohni sp. n. (Cetacea, Delphinidae)". Marine Mammal Science. 21 (3): 365–400. doi:10.1111/j.1748-7692.2005.tb01239.x.
↑ Johnson, D.P. (1964). "Mammals of the Arnhem Land expedition". In Specht, R.L. (ed.). Records of the American-Australian scientific expedition to Arnhem Land. Volume 4 Zoology. Melbourne, Australia: Melbourne University Press. pp.427–515.
↑ Mörzer Bruyns, W.F.J. (1966). "Some notes on the Irrawaddy dolphin, Orcaella brevirostris (Owen 1866)". Zeitschrift für Säugetierkunde. 31: 367–372.
↑ Cranford, Ted W. (2000). "In Search of Impulse Sound Sources in Odontocetes". Hearing by Whales and Dolphins. Springer Handbook of Auditory Research. Vol.12. New York, NY: Springer New York. pp.109–155. doi:10.1007/978-1-4612-1150-1_3. ISBN9781461270249.
1 2 de Freitas, Mafalda; Smith, Joshua N.; Jensen, Frants H.; Beedholm, Kristian; Madsen, Peter T. (April 2018). "Echolocation click source parameters of Australian snubfin dolphins (Orcaella heinsohni)". The Journal of the Acoustical Society of America. 143 (4): 2564–2569. Bibcode:2018ASAJ..143.2564D. doi:10.1121/1.5034174. hdl:1912/10497. PMID29716291.
↑ Lawler, I.; Parra G.J.; Noad M. (2007). "Vulnerability of marine mammals in the Great Barrier Reef to climate change". In Johnson, J.E.; Marshall, P.A. (eds.). Climate change and the Great Barrier Reef: a vulnerability assessment. Townsville, Queensland, Australia: Great Barrier Reef Marine Park Authority and Australian Greenhouse Office.
↑ Parra, Guido J.; Corkeron, Peter J.; Marsh, Helene (1 April 2006). "Population sizes, site fidelity and residence patterns of Australian snubfin and Indo-Pacific humpback dolphins: Implications for conservation". Biological Conservation. 129 (2): 167–180. doi:10.1016/j.biocon.2005.10.031. ISSN0006-3207.
1 2 "Appendix IIArchived 11 June 2011 at the Wayback Machine " of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
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