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. 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".
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 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), and soon thereafter a Dutch skipper had his observations of the then-unrecognised species published. 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.
Two scientists, Isabel Beasley of James Cook University and Peter Arnold of Museum of Tropical Queensland, took DNA samples from the population of dolphins off the coast of Townsville, Queensland, and sent them to the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, California. The results showed George Heinsohn was correct in his hypothesis that the Townsville population was a new species.
The holotype QM 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. Australian snubfin dolphins have a varied diet, eating a range of fish, shrimp, and cephalopods (squid, cuttlefish and octopus). They are found in small groups of about 2–6, but larger groups (up to 14 individuals) have also been observed. Populations are usually smaller than 150 individuals. Some instances of long-term sociability have been observed among individuals off the coast of Queensland, Australia. Grouping associations seem to be strongest among male individuals implying some potential correlation to reproductive strategy.
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. They produce clicks of short durations with high peaks, making their clicks distinguishable from other odontocetes.
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.
Australian snubfin dolphins have been observed to spit jets of water across the surface of the water as a potential feeding strategy. 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. They can be classified as opportunistic feeders and have been seen congregating to feed in groups.
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.
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. 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 of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II
Australian snubfin dolphins are also listed as "vulnerable" by the IUCN.
See also
- List of cetaceans
- Marine biology
- Environmental issues in Australia