Discovering Australia’s snubfin dolphin

Geographical location:

Asia/Pacific > Australia/New-Zealand > Australia

Australasian snubfin dolphin. Australia.
© WWF Australia / Guido Parra

Summary

A new species of dolphin was found in Australia’s northern waters in 2005. The discovery of the Australian snubfin – previously thought to be an Irrawaddy dolphin – is extremely rare, particularly when many species today are heading towards extinction. Unlike other dolphin species found in Australia, the snubfin has a rounded forehead and a very small, “snubby” dorsal fin. Like many dolphin species, they are threatened by habitat destruction and accidental entanglement in fishing gear.

A WWF-supported project aims to get a better understanding of the ecology of this relatively unknown species in order improve coastal dolphin conservation in northern Australia.

Background

Coastal dolphins are the most threatened dolphins worldwide (Thompson et al 2000) and knowledge about the ecology and anthropogenic threats to Australia's coastal dolphins is scarce, particularly for rare tropical species such as the Australian snubfin (Orcaella heinsohni) and the Indo-Pacific Humpback (Sousa chinensis).

In the Pacific Ocean off Townsville, about 200 individual snubfin dolphins were found. It is expected that the range of the species extends into Papua New Guinea, but that the majority live in northern Australian waters. They are not thought to be common and are being given a high conservation priority.

Whilst the snubfin dolphin was originally thought to be an Irrawaddy dolphin (Orcaella brevirostris, recent morphological and genetic studies of the genus Orcaella showed that populations in north-eastern Australia are a separate species (Orcaella heinsohni). It was also found that the Australian snubfin dolphin is tri-coloured, while the Irrawaddy dolphin only has 2 colours on its skin. However, as only one genetic sample from the NT was included in the analysis (Beasley et al 2005) the taxonomic identity of Northern Territory Orcaella remains uncertain. There are similar doubts about species level taxonomy of Sousa (Jefferson and Van Waerebeek 2004).

Very little is known about the snubfin dolphin. Recent studies in Queensland have shown that it is a potentially endemic to Australia. Unlike many other dolphins, the snubfin normally occurs in small groups, is shy and does not bow ride. The species is strongly linked to the mouths of tidal rivers within 10km of land, in water less than 10m deep and within 10km of the nearest river mouth. Coastal dolphins are the most threatened dolphins worldwide and effective conservation actions are limited by a lack of knowledge about the ecology of the species.

For NT coastal waters there is little or no baseline ecological information for either species. Primary threats to cetaceans include incidental mortality as a result of fishing activities but particularly the use of gill nets (Hale et al 2004). Large numbers of dolphins and porpoises die in gill nets worldwide, usually as bycatch.

The impact of bycatch on populations can be particularly problematical for marine mammals because they are long-lived, have slow growth rates and low fecundity (Cox et al 2003). In the NT, both Orcaella and Sousa distributions are almost completely contained within the commercial NT Barramundi gillnet fisheries and coastal netters areas (NT Department of Primary Industries and Mines 2005).

One of the major obstacles for effective on-ground management in NT waters is a lack of knowledge about the basic ecology of the Australian snubfin and Indo-Pacific humpback dolphins and an understanding of the threats they face. Importantly though, the relatively pristine and undeveloped NT coastline could hold secure populations for both species and be critically important for the longterm conservation of the species.

A detailed understanding of the ecology, distribution, demography, population genetics and the effects of commercial gillnetting operations is essential to the effective conservation of the Australian snubfin and Indo-Pacific humpback dolphins. However, no detailed cetacean research has ever been undertaken in the NT, and such fundamental information is lacking.

This project is a joint project between the Northern Territory Government, indigenous land councils, and WWF Australia.

Objectives

The project will be undertaken at 4 study sites: Darwin Harbour/Shoal Bay; Kakadu National Park; Coburg Peninsula; north-east (NE) Arnhem Land (Caddell Strait, Buckingham and Arnhem Bays)

1) Clarify the taxonomic status of north-western populations of Orcaella and Sousa particularly whether north-western populations are genetically distinct species (or sub-species).

Tissue sampling via non-lethal methods will be carried out opportunistically during boat-based surveys across the 4 study sites. DNA will be extracted from tissue samples from both species using standard procedures and nucleotide sequences from the mitochondrial control region using the primers of Beasley et al 2005 for Orcaella and for Sousa. Analysis will be undertaken using the BioScience North Australia laboratory at the Arafura Timor Research Facility.

Groups involved: Biodiversity Conservation Division, Kakadu National Park, Northern Territory (NT) Parks and Wildlife Service (Coburg Marine Park) and the Gumurr Marthakal Rangers (NE Arnhem Land)

2) Develop abundance estimates, identify spatial patterns and habitat preferences at 2 sites in the NT: Darwin Harbour/Shoal Bay and the Alligator Rivers Region, Kakadu National Park.

Monthly monitoring will develop population estimates, and investigate trends in abundance, site fidelity and movement patterns by monthly boat-based transect surveys. Photo-identification techniques and mark/recapture analysis will be used, based on methodology developed by Parra (2006) and Stensland et al (2006).

Groups involved: Biodiversity Conservation Division, Kakadu National Park, NT Parks and Wildlife Service.

3) Risk analysis and potential impact of gill net fisheries on local populations of coastal dolphin.

Working collaboratively with the NT Barramundi Fisheries and the Seafood Council, assess hotspot areas where both dolphin species and gillnetting overlap (the Alligator Rivers Region is a good study site for this component). Effort data, and interactions/mortality information combined with abundance estimates will be used to carry out a risk analysis of the potential impacts of the gillnet fisheries on local populations of coastal dolphins.

Groups involved: Biodiversity Conservation Division, NT Fisheries, Seafood Council of the NT

4) Spatial distribution of Orcaella and Sousa in NT waters and the implications for marine planning.

Desktop study and collation including development of a spatial database incorporating cetacean sightings, distribution, habitats, gillnetting risk analysis and hotspot data gathered from previous records and during this study. This information will:
- Aid in the identification of important habitat for both species.
- Identify areas where there could be potential conflict with gillnetting operations.
- Identify areas where the local populations are most likely to contribute to the long-term survival of both species in NT waters.

Solution

This project will collect baseline ecological and genetic data as a basis for improved coastal dolphin conservation and marine conservation planning in northern Australia. Baseline surveys will be completed by December 2008.

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