Australian Snubfin Orcaella Heinsohni Research Articles

Collation and review of sightings and distribution of three coastal dolphin species in waters of the Northern Territory, Australia.

On a global scale, the coastal waters of the Northern Territory (NT), Australia, are relatively undisturbed, but the pace and extent of coastal development is increasing. Three species of dolphin occur in these waters: the Australian snubfin Orcaella heinsohni, Indo-Pacific humpback Sousa chinensis and bottlenose Tursiops sp., but their distribution is poorly documented. To provide a broader distributional context and complement recent local-scale population studies (Palmer in press), we review the broader distribution of these coastal dolphins, via the collation of historic and contemporary data from sighting surveys, stranding and museum records, and a community sighting programme. Records spanned 1948 to 2010, with Sousa (44%) the most frequently recorded followed by Orcaella and Tursiops (both 28%). The compiled records indicate that the three species are widely distributed along the NT coast but with some apparent differences in habitat use. All species were recorded within 20 km of a major tidal river; but fewer than 3% of Tursiops records were from within tidal rivers, whereas nearly a quarter of Orcaella and Sousa records were as far as 20 to 50 km upstream. Differences in environmental settings between Orcaella and Sousa were less pronounced, but a lower proportion of Orcaella were recorded within 20 km of a river mouth. There are probable but unquantifiable biases in the record sources, but most records of dolphins were from estuaries, tidal rivers and coastal areas within 20 km of river mouths, and these sites probably represent important habitat for these species. The NT’s remote and relatively pristine waters likely hold significant subpopulations of all three species. The information provided here should aid future research efforts, however; further information on the dolphins’ population size, trend and structure are needed to resolve their conservation status at state and national jurisdictions, inform environmental impact assessments and species management.

Acoustic alarms elicit only subtle responses in the behaviour of tropical coastal dolphins in Queensland, Australia

Incidental bycatch in gill nets is the most serious of the global threats to marine mammals. Consequently, many management agencies wish to implement practical and efficient bycatch mitigation systems that both protect species of conservation concern and are readily adopted by fishermen. Australian snubfin Orcaella heinsohni and humpback dolphins Sousa chinensis occur in small fragmented populations along most of the remote coast of subtropical and tropical Australia, where they are caught in gillnet fisheries operated from small vessels. We experimentally investigated whether a commercially available acoustic alarm modified the behaviour of each of these species in the absence of a net. The movements and behaviour of both species changed subtly when the pingers were active, but the likelihood of the animals leaving an area was not significantly different from the controls. Our results suggest that this technological approach may not be effective in reducing the bycatch of these species. We suggest that further experimentation is unlikely to be cost effective and that government agencies should work with fishers and scientists to explore alternative mitigation measures.

Tropical inshore dolphins of north-western Australia: Unknown populations in a rapidly changing region.

Australian Snubfin Orcaella heinsohni, Indo-Pacific Humpback Sousa chinensis and Indo-Pacific Bottlenose Dolphins Tursiops aduncus inhabit Australia’s tropical north-western coastline, a region undergoing extensive port development associated with the massive expansion of the oil, gas and mining industries. The current lack of data on dolphin population sizes or trends precludes impact assessments of developments on these protected species. Furthermore, the Western Australian and Commonwealth Government conservation listings of tropical inshore dolphins do not reflect their international listings. From April to July, 2010, we conducted ad hoc boat-based surveys (n=55) of inshore delphinids at seven sites across north-western Australia from Coral Bay in the south (23.1°S: 113.8°E) to Cable Beach in the north (17.9°S: 122.2°E). We documented the locations of these three species from which we obtained photoidentification and biopsy data, as well as reports of Australian Snubfin Dolphin sightings from researchers and community groups. The data from this limited field effort confirm that Indo-Pacific Humpback and Indo-Pacific Bottlenose Dolphins occur in the waters adjacent to each north-western Australian urban centre and show that the range of the Australian Snubfin Dolphin extends considerably further south-west than previously reported. Given the scale of coastal developments and the vulnerability of isolated cetacean populations to fragmentation or extirpation, assessments of the viability of dolphin populations are required. Our data suggest that the Australian Snubfin, Indo-Pacific Humpback and Indo-Pacific Bottlenose Dolphins need to be considered as likely to be impacted by coastal developments across north-western Australia.

Coastal dolphins in north-western Australia: The need for re-evaluation of species listings and short-comings in the Environmental Impact Assessment process.

LITTLE is known about the distribution, abundance and behavioural ecology of dolphins in the tropical north-west of Australia. This region is remote, and until recently, has had a relatively low human population. Two of Australia’s tropical coastal dolphin species, the Australian Snubfin Orcaella heinsohni and Indo-Pacific Humpback Dolphins Sousa chinensis (“Snubfin Dolphin” and “Humpback Dolphin”, hereafter) are known to occur in the region. Australia-wide, the only scientific publications on these two species come from a few studies from eastern Queensland, where both species live in “populations” of 50–100 individuals (Parra et al. 2006a; Cagnazzi et al. 2009) that are genetically isolated from one another (Parra 2011); have small home ranges; and are found in near-shore areas, typically within 3- 5 km of the coastline (Parra 2006; Parra et al. 2002, 2004, 2006a,b; Cagnazzi et al. 2009). In eastern Australia, both species forage on coastal/estuarine fish and cephalopods, which is further evidence of their reliance on the near-shore environment (Parra and Jedensjö 2009). According to population sizes in Queensland, and the extent of potentially suitable habitat along the north-west coast, the total numbers in Western Australia are likely to be in the low thousands of individuals (i.e., < 5000). The combination of these life-history characteristics may render Snubfin and Humpback Dolphins particularly vulnerable to local extinctions due to human activities such as habitat modification and increased shipping and boating activity (Frankham 2005; O’Grady et al. 2006). In this Essay, we review the current extent of coastal developments in the waters of north-west Australia. Then we discuss the conservation and management implications of this in relation to coastal dolphins, particularly Snubfin and Humpback Dolphins. We also appraise the current, non-targeted methods being used to survey marine mammal populations for environmental impact assessments (EIAs), highlighting their inadequacy for coastal dolphins. Finally, we make recommendations that should improve government decision making processes for the long term conservation of these two species.