1 Marine Ecosystems, Flora and Fauna Division, Department of Land Resource Management, PO Box 496, Palmerston Northern Territory, 0831, Australia. 2 Research Institute for the Environment and Livelihoods, Charles Darwin University, Northern Territory, Australia 0909. 3 Cetacean Ecology, Behaviour and Evolution Lab, School of Biological Sciences, Flinders University, GPO Box 2100 Adelaide, South Australia 5001. 4 South Australian Research and Development Institute (Aquatic Sciences) PO Box 120, Henley Beach, South Australia 5022. 5 Evolution & Ecology Research Centre, School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia. PACIFIC CONSERVATION BIOLOGY Vol. 20(1): 116–125. Surrey Beatty & Sons, Sydney. 2014. Collation and review of sightings and distribution of three coastal dolphin species in waters of the Northern Territory, Australia CAROL PALMER 1, 2 , GUIDO J. PARRA 3, 4 , TRACEY ROGERS 5 and JOHN WOINARSKI 2 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. Key words: delphinid distribution, conservation status, Australian snubfin, Indo-Pacific humpback, bottlenose, coastal development INTRODUCTION ACROSS most of their global distribution, coastal and river dolphins are now exposed to an increasing range and intensity of anthropogenic activities (Borobia et al., 1991; Thompson et al., 2000; Kreb and Budiono, 2005; Cantor et al., 2011), and several species are now among the world’s most threatened mammals (e.g., Jaramillo-Legorreta et al., 2007, Turvey et al., 2007). Anthropogenic pressures include reduced freshwater outflow to estuaries, underwater noise, habitat loss, fisheries interactions, contamination from industrial, municipal and agriculture discharge, tourism and climate change (Constantine et al. 2004; Lusseau et al.2006; Wang et al., 2007; Dungan et al., 2011). By global standards, the coastal waters of Australia are relatively unmodified (Halpern et al., 2008; Edyvane and Dethmers 2010) and particularly in remote northern Australia, this may allow conservation opportunities to study the ecology of coastal dolphins in natural settings. It also allows for the description of a baseline condition, to inform future management of which environmental impact assessment is one aspect. There are now increasing prospects and proposals for development in coastal waters of northern Australia, and consequently some concerns about the conservation of the three species of coastal dolphins occurring in these waters (Parra et al., 2006a; Allen et al., 2012; Bejder et al., 2012; Cagnazzi et al., 2013). These species are the Australian snubfin dolphin (Orcaella heinsohni Beasley et al., 2005) (hereafter referred to as snubfin), Indo-Pacific humpback dolphin (Sousa chinensis Osbeck, 1765) (hereafter referred to as humpback) and bottlenose dolphin Tursiops sp. (hereafter referred to as bottlenose). In the most recent global assessment of conservation status, snubfin and humpback are listed as ‘Near Threatened’ (Reeves et al., 2008a, b); The bottlenose Tursiops aduncus is listed as ‘Data Deficient’ and T. truncatus is listed as ‘Least Concern’ (Hammond et al., 2008a, b). In the Northern Territory (NT) the conservation status of snubfin and humpback was re-assessed in 2012, with change from the previous status of Least Concern to Data Deficient: bottlenose (T. aduncus and T. truncatus) remained Least Concern. Despite conservation concerns, comprehensive information on the ecology of these species in Australia is available only for a few selected areas along Queensland’s east coast (Corkeron et al.,