Conservation biology of dolphins in coastal waters of the Northern Territory, Australia

• Main Author: Palmer, Carol
• Format: Thesis
• Language: unknown
• Published: Charles Darwin University 2014
• Subjects: Port Essington; Killer Whale
• Online Access: https://dx.doi.org/10.25913/5ebc874d30ca3; https://researchers.cdu.edu.au/en/studentTheses/conservation-biology-of-dolphins-in-coastal-waters-of-the-norther

In a global context, the tropical coastal waters around much of northern Australia are exceptional in their relatively unmodified condition, due largely to the limited amount of coastal development and relatively low human population size in coastal lands. These waters offer a significant opportunity for the conservation of coastal biodiversity. However, increasing development pressures may jeopardise this opportunity and adding to this risk there is little information on distribution, population size and trends for much of the marine biodiversity in the region. This data deficiency has constrained the assessment of the conservation status of marine species and hence compromised conservation planning, management and security. This study assessed aspects of the status of three species of coastal dolphin – the Australian snubfin (Orcaella heinsohni), the recently described Australian humpback (Sousa sahulensis) and bottlenose (either or both Tursiops truncatus or T. aduncus) – in coastal waters of the Northern Territory (NT), Australia. Serendipitously, I also considered aspects of the status and distribution of the false killer whale (Pseudorca crassidens), a delphinid species that uses NT coastal waters to a much greater extent than was previously known. This study helped clarify the taxonomy and distribution of Orcaella in these waters, documented the broad distributional patterns of the three dolphin species in this region, and provided the first estimates of abundance and apparent survival for all three species for a site in monsoonal northern Australia. The three species were found to be widely distributed along the Northern Territory coast, but showed some significant differences in habitat use. At my main study site in Port Essington, the population sizes of the three species were determined by Pollock’s robust capture–recapture design modeling over 2.9 years. The estimated number of individuals varied per sampling episode from 136 (s.e. 62) to 222 (s.e. 48) for Orcaella, 48 (s.e. 17) to 207 (s.e. 65) for Sousa and 34 (s.e. 16) to 75 (s.e. 26) for Tursiops. Apparent annual survival for Orcaella was 0.81 (s.e. 0.11), Sousa 0.59 (s.e. 0.12) and Tursiops 0.51 (s.e. 0.17). Satellite tracking of four false killer whales demonstrated that this species is recorded in these coastal waters, but at a very different scale to the coastal dolphins. The study findings are interpreted with respect to the conservation status of the four species, and I draw some recommendations for their conservation management.