Dear MARMAM readers,

New findings suggest that the North West Cape (NWC) in Western Australia's Ningaloo Reef region, some 1500 km north of Perth, is home to one of the largest populations of the threatened Australian humpback dolphin (Sousa sahulensis). About 130 individuals inhabit the 130 km² study area, and at approximately 1 humpback dolphin per km², this density is the highest recorded for this species.

The research paper, titled Demographic characteristics of Australian humpback dolphins reveal important habitat toward the southwestern limit of their range, has been published in the international journal Endangered Species Research. The article is open access and can be downloaded at: http://www.int-res.com/abstracts/esr/v32/p71-88/

The study, the North West Cape Dolphin Research Project, was made possible through collaboration with Murdoch University, and funds from The Australian Marine Mammal Centre and the Winifred Violet Scott Charitable Trust.

Publication details:

Hunt TN, Bejder L, Allen SJ, Rankin RW, Hanf D, Parra GJ. 2017. Demographic characteristics of Australian humpback dolphins reveal important habitat toward the southwestern limit of their range. Endangered Species Research 32:71-88. https://doi.org/10.3354/esr00784 

Abstract

The paucity of information on the recently described Australian humpback dolphin Sousa sahulensis has hindered assessment of its conservation status. Here, we applied capture-recapture models to photo-identification data collected during boat-based surveys between 2013 and 2015 to estimate the abundance, site fidelity and residence patterns of Australian humpback dolphins around the North West Cape (NWC), Western Australia. Using Pollock’s closed robust design, abundance estimates varied from 65 to 102 individuals, and POPAN open modelling yielded a super-population size of 129 individuals in the 130 km² study area. At approximately 1 humpback dolphin per km², this density is the highest recorded for this species. Temporary emigration was Markovian, suggesting seasonal movement in and out of the study area. Hierarchical clustering showed that 63% of individuals identified exhibited high levels of site fidelity. Analysis of lagged identification rates indicated dolphins use the study area regularly, following a movement model characterised by emigration and re-immigration. These density, site fidelity and residence patterns indicate that the NWC is an important habitat toward the southwestern limit of this species’ range. Much of the NWC study area lies within a Marine Protected Area, offering a regulatory framework on which to base the management of human activities with the potential to impact this threatened species. Our methods provide a methodological framework to be used in future environmental impact assessments, and our findings represent a baseline from which to develop long-term studies to gain a more complete understanding of Australian humpback dolphin population dynamics.

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Tim Hunt

PhD Candidate (Part-Time, External)

Cetacean Ecology, Behaviour and Evolution Lab (CEBEL)

School of Biological Sciences

Flinders University of South Australia

( Mob +61 (0)418 946 558| * tim.hunt@flinders.edu.au

: www.cebel.org.au & www.facebook.com/CEBELresearch