New Publication: Demographic characteristics of Australian humpback dolphins reveal important habitat toward the south-western limit of their range

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We are delighted to bring to your attention a recent paper led by PhD Candidate Tim Hunt from Flinders University, in collaboration with colleagues from the University of Western Australia and Murdoch University, published in Endangered Species Research. The title of the paper is:

Demographic characteristics of Australian humpback dolphins reveal important habitat toward the southwestern limit of their range

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.

Left: North West Cape (NWC) study site, including vessel launch sites (Tantabiddi, Bundegi, and Exmouth) and opposing zigzag line transect sampling design (2 × 93 km in length). Right: Western Australia, indicating the location of the NWC, Pilbara region, and Australian humpback dolphin distribution

Left: North West Cape (NWC) study site, including vessel launch sites (Tantabiddi, Bundegi, and Exmouth) and opposing zigzag line transect sampling design (2 × 93 km in length). Right: Western Australia, indicating the location of the NWC, Pilbara region, and Australian humpback dolphin distribution.

 

Cumulative discovery curve of identified Australian humpback dolphins (n = 98) within the North West Cape study area over the 2013 (May to October), 2014 (April to October) and 2015 (May to October) survey periods (total 195 d). Vertical bars represent the number of survey effort hours during each month of study. Diamond symbols indicate separation of the 6 primary periods throughout the entire survey period. Vertical dotted lines indicate separation of yearly survey periods

Cumulative discovery curve of identified Australian humpback dolphins (n = 98) within the North West Cape study area over the 2013 (May to October), 2014 (April to October) and 2015 (May to October) survey periods (total 195 d).  Vertical bars represent the number of survey effort hours during each month of study. Diamond symbols indicate separation of the 6 primary periods throughout the entire survey period. Vertical dotted lines indicate separation of yearly survey periods.

 

Download the paper: The article can be downloaded freely HERE, or alternatively, please email Tim for a PDF at 

For further information on humpback dolphins in Exmouth, see also following papers::

  • Brown, A., Bejder, L., Cagnazzi, D., Parra, G. and Allen, S.J. 2012. The North West Cape, Western Australia: a potential hotspot for Indo-Pacific humpback dolphins Sousa chinensis? Pacific Conservation Biology 18: 240-246. doi: 10.1071/PC120240
  • Brown, A.M., Kopps, A.M., Allen, S.J., Bejder, L., Littleford-Colquhoun, B., Parra, G.J., Cagnazzi, D., Thiele, D., Palmer, C. and Frère, C.H. 2014. Population differentiation and hybridisation of Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins in north-western Australia. PLoS One 9: e101427. doi: 10.1371/journal.pone.0101427
  • Brown, A.M., Bejder, L., Parra, G.J., Cagnazzi, D., Hunt, T., Smith, J.L. and Allen, S.J. 2016. Sexual dimorphism and geographic variation in dorsal fin features of Australian humpback dolphins, Sousa sahulensis. Advances in Marine Biology 73: 273-314. doi: 10.1016/bs.amb.2015.08.002

 

Lars Bejder PhD
Lars Bejder PhD
Professor Lars Bejder PhD is the Research Leader of the Murdoch University Cetacean Research Unit.
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