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Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia

Palmer, Carol, Brooks, Lyndon, Parra, Guido, Rogers, Tracey, Glasgow, Debra and Woinarski, John (2014). Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia. Wildlife Research,41(1):35-45.

Document type: Journal Article
Citation counts: Scopus Citation Count Cited 0 times in Scopus Article

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IRMA ID 84376995xPUB36
Title Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia
Author Palmer, Carol
Brooks, Lyndon
Parra, Guido
Rogers, Tracey
Glasgow, Debra
Woinarski, John
Journal Name Wildlife Research
Publication Date 2014
Volume Number 41
Issue Number 1
ISSN 1035-3712   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-84901376889
Start Page 35
End Page 45
Total Pages 11
Place of Publication Australia
Publisher C S I R O Publishing
Field of Research ENVIRONMENTAL SCIENCES
HERDC Category C1 - Journal Article (DIISR)
Abstract Context: Three dolphin species occur in coastal waters of monsoonal northern Australia: the Australian snubfin (Orcaella heinsohni), humpback (Sousa sp.) and the bottlenose (Tursiops sp.). Their overall population size and trends are poorly known, and their conservation status has been difficult to resolve, but can be expected to deteriorate with likely increased development pressures.

Aims: We sought to provide an estimate of abundance, and apparent survival, of the three dolphin species at the largely undeveloped harbour of Port Essington (325 km2), Northern Territory, with repeated sampling over a 2.9-year period. Given increasing obligations to undertake population assessments for impact studies at proposed development sites, we assess the strengths and limitations of a systematic sampling program.

Methods: We used photo-identification data collected during systematic boat-based transect surveys undertaken from 2008 to 2010 and Pollock’s robust capture–recapture design model.

Key results: Total abundance estimates for the three species were variable across different sampling periods. The estimated number of individuals in the sampled area varied per sampling episode from 136 (s.e. 62) to 222 (s.e. 48) for snubfin, from 48 (s.e. 7) to 207 (s.e. 14) for humpbacks and from 34 (s.e. 6) to 75 (s.e. 9) for bottlenose dolphins. Apparent survival was estimated for snubfin at 0.81 (s.e. 0.11), humpbacks at 0.59 (s.e. 0.12) and bottlenose at 0.51 (s.e. 0.17) per annum.

Key conclusions: (1) The values derived here provide some of the only estimates of local population size for these species across monsoonal northern Australia; (2) population-size estimates varied considerably among seasons or sampling episodes; (3) the low apparent survival probabilities indicated that many individuals may move at scales larger than the study area; (4) density of snubfin and humpback dolphins in the present study area exceeded the few other estimates available for these species elsewhere in Australia.

Implications: The present study provided the first baseline estimates of abundance and apparent survival for three coastal dolphin species in monsoonal northern Australia. Such information is becoming increasingly important as development pressures intensify in coastal areas. Sampling protocols for future monitoring and impact assessment need an enhanced consideration of seasonality and scale issues.
Keywords Australian snubfin
bottlenose
capture–recapture
Indo-Pacific humpback
Orcaella heinsohni
photo identification
robust design
Sousa chinensis
Tursiops sp.
DOI http://dx.doi.org/10.1071/WR14031   (check subscription with CDU E-Gateway service for CDU Staff and Students  check subscription with CDU E-Gateway in new window)
 
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