Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
RESEARCH ARTICLE

A robust baseline for bottlenose dolphin abundance in coastal Moreton Bay: a large carnivore living in a region of escalating anthropogenic impacts

Vimoksalehi Lukoschek A C D and B. Louise Chilvers B
+ Author Affiliations
- Author Affiliations

A School of Earth and Environmental Sciences, James Cook University, Townsville, QLD 4811, Australia.

B Department of Conservation, PO Box 10-420, Wellington, New Zealand.

C Present address: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA.

D Corresponding author. Email: v.lukoschek@uci.edu

Wildlife Research 35(7) 593-605 https://doi.org/10.1071/WR07021
Submitted: 20 February 2007  Accepted: 10 June 2008   Published: 17 November 2008

Abstract

Marine megafauna populations in coastal waters are increasingly threatened by anthropogenic impacts. Moreton Bay, a large embayment in south-east Queensland, lies adjacent to one of the fastest growing regions in Australia and has a resident population of bottlenose dolphins, Tursiops aduncus. Evaluation of the effectiveness of any proposed management strategy requires robust population abundance estimates. We estimated abundances of bottlenose dolphins in central eastern Moreton Bay (350 km2) using two commonly used abundance estimation methods for cetaceans: photo-identification mark–recapture and line-transect surveys. Mark–recapture data were analysed in CAPTURE using a model that allowed capture probabilities to vary between sampling events and between individuals. Based on an estimated 76% of the population identifiable photographically, total abundance estimates were 673 ± 130 s.e. (1997) and 818 ± 152 s.e. (1998). Line-transect data, analysed using DISTANCE, gave an abundance estimate of 407 ± 113.5 s.e. (2000). These abundance estimates are large compared with many other coastal bottlenose dolphin populations. The line-transect surveys comprised a pilot study, and the lower line-transect abundance estimate is probably best attributable to methodological issues. In particular, smaller mean group size was estimated for the line-transects surveys (2.85 ± 0.29 s.e.) than the mark–recapture surveys (4.87 ± 0.39 s.e., 1997; 5.78 ± 0.73 s.e., 1998), and line-transect group sizes were probably underestimated. In addition, the line-transect detection probability (g(o)) was assumed to be one but was almost certainly less than one. However, the possibility of an actual decline in population size cannot be ruled out. Coefficients of variation (CV) were lower for mark–recapture than for line-transect surveys, however, CVs of line-transect estimates could be lowered through improved survey design. We evaluated the power of these surveys to detect trends in potential population declines for bottlenose dolphins in Moreton Bay and make recommendations for ongoing monitoring strategies.


Acknowledgments

We would like to thank Helene Marsh, Peter Corkeron, Ivan Lawler and four anonymous reviewers for providing comments and advice that improved this manuscript. Funding for this research came from the Earthwatch Institute and the Australian Research Council. Thanks to Grant Shearwin for being an excellent skipper and dolphin spotter, and to Earthwatch Institute volunteers for field assistance. Research was conducted in accordance with James Cook University animal ethics permits A848 and A517.


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