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To see or not to see: investigating detectability of Ganges River dolphins using a combined visual-acoustic survey

Richman, N.I. and GIbbons, J.M. and Turvey, S.T. and Akamatsu, T. and Ahmed, B. and Mahabub, E. and Smith, B.D. and Jones, J.P.G. (2014) To see or not to see: investigating detectability of Ganges River dolphins using a combined visual-acoustic survey. PLOS ONE, 9 (5). e96811. DOI: 10.1371/journal.pone.0096811

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Abstract

Detection of animals during visual surveys is rarely perfect or constant, and failure to account for imperfect detectability affects the accuracy of abundance estimates. Freshwater cetaceans are among the most threatened group of mammals, and visual surveys are a commonly employed method for estimating population size despite concerns over imperfect and unquantified detectability. We used a combined visual-acoustic survey to estimate detectability of Ganges River dolphins (Platanista gangetica gangetica) in four waterways of southern Bangladesh. The combined visual-acoustic survey resulted in consistently higher detectability than a single observer-team visual survey, thereby improving power to detect trends. Visual detectability was particularly low for dolphins close to meanders where these habitat features temporarily block the view of the preceding river surface. This systematic bias in detectability during visual-only surveys may lead researchers to underestimate the importance of heavily meandering river reaches. Although the benefits of acoustic surveys are increasingly recognised for marine cetaceans, they have not been widely used for monitoring abundance of freshwater cetaceans due to perceived costs and technical skill requirements. We show that acoustic surveys are in fact a relatively cost-effective approach for surveying freshwater cetaceans, once it is acknowledged that methods that do not account for imperfect detectability are of limited value for monitoring.

Item Type: Article
Subjects: Research Publications
Departments: College of Natural Sciences > School of Environment, Natural Resources and Geography
Date Deposited: 09 Dec 2014 16:30
Last Modified: 23 Sep 2015 02:58
ISSN: 1932-6203
URI: http://e.bangor.ac.uk/id/eprint/334
Identification Number: DOI: 10.1371/journal.pone.0096811
Publisher: Public Library of Science (PLOS)
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