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Decline in relative abundance of bottlenose dolphins exposed to long-term disturbance

Bejder, L., Whitehead, H., Samuels, A., Mann, J., Connor, R., Gales, N., Heithaus, M.R., Watson-Capps, J. and Flaherty, C. (2006) Decline in relative abundance of bottlenose dolphins exposed to long-term disturbance. In: 2nd National Wildlife Tourism Conference 2006, 13 - 15 August, Fremantle.


Studies evaluating effects of human activity on wildlife typically emphasize short-term behavioral responses, from which it is difficult to infer biological significance or formulate plans to mitigate harmful impacts. Based on decades of detailed behavioral records, we evaluated long-term impacts of tourist and research vessel activity on bottlenose dolphins in Shark Bay, Australia. We compared relative dolphin abundance within adjacent 36km sites (Tourism site: tourism + intensive research; Control site: periodic research), over three consecutive 4.5-year periods wherein research activity was relatively constant but tourism levels increased from zero, to one, to two dolphin watch operators. A non-linear logistic model demonstrated that, when comparing periods of no-tourism and one-operator within the tourism site, there was no change in dolphin numbers per km; however, as tour operators increased to two, there was a significant average decline of 14.9% (95%CI = -20.8 to -8.23) in dolphin abundance per km (Figure 1), approximating a decline of one per seven individuals. Concurrently, within the control site, there was a non-significant average increase of 8.5% (95%CI = -4.0 to +16.7) in dolphins per km. Given the greater presence, size and noise of tour vessels, tour vessel activity was likely to be the more significant contributor to the decline in numbers of individual dolphins within the tourism site.
Although this trend may not jeopardize the large and genetically diverse Shark Bay dolphin population, the decline is unlikely to be sustainable for local dolphin tourism. A similar decline would be devastating for small, closed, resident and/or endangered cetacean populations. Given the substantial effect of tour vessels on dolphin numbers in a region of low-level tourism, and the overall scarcity of studies with adequate controls or longevity to evaluate this human activity, we urge managers to draw strong inference from the best-studied populations wherein long-term, individually-specific information is available.

Item Type: Conference Item
Murdoch Affiliation(s): Centre for Fish and Fisheries Research
Notes: Conference abstract
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