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Use of the Robust Design model to estimate abundance and demographic parameters for a coastal bottlenose dolphin (Tursiops aduncus) population

Smith, H., Pollock, K., Waples, K., Bradley, S. and Bejder, L. (2011) Use of the Robust Design model to estimate abundance and demographic parameters for a coastal bottlenose dolphin (Tursiops aduncus) population. In: 48th Annual Conference of the Australian Marine Science Association, 3 - 7 July, Fremantle, Western Australia.


As delphinid populations become increasingly under threat we rely on our capacity to produce accurate estimates of abundance and distribution with which to make management decisions. Many studies have favoured population models where the underlying model assumptions of population closure may be violated due to the movements and biology of the species. This study applied the Robust Design and used photo-identification as a capture-recapture method for estimating abundance, demographic parameters and temporary emigration of an Indo-Pacific bottlenose dolphin (Tursiops aduncus) population between 2007 and 2009. Surveys were conducted along pre-determined transect lines over a 120 km2 study area and occurred year-round through all austral seasons. The model with Markovian temporary emigration was favoured with all other parameters (survival, capture probability and emigration time) varying. Abundance estimates varied seasonally with a low of 65 (± SE 8.53, 95% CI: 54 to 90) in winter 2007 and a high of 139 (± SE 3.41, 95% CI: 134 to148) in autumn 2009. The overall survival estimate was 0.985 (± SE 0.006, 95% CI: 0.964 to 0.994). The abundance estimates provide a baseline for monitoring this population and should be used to parameterise future population viability analyses. These methods set a precedent for abundance estimation of dolphins using a systematic approach with intensive and consistent survey effort year round. The findings show that temporary emigration of individual dolphins from an area can result in different estimates of dolphin abundance seasonally. These modelling techniques could be applicable to population studies of coastal delphinids elsewhere. Given the current rate of coastal development in Western Australia this approach is highly relevant to Environmental Impact Assessment for evaluating impacts on coastal dolphin populations.

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