Abundance and demography of bottlenose dolphins in Dusky Sound, New Zealand, inferred from dorsal fin photographs

Abstract

The bottlenose dolphins (Tursiops truncatus) of Dusky Sound, Fiordland, New Zealand are a little-studied group at the southern limit of the species range. Conducting a photo-identification census and capture-recapture analyses, we estimated there were 102 (CV = 0.9%) bottlenose dolphins in Dusky Sound during summer 2007/08, the first abundance estimate for this population. We did not encounter individuals from Doubtful Sound in Dusky Sound, suggesting little or no interchange between these neighbouring populations. Using a sex-prediction model derived from laser-metric photographs of dolphins in Doubtful Sound, we predicted the sexes of 79 individuals (98-99% of adults and sub-adults) in Dusky Sound. Our predictions provided a sex ratio of 35 males to 44 females, not significantly different to a 1:1 ratio (G = 1.02, P > 0.05). High resighting rates of individual dolphins suggest the population may be resident, with dolphins observed throughout the entire fiord system. © The Royal Society of New Zealand 2008.