Occurrence ofIndo-Pacificbottlenose dolphins (Tursiops aduncus) off the Wild Coast of South Africa using photographic identification

The present study represents the first reported boat-based photographic identification study of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off the Wild Coast of southeast South Africa. This area is known for the annual sardine run, which attracts apex predators to the region during the austral winter. Dedicated photo-identification surveys were conducted along this coast at three different study sites in February, June, and November of each year from 2014 to 2016. During 47 surveys, 136 bottlenose dolphin groups were encountered, an estimated 4,474 dolphins observed, and 2,149 individuals were identified. Although most individuals (N= 1,770, 82.4%) were only observed once, some were resighted 2-7 times (N= 379, 17.6%), with an average of 305 days (range: 88-705 days) between resightings. The majority of bottlenose dolphins were resighted within the same study site (N= 192), indicating some degree of residency. However, 65 individuals were observed at two different study sites, indicating individual movements along the coast. Our findings contrast earlier suggestions that bottlenose dolphins only use the Wild Coast during the sardine run, as we found large number of animals year-round with some level of site fidelity. This highlights the importance of the Wild Coast to bottlenose dolphins and provides further information on their status off southeastern South Africa.

Automated summary

This study is the first reported boat-based photographic identification study of Indo-Pacific bottlenose dolphins off the Wild Coast of southeast South Africa, revealing the residency and individual movements of these dolphins in the area.