Distribution and habitat use of Indo-Pacific bottlenose dolphins Tursiops aduncus along the south coast of South Africa

Abstract

The distribution and habitat use of the Indo-Pacific bottlenose dolphin  Tursiops aduncus along the south coast of South Africa was investigated using bi-monthly boat-based surveys, from 2013 to 2016, over a distance of 145 km between the Goukamma and Tsitsikamma marine protected areas (MPAs). Survey effort totalled 6 239 km and 750.6 hours. Encounters occurred throughout the area (n = 200) and more frequently during winter. Pod sizes ranged from 1 to 350 animals (mean = 45), with calves mostly associated with larger groups. During 70% of the encounters, at least a single calf was present (up to 80 calves; mean = 5) and calves were more prevalent during summer. Encounters occurred mostly in shallower (mean = 11.3 m) and warmer (mean = 17.4 °C) waters. Groups aggregated in larger sizes in colder waters. Most encounters were in Plettenberg Bay and the Goukamma MPA, both of which are characterised by sandy bottoms and sheltered areas. Encounter rates were lowest in rocky and exposed areas, but dolphin groups in such locations were larger and usually travelling. There was a relatively low association of T. aduncus groups with MPAs, except for a sandy area in the Goukamma MPA in particular, suggesting some mismatch between favourable T. aduncus habitat and habitat protection.

Keywords: conservation, generalised linear mixed-effects models,  Goukamma, habitat preference, line-transect survey, marine protected area, Plettenberg Bay, Tsitsikamma, western Indian Ocean