Habitat use and preferences of Indo-Pacific humpback dolphins Sousa chinensis in Algoa Bay, South Africa

This paper examines environmental and behavioral determinants of the habita t use and preferences of Indo-Pacific humpback dolphins inhabiting the Algo a Bay region on the south Eastern Cape coast of South Africa. In order to q uantify the habitat use and preference, two indices were used, the Coeffici ent of Area Use (AU) and the Activity Index (AI). The dolphins inhabit a na rrow strip of shallow, inshore waters of Algoa Bay and remain mostly within 400 m of the shore, in water less than 15 m deep, with no apparent prefere nce for clear or turbid water Water depth is probably the main factor limit ing their inshore distribution, and the 25-m isobath seems to represent the critical depth. Within this confined, inshore distribution, dolphin activi ties concentrate in the vicinity of rocky reefs-their primary feeding groun ds. Dolphin dependence on these shallow-water habitats is evident throughou t the year and, consequently, the inshore shallow reefs are identified as t he "key habitat" which is of primary importance for humpback dolphins in Ea stern Cape waters. The dolphins' dependence on this restricted type of habi tat within an already restricted inshore distribution makes them particular ly vulnerable to alteration or loss of this habitat.