Daylight occurrence of humpback dolphins Sousa chinensis in Algoa Bay, South Africa

This paper describes the pattern of daylight occurrence of humpback dolphin s Sousa chinensis in Algoa Bay, the Eastern Cape, South Africa, between May 1991 and May 1994. Two indices, the Sighting Index (SI) and the Total Reco rded Dolphin Presence (TRDP), were used to quantify the dolphins' daylight occurrence. Humpback dolphins display a clear pattern of daylight occurrenc e in Algoa Bay and can be seen mostly in the morning, and, to a lesser exte nt, in the evening. This pattern varies little between seasons (with possib le exception for the evening hours), follows the time of the solar day, is not related to the tidal cycle and is probably governed by the diurnal cycl es of dolphins' prey.