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

Data on the daylight behaviour of humpback dolphins Sousa chinensis were co llected during sea- and land-based surveys undertaken in Algoa Bay, Eastern Cape, South Africa, throughout a three year period. Dolphin activities/beh aviour were categorised as: "feeding", "travelling", "opportunistic feeding ", "socialising and playing", "resting" and "other". It seems apparent that behaviour determines the spatial geometry of the dolphin group, but not th e group size. The surfacing-breathing interval is similar for "feeding", "o pportunistic feeding", and slow "travelling", but differs considerably from the pattern displayed during fast "travelling". Daylight behaviour of hump back dolphins is dominated by "feeding" and shows a regular pattern which i s probably governed by the diurnal cycles of their prey. Generally, "feedin g" peaks in the morning and gradually decreases through the rest of the day . As "feeding" decreases, "travelling" and "opportunistic feeding" increase , both peaking in the afternoon. "Resting" and "socialising and playing" oc cur with similar frequency throughout the day. This pattern varies little b etween summer and winter, as does the overall proportion of daylight behavi ours. The only significant seasonal difference is in the frequency of "soci al/sexual" behaviour which peaks in summer. Although tidal cycle influences to some extent the behaviour of humpback dolphins, in Algoa Bay their dayl ight activity/behaviour is predominantly governed by time of day.