Daylight behaviour of dusky dolphins (Lagenorhynchus obscurus) in Golfo Nuevo, Argentina

MARIANA DEGRATI; GRISELDA V. GARAFFO; SILVANA L. DANS; SUSANA N. PEDRAZA; ENRIQUE A. CRESPO

Liege

Congreso; 16th EUROPEAN CETACEAN SOCIETY CONFERENCE; 2002

The dusky dolphin is one of the most commonly occurring cetaceans off Patagonian coasts, Argentina. During the last few years the occasional sighting of dusky dolphins has been discovered as an alternative for other tourism activities in the region, in particular whale-watching. The objective of this study is to describe the general behaviour of dusky dolphin schools in Golfo Nuevo and to analyse the activity budget, that is to say the proportion of time spent in each activity, throughout the daylight hours. This information will be useful at the time of evaluating the potential impact of watching tours. Observations were made from a commercial boat as well as a research boat from January to May, 2001. Once a group of dolphins was sighted, it was considered the focal group and followed as long as possible. Group size and composition were recorded at the time of the sighting. Behaviour and activity were recorded for each 2min intervals thereafter. During each interval, we recorded the number of clean leaps and noisy leaps. At the end of each interval, the predominant activity of the group was assigned as “feeding”, “travelling, “resting”, “socialising” and “milling”. Dusky dolphins were observed for 95hs, and behaviour was specifically recorded for 95 focal groups. The daily activity pattern of dolphins was dominated by “travelling” (46% of the observation time). An increase in the time spent in “travelling” and a decrease in “resting” towards the afternoon was observed although the difference was not statistically significant. Mothers with calves groups were more frequently observed “resting”, while “socialising” only appeared in mixed and adult and juvenile groups. Noise leaps happened in more number when the activity was “socialising”, and they were almost null during  “resting”. Clean leaps were more frequent during “feeding”. Sequences of  “travelling” and “feeding” were detected in which “travelling” periods were longer than “feeding” periods ( =10 and 7 min respectively). Feeding periods lasted longer in larger groups (r=0.525, p<0.0001).