An activity budget was determined for Pacific bottlenose dolphins (Tursiops truncatus) in a 0.5 km wide by 32 km long study area located in the coastal waters of north San Diego County during daylight hours. Twelve months of cliff-based behaviour sampling accumulated 213 hrs of direct observation on 73 dolphin schools. Behaviour was documented through instantaneous samples of focal group activity taken at 3 min intervals, evenly distributed across time of day and season. The overall proportion of time spent in each of the five behaviour states was: travel (63%), feed (19%), social (12%), play (3%) and rest (3%), and 90% of all dolphin activity occurred within 0.25 km of shore. Dolphin behaviour proportions were relatively constant across seasons except for an increase in social activity during the summer. Feeding time increased during the early morning and late afternoon; during periods of high tide current; and in ocean border, reef, and estuary habitats. Distributions of travel time were inversely related to feeding across diurnal, tide, and habitat type analyses. Variations in the temporal and spatial distribution of feeding were integrated with a review of the trophic relations and availability of 25 dolphin prey fish. Our interpretation of these data placed primary emphasis on seasonal and diurnal temporal cycles, tide currents, and habitat features which affect dolphin prey directly, while secondary emphasis was placed on the coastal distribution of prey species nutrients.
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