Fine-scale aspects of habitat use and behaviour by bottlenose dolphins (Tursiops truncatus)
This study explored habitat use and behaviour in a population of bottlenose dolphins (Tursiops truncatus) within the Moray Firth, Scotland between 1997 and 1999. The spatial patterns of use and the surface and diving behaviour of dolphins were studied with respect to key habitat variables in an intensively used region within the populations range. This is a relatively small, coastal channel that is topographically variable in relation to surrounding waters. The study describes the development and application of a land-based technique to study the fine-scale spatial distribution of dolphins and showed that their distribution was significantly related to water depth and the gradient of the seabed; dolphins were sighted most frequently in the deepest regions with the steepest seabed slopes. There was a clear monthly pattern in the use of the area between May and September with sighting frequency peaking during July. The presence of dolphins was not, however, significantly related to tidal or diurnal cycles. Using passive acoustic localisation techniques, the diving behaviour of dolphins was studied and showed that, within the deepest regions of the study area, dolphins used the full water column and consistently dived to depths of around 50 metres, close to the seabed. However the majority of their time appeared to be spent within the surface layers of the water column. In addition, by localising calls that have been associated with feeding (Janik, 2000), it appeared that certain forms of feeding behaviour occurred primarily at depths of between 30 and 40 metres.