Habitat use of a coastal delphinid population investigated using passive acoustic monitoring

The population of bottlenose dolphins in eastern Scotland has undergone significant range expansion since the 1990s, when a Special Area of Conservation was established for the population. Distribution of this population is well described within areas of its range where intensive work has been carried out, such as the inner Moray Firth, St Andrews Bay and the Tay estuary area. However, elsewhere in their range, habitat use is less well understood. In this study, a large-scale and long-term passive acoustic array was used to gain a better understanding of bottlenose dolphin habitat use in eastern Scottish waters, complementing and augmenting existing visual surveys. Data from the array were analysed using a three-stage approach. First, acoustic occupancy results were reported; second, temporal trends were modelled; and third, a spatial-temporal-habitat model of acoustic occupancy was created. Results from the acoustic occupancy are in agreement with visual studies that found that areas near known foraging locations were consistently occupied. Results from the temporal trend analysis were inconclusive. Habitat modelling showed that, throughout their range, bottlenose dolphins are most likely to be detected closer to shore, and at a constant distance from shore, in deeper water.