Fine-scale habitat selection by coastal bottlenose dolphins: application of a new land-based video-montage technique

Cetacean distribution and underwater topography are frequently correlated. These patterns are commonly studied on large spatial scales, over tens of kilometres, but very rarely on a fine scale. Sightings of bottlenose dolphins, Tursiops truncatus, within the Moray Firth, Scotland, were previously found to be concentrated within deep, narrow channels. To understand why such areas were selected, more-detailed information on the distribution of dolphins was required. This study describes the development of a video technique to study the spatial distribution and relative abundance of bottlenose dolphins. We then used the methodology to investigate whether water depth and seabed gradient influence the dolphins' distribution patterns. Furthermore, temporal patterns of use were examined with respect to seasonal, tidal, and diurnal cycles. The distribution of dolphins was significantly related to topography: dolphins were sighted most frequently in the deepest regions with the steepest seabed gradients. There was a clear temporal pattern in the use of the area, with sightings peaking during July. However, the presence of dolphins was not significantly related to tidal or diurnal cycles. The topography of the area appears to be a significant influence on its intensive use by dolphins, and patterns of use indicate that topography may facilitate foraging during seasonal migrations of fish.