Distribution and habitat partitioning by small odontocetes in the Gully, a submarine canyon on the Scotian Shelf

Abstract

In this paper we examine the summer distribution of three species of small odontocetes in the highly productive waters in and near the Gully, a submarine canyon on the edge of the Scotian Shelf. Atlantic white-sided dolphins (Lagenorhynchus acutus) and common dolphins (Delphinus delphis) were not randomly distributed with respect to depth, sea-floor relief, month of sighting, or sea-surface temperature. Long-finned pilot whales (Globicephala melas) were not randomly distributed with respect to month or sea-surface temperature. These species used the Gully slightly differently, although there was overlap. White-sided dolphins were seen only in the core of the canyon, but were sighted at all temperatures, depths, and sea-floor reliefs and throughout the summer field season. Common dolphins had a modest range throughout the deeper waters and were not seen in the summer before July, when the water warms. Pilot whales ranged widely over the study area, preferring areas with fairly flat relief and were more common later in the summer, when the waters were warmer. It appears that white-sided and common dolphins partition the Gully temporally but not geographically.