Group Movements of White-Beaked Dolphins (Lagenorhynchus albirostris) near Halifax, Canada

Abstract: Movement patterns of animals are important in understanding their role in the environment (e.g., foraging, residency) and may provide insight into an animal’s life history and social structure. Movement is particularly important for animals where resources are highly temporally and spatially variable such as in the marine environment. Groups of white-beaked dolphins (Lagenorhynchus albirostris) were tracked at sea near Halifax, Nova Scotia, Canada, during the early summer months from 2003 to 2005. Twelve groups were followed for 20 min or more, and GPS positions of the research vessel when within approximately 10 m of the dolphins were used to determine group movements. For each group, movements were quantified by determining the straight-line bearing, swim speed, and directional deviation (the degree of deviation from straight-line travel). Spearman’s correlations were calculated between these variables and day, time, mean water depth, bathymetric variability, dolphin group size, and number of young dolphins in the group. Significant negative correlations were found between bathymetric variability and swim speed (rs = 0.839, p = 0.001) and between bathymetric variability and directional deviation (rs = -0.608, p = 0.036). A significant positive relationship was found between directional deviation and mean water depth (rs = 0.755, p = 0.005). This indicates a tendency for dolphin groups to vary their direction of travel more frequently in areas with lower bathymetric variation and deeper water and to increase their swim speed in areas of lower bathymetric variation. A significant positive relationship was also found between group size and swim speed (rs = 0.880, p < 0.001). A possible explanation is that these dolphins are altering their movement patterns and group size in relation to foraging activities.

Key Words: movement, white-beaked dolphin, Lagenorhynchus albirostris, cetacean, depth, bathymetry, group size

Document Type: Research article

DOI: 10.1578/AM.34.3.2008.331

Page Numbers: 331-337

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