Assessing spatial segregation of beluga whales (Delphinapterus leucas) in Western Hudson Bay estuaries

Abstract

Segregation of older adult males from females and immature males is known to occur in some beluga whale populations, but it is unclear if adults accompanied by calves segregate in Hudson Bay, where the largest summering population is found. Using imagery from a photographic aerial survey conducted in August 2015, we considered a number of environmental variables that might explain distribution by age class of beluga near two of three main estuaries (Churchill and Seal River) used by Western Hudson Bay belugas in the summer season. Belugas were identified and classified by age manually using an identification decision tree and GPS coordinates were plotted in ArcGIS. Distribution by age class was examined in relation to distance to coastal habitat and bathymetry to test the predation risk hypothesis, sea surface temperature (thermal advantage hypothesis), and extent of river plume (forge-selection hypothesis). Habitat characteristics and the proportion of age classes in both estuaries were similar between age class groups (with and without calves) indicating no segregation and suggesting the environmental data assessed were not driving patterns of distribution and density of age classes at the spatial and temporal scale being investigated. Results provide a greater understanding of spatial patterns of beluga whale habitat use in western Hudson Bay and information useful in conservation and management advice.