Habitats important to blue whales (Balaenoptera musculus) in the western North Atlantic
By Lesage, V., Gosselin, J.-F., Lawson, J.W., McQuinn, I., Moors-Murphy, H., Plourde, S., Sears, R., and Simard, Y.
Blue whales (Balaenoptera musculus) in the northwest Atlantic are considered endangered under the Species at Risk Act. Lack of data precluded the identification of critical habitat in the Recovery Strategy published in 2010, which instead included a schedule of studies that, when completed, would allow critical habitat to be identified. After five years of intensive studies, we provide here a review of the available information and current state of knowledge regarding habitats important for Northwest Atlantic blue whales. This information comes from: 1) whaling catch records, 2) photo-identification studies, 3) land, aerial and ship-board surveys, 4) passive acoustic monitoring, 5) satellite and radio telemetry, 6) ice entrapment reports, 7) opportunistic sighting reports, and 8) species distribution modelling.
Blue whales feed while in Canadian waters and their distribution is linked to aggregations of krill. Prey depth strongly interplays with prey density and biomasses in defining habitat quality and bioenergetics of foraging. Arctic krill (Thysanoessa spp.) and northern krill (Meganyctiphanes norvegica) are their two main prey, but the species consumed likely varies seasonally, spatially and among individuals. As a result, habitats important for blue whales were identified using information on blue whale distribution in combination with that of areas of krill aggregations (either observed or predicted). Using the bounding box approach, four areas were identified as important foraging/feeding and socializing areas for blue whales: the lower St. Lawrence Estuary and northwestern Gulf of St. Lawrence, the shelf waters south and southwest of Newfoundland, the Mecatina Trough area, including the head of the Esquiman Channel, and the continental shelf edge of Nova Scotia, Newfoundland and the Grand Banks. Two areas were identified as transit corridors: the Honguedo and Cabot Strait. Wintering areas of blue whales appear relatively diffuse, and include the Gulf of St. Lawrence, southwest Newfoundland, and Scotian Shelf, as well as the mid-Atlantic Bight off the U.S. coast, and warm and deep oceanic waters off this area. Whether breeding occurs in this latter region is unknown. Important features and attributes of important habitats to blue whales include sufficient quantity and quality of prey, free access to transit corridors, enough physical space to freely maneuver, water of sufficient quality to not result in loss of function, and an acoustic environment that does not interfere with communication, passive detection of prey or navigation, or impede use of important habitats by blue whales or their prey. Anthropogenic activities that are likely to result in the loss of functions of these important habitats include those that would result in reduced prey availability or accessibility, acoustic disturbance, environmental contamination, and physical disturbance. It is unclear whether the important habitats identified in this report are sufficient to insure the survival of the Northwest Atlantic blue whales and to meet population recovery goals outlined in the Recovery Strategy. There is a need to expand research efforts outside of the summer period, and to offshore waters and other areas where blue whale sightings are limited but where significant krill aggregations suggest they may be important to blue whales.