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COSEWIC Assessment and Update Status Report on the Bowhead Whale in Canada

Habitat

Habitat Requirements

Bowheads occur in marine waters and in conditions ranging from open water to thick, extensive (but unconsolidated) pack ice. They are able to break thick ice (over 20 cm) to breathe and can navigate under extensive ice fields (George et al. 1989). Once bowheads arrive on their summering grounds, their primary activity is feeding (Thomas 1999; Würsig et al. 2001). Thus habitat requirements during this time would depend on the distribution of their primary food source (zooplankton), which can be affected by temperature and salinity, nutrient availability, and light intensity (Mackas et al. 1985). This along with water masses of different properties can influence the distribution and abundance of zooplankton (Simard et al. 1986; Castel and Veiga 1990). Physical processes in the Beaufort Sea vary considerably from year to year, causing the distribution and abundance of zooplankton to also vary (Griffiths and Thomson 2001).

On the summering grounds in July, bowheads from the Bering-Chukchi-Beaufort population seem to aggregate in the western half of Amundsen Gulf in deep areas (>200 m), where breakup occurs early. By late August, they have moved farther west into shallower waters (<100 m) east and west of the Mackenzie Delta (Richardson et al. 1987a). Subadults (<10 m long) are the dominant group in shallow (<20 m) nearshore areas during the fall migration in the Alaskan Beaufort Sea, with progressively fewer small subadult whales and more large subadults and adults as water depth increases (Koski and Miller 2001). Using sighting data from aerial surveys, Moore et al. (2000) found that bowheads selected inner shelf waters (≤50 m) and light ice conditions in the autumn. Moore (2000) also found that bowheads selected shallow inner-shelf waters (≤50 m) during moderate and light ice conditions, and deeper slope habitat (201-2000 m) during heavy ice conditions. Some adults may summer far offshore in pack ice or at the ice edge (Richardson et al. 1987a; Koski pers. comm. 1999).

Bowheads in Foxe Basin aggregate along the land-fast ice edge in June and July before the ice breaks up. The whales use the ice edge for socializing and feeding, possibly because the ice edge offers both food and shelter (Thomas 1999).

In Isabella Bay (east coast of Baffin Island), whales congregate in areas that correspond to major underwater bathymetric features (Finley 1990; Finley et al. 1994). Most feeding activity takes place in two deep troughs where food is most concentrated, and most social-sexual activity takes place on Isabella Bank, possibly because it offers both protection from killer whales and shelter from heavy seas and strong currents (Finley 1990; Finley et al. 1994).


Trends

There is considerable variation among years in the geographic locations where bowheads are sighted during their fall migration (Koski and Miller 2001), and in the summering areas in the Canadian Beaufort Sea (Richardson et al. 1987a; Moore and Reeves 1993). The near absence of bowheads in northern Foxe Basin in August 1999, when they are normally abundant there, raised a number of questions about the distribution patterns of the Hudson Bay-Foxe Basin population (Cosens and Blouw 2003). Koski and Miller (2001) suggested that between-year variation is related to the local abundance of bowhead prey and the differing locations of water mass boundaries that affect zooplankton (Griffiths and Thomson 2001; Griffiths et al. 2001).

Oil development in the Alaskan Beaufort Sea may be causing bowheads to migrate farther offshore. Richardson et al. (1995) observed an avoidance response to active seismic vessels as far as 20 km away. However, the disturbance from oil and gas development is not known to have affected the population growth rate.


Protection/Ownership

Bowhead habitat is potentially protected in Canada by the Fisheries Act, which prohibits the destruction of any fish habitat (Section 32, 27(2) of the Fisheries Act). A marine protected area is being developed for Igaliqtuuq, near Clyde River, through the proposed Igaliqtuuq Bowhead Conservation Plan (Moshenko et al. 2003). The Hudson Bay Oceans Working Group is developing an Integrated Management Plan for Hudson Bay, with the goal of protecting, maintaining and enhancing the health of the Hudson Bay ecosystem (Oceans Canada 2002). Although there is no marine protected area in the Beaufort Sea yet, a harvest-based monitoring program called the Tariuq (Ocean) Monitoring Program is undertaken by local fishermen, and deals with the ecology, management and contaminants of the southern Beaufort Sea (Oceans Canada 2002). Also, the Beaufort Sea and Amundsen Gulf are in the Inuvialuit Settlement Region, and any project that could disturb the habitat there would have to be subjected to screening and possibly public review under the screening and review process of the Inuvialuit Final Agreement. In the Nunavut Settlement Area, projects that could potentially disturb bowhead habitat are initially reviewed by the Nunavut Impact Review Board, which forwards its findings to other organizations such as DFO and NWMB.