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

Distribution

Global Range

Bowheads have a nearly circumpolar distribution in the northern hemisphere, spanning latitudes 54°N – 75°N in the North Pacific basin and 60°N – 85°N in the North Atlantic basin (Moore and Reeves 1993). Several physical barriers (land or impassable sea ice) have been thought to divide the world bowhead population into five populations (Moore and Reeves; Figure 2): (1) Okhotsk Sea population, largely or entirely confined to this sea year-round; (2) Bering-Chukchi-Beaufort Seas population, which summers in the eastern Beaufort Sea and Amundsen Gulf, and winters in the central and eastern Bering Sea; (3) Hudson Bay-Foxe Basin population, assumed to winter mainly in northern Hudson Bay and Hudson Strait, and to summer mainly in Foxe Basin and northwestern Hudson Bay; (4) Davis Strait-Baffin Bay population, which summers in Baffin Bay and the Canadian High Arctic, and winters along the ice edge in Davis Strait and off West Greenland; and (5) Svalbard (Spitsbergen) population, centred in the Barents and Greenland Seas.


Figure 2: Approximate Global Distribution of the Five Bowhead Whale Populations

Figure 2: Approximate global distribution of the five bowhead whale populations(after Braham et al. 1984).

After Braham et al. 1984.

Bowheads were hunted by Inuit in the 1700s along the Labrador coast to as far south as Hopedale (Taylor 1988). They were also a major target, and possibly the principal target, of the very large-scale Basque commercial whale hunt centred in the Strait of Belle Isle during the 1500s and 1600s (Rastogi et al. 2004). No live bowheads have been observed in the southern Labrador Sea for more than a century, but a dead juvenile was found floating off northeastern Newfoundland in October 1998 (Daoust et al. 1998). It is not clear whether the bowhead whales killed in the Strait of Belle Isle and St. Lawrence estuary in the 1500s and 1600s formed a distinct population, or whether they were part of the Davis Strait-Baffin Bay population that ranged further south during the Little Ice Age (Rastogi et al. 2004). Genetic analysis of bones recovered from historic whaling sites is required to resolve this question.

The bowhead’s range is affected over long time scales by sea ice fluctuations (Schledermann 1976; McCartney and Savelle 1985; Dyke and Morris 1990; Dyke et al. 1996). During the climatic optimum (7 500 - 10 000 years ago) bowheads roamed more widely in the Canadian Arctic, with possible mixing between the eastern and western Arctic populations (Bednarski 1990). Some exchange may have occurred in more recent times as well (Bockstoce and Burns 1993).

Of particular relevance to the description of population ranges is the distinction between the Hudson Bay-Foxe Basin and Davis Strait-Baffin Bay populations. Until recently, the evidence supporting the distinction was circumstantial and indirect (Reeves et al. 1983; Reeves and Mitchell 1990). Preliminary genetic evidence of mtDNA haplotype frequencies, presented by Maiers et al. (1999), appear to be corroborative. The most common of 22 haplotypes studied made up the highest proportion in both the Bering-Chukchi-Beaufort (3/9 animals) and Hudson Bay-Foxe Basin (13/34 animals) samples, but this haplotype was not found at all in the Davis Strait (0/19 animals) samples. Maiers et al. (1999) also concluded provisionally that the Hudson Bay-Foxe Basin population was more similar to the Bering-Chukchi-Beaufort than to the Davis Strait-Baffin Bay population.

More recently, molecular genetic analyses (DNA sequencing of the mitochondrial d-loop region and analysis of 15 nuclear DNA microsatellite loci) were completed for 286 individual bowheads sampled at various locations across the eastern Canadian Arctic and west Greenland (Postma et al. 2005, DFO 2005). Nuclear DNA microsatellite results showed genetic differentiation among some of the sample groups, specifically the samples from Igloolik in northern Foxe Basin as compared to those from West Greenland and from Pangnirtung in southeastern Baffin Island. Furthermore, the Repulse Bay (Hudson Bay) samples were differentiated from the West Greenland samples, but not from the Pangnirtung samples.

DFO (2005) noted that the recent genetics data could be explained as indicating a complex structure of a single population that is segregated by age and/or sex or selective mating strategies. However, the available genetic analyses indicate that the tissue samples obtained from bowhead whales from the eastern Canadian Arctic came from more than one population (DFO 2005). This is consistent with the earlier genetic evidence and the assumption that there are two populations of bowhead whales in the eastern Canadian arctic-the Hudson Bay-Foxe Basin population and the Davis Strait-Baffin Bay population.


Canadian Range

Bering-Chukchi-Beaufort Population

Bering-Chukchi-Beaufort bowheads winter (November to April) in the western and central Bering Sea where there is adequate open water and broken pack ice. Recent winter sightings have been mainly along the ice edges and in polynyas in the pack ice near St. Matthew and St. Lawrence Islands and in the northern Gulf of Anadyr (Moore and Reeves 1993) (Figures figure3 and figure4). In spring (April through June) the whales migrate north and east to the eastern Beaufort Sea (Figure 3). The spring distribution is restricted to open-water areas that develop as the ice breaks up. The summer (June to September) distribution is primarily in the eastern Beaufort Sea, along the south and west coasts of Banks Island, in Amundsen Gulf, and along western Tuktoyaktuk Peninsula. Sightings in the eastern Chukchi and western Beaufort Seas in June (Braham et al. 1980; Carroll et al. 1987), along the Chukotka Peninsula throughout the summer (Bogoslovskaya et al. 1982), and in the Alaskan Beaufort Sea in August (Moore et al. 1989) indicate that not all animals in this population summer in the eastern Beaufort Sea. In the fall (September and October), bowheads migrate west from the Canadian Beaufort Sea into the Alaskan Beaufort and the Chukchi Sea, and then into the Bering Sea.


Figure 3: Generalized Seasonal Occurrence and Migration Corridor for the Bering-Chukchi-Beaufort Sea Bowhead Population

Figure 3: Generalized seasonal occurrence and migration corridor for the Bering-Chukchi-Beaufort Sea bowhead population.


Figure 4: Map of the Canadian Western Arctic Showing Places Mentioned in Text

Figure 4: Map of the Canadian western arctic showing places mentioned in text showing 1. Amundsen Gulf; 2. Banks Island; 3. Gulf of Anadyr; 4. Hershel Island; 5. Kaktovik; 6. Point Barrow; 7. St. Lawrence Island; 8. St. Matthew Island; 9. Tuktoyaktuk Peninsula.

Showing 1. Amundsen Gulf; 2. Banks Island; 3. Gulf of Anadyr; 4. Hershel Island; 5. Kaktovik; 6. Point Barrow; 7. St. Lawrence Island; 8. St. Matthew Island; 9. Tuktoyaktuk Peninsula

Nineteenth-century commercial whalers took bowheads from spring to autumn in the northern and southwestern Bering Sea (Bockstoce and Burns 1993). Bockstoce and Burns (1993) assumed that these bowheads were on their normal feeding grounds and not migrating through those areas, leading to the speculation that the Bering-Chukchi-Beaufort population consisted of several subpopulations. Bockstoce and Burns (1993) suggested as an alternative hypothesis that the bowheads comprised a single population that responded rapidly to the whaling activities and fled from areas of intense hunting, causing them to recede farther north and east to temporarily safer areas. The issue of whether there was (or is) more than one population in the western Arctic has been the subject of intense debate within the IWC Scientific Committee over the last few years.

The extent of occurrence of the bowheads in western Canadian Arctic waters extends from the Alaskan/Yukon border east into Amundsen Gulf (~900 km) and from the shore out to at least 230 km, with most animals occurring within 100 km of shore (Richardson et al. 1987a). The extent of occurrence of the Bering-Chukchi-Beaufort population in Canadian waters is therefore approximately 200 000 km2 (900 km x 230 km). This extent of occurrence is stable. The area of occupancy of this population in Canadian waters is approximately 90 000 km2 (900 km x 100 km). The area of occupancy obviously fluctuates seasonally, depending on prey distribution and other factors. Annual differences are also linked to variability in prey distribution (Richardson et al. 1987a).

Hudson Bay-Foxe Basin Population

Relatively dense aggregations of bowhead whales occur in summer in northwestern Hudson Bay around Repulse Bay and Frozen Strait, and in northern Foxe Basin, north of Igloolik (Figures figure5 and figure6). Scattered individuals and small groups also occur along the west coast of Hudson Bay and near Mansel and the Ottawa Islands in eastern Hudson Bay (Reeves and Mitchell 1990). Some animals winter in Hudson Strait (ca. 800 km long)and northeastern Hudson Bay (McLaren and Davis 1982).


Figure 5: Generalized Seasonal Occurrence and Migration Corridor for the Hudson Bay-Foxe Basin Population of Bowhead Whales

Figure 5: Generalized seasonal occurrence and migration corridor for the Hudson Bay-Foxe Basin population of bowhead whales.


Figure 6: Map of the Canadian Eastern Arctic Showing Places Mentioned in Text

Figure 6: Map of the Canadian eastern arctic showing places mentioned in text.

Showing: 1. Barrow Strait; 2. Bylot Island; 3. Cape Adair; 4. Cape Hopes Advance; 5. Cumberland Sound; 6. Disco Bay; 7. Fisher Strait; 8. Frozen Strait; 9. Fury and Hecla Strait; 10. Gifford Fiord; 11. IsabellaBay; 12. Jens Munk Island; 13. Kane Basin; 14. Labrador Sea; 15. Lyon Inlet; 16. Mansel Island; 17. Marble Island; 18. North Water; 19. Ottawa Islands; 20. Pond Inlet; 21. Prince Regent Inlet; 22. Repulse Bay; 23. Roes Welcome Sound; 24. Southampton Island

Ross (1974) estimated that the 19th century commercial whaling grounds for bowheads in northwestern Hudson Bay covered an area of 60 000 km2 (23 000 square miles), extending from Marble Island northeastward through Roes Welcome Sound to Lyon Inlet and into Fisher Strait (also see Reeves and Cosens 2003). Much of this area is still used by bowheads (NWMB 2000). Aerial surveys in August 1995 found bowheads in Roes Welcome Sound, Repulse Bay and Frozen Strait (Cosens and Innes (2000). In Foxe Basin, animals congregate in a well-defined area of approximately 3700 km2 north of Igloolik Island. This region extends from Fury and Hecla Strait eastward 71 km to Jens Munk Island, and from Igloolik Island northward 52 km to Gifford Fiord. Recent satellite tracking has shown that bowheads also move through Fury and Hecla Strait and into the Gulf of Boothia and northward into at least the southern reaches of Prince Regent Inlet (Dueck pers. comm. 2002). Bowheads are observed migrating north along the western side of Foxe Basin, and they have also been seen along the eastern side of Foxe Basin during the spring (NWMB 2000).

The extent of occurrence of the Hudson Bay-Foxe Basin population is approximately 350 000 km2 (Appendix 1, Table 1). This extent of occurrence is considered stable. The area of occupancy of the Hudson Bay-Foxe Basin population is approximately 250 000 km2 (Appendix 1, Table1).

The fine-scale distribution of bowheads is probably influenced by the movements of killer whales and the availability of invertebrate prey species. In August 1999 bowheads were nearly absent in their usual northern Foxe Basin feeding area (Cosens and Blouw 2003). They had arrived there in June 1999, but by August they had moved away. Local people reported unusual behaviour by many marine mammals that summer (Wheatley pers. comm. 2004). Ice breakup patterns differed from “normal,” in part owing to the early passage of an ice-breaker through Frozen Strait; also, killer whales were present in higher numbers than usual (Wheatley pers. comm. 2004).

Davis Strait-Baffin Bay Population

Some of the animals in this population move westward through Lancaster Sound in late June and early July, remaining in the inlets and sounds of the High Arctic until September (Figures figure6 and figure7). Others, mainly adults and adolescents, remain off the east coast of Baffin Island for the summer and autumn (Davis and Koski 1980; Finley 1990), migrating northwards from eastern Baffin Island (NWMB 2000) or across from Greenland (Heide-Jørgensen et al. 2003). Some bowheads winter in and near Disko Bay, West Greenland (Heide-Jørgensen and Finley 1991; Reeves and Heide-Jørgensen 1996), arriving there in late November and December and remaining until April or May (Born and Heide-Jørgensen 1983). Other bowhead whales are believed to winter in central Davis Strait and southern Baffin Bay in the unconsolidated pack ice and in polynyas (Finley 1990, 2001).


Figure 7: Generalized Seasonal Occurrence and Migration Corridor for the Davis Strait-Baffin Bay Population of Bowhead Whales

Figure 7: Generalized seasonal occurrence and migration corridor for the Davis Strait-Baffin Bay population of bowhead whales.

Bowheads attributed to this population occur in Canadian waters from the southern ice edge in Davis Strait north to the North Water in the High Arctic (~2100 km), and from Baffin Island east to the Greenland coast. During the summer months they are also found in Lancaster Sound and Barrow Strait, and in the inlets adjoining them. The extent of occurrence of the Davis Strait-Baffin Bay population in Canadian waters is therefore approximately 800 000 km2 (Appendix 1, Table 2).

The extent of occurrence in the Arctic is considered stable as bowheads occur in many of the same areas where they were found during the period of commercial whaling. However, they are no longer found in the Gulf of St. Lawrence and Strait of Belle Isle where they were hunted by Basque whalers in the 1500s (Rastogi et al. 2004). Whether or not the whales that were killed in this region belonged to a separate population or were part of the Davis Strait-Baffin Bay population is unknown (Rastogi et al. 2004). The current area of occupancy for the Davis Strait-Baffin Bay population is approximately 300 000 km2 (Appendix 1, Table 2).