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

Population Sizes and Trends

Commercial whaling had severely depleted all populations of bowhead whales by the 1900s. Whaling started near Labrador in the 1500s and had spread to the Bering Sea by the mid-1800s (Braham 1984). Woodby and Botkin (1993) estimated that there were 10 400-23 000 bowheads in the Bering-Chukchi-Beaufort population prior to whaling and that this number had fallen to less than 3 000 by the time commercial whaling stopped. The commercial whaling period for the Bering-Chukchi-Beaufort Seas population lasted from 1848-1914, with about 20 070 bowheads landed (Ross 1993). Woodby and Botkin (1993) estimated that the Hudson Bay-Foxe Basin population numbered 440 to 470 in 1859 based on catch data from northwestern Hudson Bay between 1860-1915, during which time about 565 bowheads are estimated to have been landed (Ross 1993). Woodby and Botkin (1993) estimated that the Davis Strait-Baffin Bay population numbered 11 000 in 1825, with about 28 695 bowheads landed from 1719-1915 (Ross 1993).


Bering-Chukchi-Beaufort Population

Several methods have been used to estimate the population size of the Bering-Chukchi-Beaufort population (summarized in Zeh et al. 1993). The most recent published estimate, based on the 2001 ice-based census, is 10 470 (95% CI 8 100-13 500 (George et al. 2004). The estimated annual rate of increase from 1978-2001 was 3.4% (95% CI 1.7-5.0%) (George et al. 2004).


Hudson Bay-Foxe Basin Population

Aerial surveys flown on two days in August of 1994 in northern Foxe Basin estimated 256±31.3 and 284 ±48.6 whales (Cosens et al. 1997b). The average of these estimates was 270 bowheads (95% CI 210 - 331) (Cosens et al. 1998; DFO 1999). An estimate of 75 (95% CI 17-133) whales was calculated from an aerial survey of bowheads in northwestern Hudson Bay in August 1995 (Cosens and Innes 2000). These estimates were not adjusted to account for animals that were submerged or otherwise missed by the observers aboard the aircraft. Therefore they are negatively biased. DFO (1999) have used the combined central estimates from the two surveys--345 bowheads--as a minimum estimate of population size (DFO 1999).

The most recent summer surveys (2002-2004) provide the most comprehensive coverage to date of the bowhead whale distribution in the eastern arctic (Cosens et al. 2005). However, the large size of the summer range precluded surveying all areas in one season. In 2002, bowheads were surveyed in Eclipse Sound, Prince Regent Inlet and Gulf of Boothia. In 2003, two concurrent surveys were conducted: southern Gulf of Boothia-Foxe Basin-Hudson Bay and Admiralty Inlet-east coast of Baffin Island. In 2004, surveys were repeated in Admiralty Inlet and Eclipse Sound, and in Barrow Strait.

The total size of the Hudson Bay- Foxe Basin bowhead whale population cannot be estimated because an unknown number of individuals from this population were in Prince Regent Inlet (and thus outside the study area) during the 2003 survey. The best partial estimate for the Hudson Bay-Foxe Basin population in 2003 was 1026 individuals (95% CI = 338-3124) (DFO 2005, Cosens et al. 2005). The confidence limit is extremely wide, indicating considerable uncertainty in the estimate. A total estimate would need to include the unknown proportion of the whales from this population that were summering in Prince Regent Inlet.

The 2003 population estimate was corrected for numbers of whales that were underwater when counts were made. A mean adjustment factor of 3.8 (95% CI = 3.6-4.0) was applied to the survey counts (i.e., number of whales present was 3.8 times more than the number seen) based on the diving behaviour of 4 whales (DFO 2005, Dueck et al. 2005). An important shortcoming, apart from the small numbers of tracked whales, is that the correction factor incorrectly only considers the fraction of time animals are at the surface, and does not consider the window of time that an aircraft would be able to see a whale at the surface (Barlow pers. comm. 2005). The 2003 estimates of abundance are thus biased, and may overestimate population size by 20% (Cooper pers. comm. 2005).

Assuming a total population of 800 (i.e.,1000 reduced by 20% to account for the potential bias) of which 59% are immature, there may be as few as 300 mature individuals and only about 150 mature females. However, amore precautionary approach in view of the uncertainties summarized above is to apply the lower confidence limit of the estimate (i.e., 338), which suggests the current population is significantly lower than pre-exploitation levels (i.e., there may in fact be no more than 50 mature females).

Insufficient quantitative data are available to assess trends for this population. The Inuit Bowhead Knowledge Study (NWMB 2000) reports that elders and hunters from Hall Beach and Igloolik have seen more whales in the 1990s than they did during the 1960s. Similarly, Repulse Bay and Coral Harbour residents report that they saw more bowheads in the 1990s than they did in the 1970s.


Davis Strait-Baffin Bay Population

On the basis of extensive aerial surveys of NW Baffin Bay and Lancaster Sound (conducted between 1974 and 1979), Davis and Koski (1980) estimated that the number of bowheads migrating southward past Cape Adair was 140 ±33. With the rediscovery of the Isabella Bay whales, and a better understanding of population segregation and migrations, Finley (1990) estimated the Baffin Bay population at about 250. Using Finley’s photo-identification data, it was estimated that about 214 whales were present over a two-year period at Isabella Bay (1986-87) and that the total population could number at least 350 (Zeh et al. 1993), or 375 (95% CI 315 - 435) with the inclusion of the northern component of 140±33 (Cosens et al. 1998). The estimate of 375 was considered negatively biased because no adjustment was made to account for submerged whales or whales missed by the observers for the northern component and not all of the whales photographed were included in the mark-recapture estimate for Isabella Bay. In the winter of 1998 Heide-Jørgensen and Acquarone (2002) estimated that 246 bowheads (95% CI 62 - 978) were present off West Greenland between Qeqertarsuaq (lat 69°N 00’) and Paamiut (lat 62°N 00’) and to as far west as 80 km from the coast. This number included an adjustment to account for submerged whales but the survey area did not cover the entire winter range of the population.

A comprehensive estimate of the Davis Strait- Baffin Bay population is not available for 2003 because an unknown number of individuals from this population were already in Prince Regent Inlet, where both Foxe Basin and Baffin Bay whales summered during the 2003 Admiralty Inlet-Baffin Bay survey. The best partial estimate for the Davis Strait-Baffin Bay population is 1539 individuals (95% CI = 631-3770) if the correction factor including cows with calves is used (3.8; time-at-surface=26% of time) and 1944 individuals (95% CI = 797-4762) if the correction factor does not include the data from cows with calves (4.8; time-at-surface=21% of time) (DFO 2005, Cosens et al. 2005). However, the probability of detecting a whale on the aerial survey trackline was incorrectly calculated, and over-inflates the estimate of abundance (Barlow et al. 1988, Laake et al. 1997, Barlow pers. comm. 2005) by perhaps 20% (Cooper pers. com. 2005). The total size of the Davis Strait-Baffin Bay population is unknown, and could only be obtained if the proportion of the population that summers in Prince Regent Inlet were known.

Bowhead whale surveys were conducted in 2004 in Barrow Strait, Admiralty Inlet and Eclipse Sound. However, bowhead whales were seen only in Eclipse Sound (Cleator pers. comm. 2005). Further work is needed to determine if the animals seen were juveniles or adults. Several factors could explain the absence of whales in other areas including weather conditions, presence of killer whale, or ice (DFO 2005, Cosens et al. 2005).

Insufficient quantitative data are available to assess trends for the Davis Strait-Baffin Bay population. Greenlanders reported that the population had not noticeably increased in the last few decades (Reeves and Heide-Jørgensen 1996), but Inuit hunters from Baffin Island reported that numbers there had increased (NWMB 2000). Reeves and Heide-Jørgensen (1996) stated that if this population was increasing in size, it appeared to be doing so mainly in the western part of its range. Aerial surveys continue to be undertaken by DFO to estimate numbers of bowheads in Baffin Bay/Davis Strait, so better estimates of bowhead numbers may be available in future years.

The best partial estimate for the combined eastern Canadian arctic bowhead populations is 5016 (95% CI = 2611-9633) (i.e., Davis Strait-Baffin Bay population and Hudson Bay- Foxe Basin population combined) (DFO 2005, Cosens et al. 2005). This estimate is derived from the pooled 2002 surveys in Eclipse Sound, Prince Regent Inlet and Gulf of Boothia--and is likely overestimated due to the error in calculating the applied correction factor (Barlow pers. com. 2005). A single estimate of all bowheads in the eastern Canadian arctic is unavailable because no single survey covered the entire summer range in one year. The combined estimate is much larger than the totalled partial estimates of the Davis Strait-Baffin Bay and Hudson Bay–Foxe Basin populations. This difference is largely due to the numbers of whales seen during summer in Prince Regent Inlet, which cannot be partitioned between the two populations.

The best available census data suggest that the current population size numbers less than 50% of historic numbers (i.e., pre-commercial whaling). The 2003 partial population estimates indicate that there may be between 1539 (95% CI = 631- 3770) and 1944 individuals (95% CI = 797 - 4762). Even the most optimistic population estimate for all of the eastern Canadian Arctic is less than 50% of pre-exploitation numbers (i.e., 5016: 95% CI = 2611-9633 for Davis Strait-Baffin Bay population and Hudson Bay population). This suggests a population that could number fewer than 3000 individuals of all ages (i.e., 3000 ≈ [5000 – 1000 HBFB pop. est.] X 0.80 bias correction).