Abundance and population trend (1978-2001) of western Arctic bowhead whales surveyed near Barrow, Alaska

The 2001 survey of western Arctic (Bering, Chukchi, and Beaufort seas) bowhead whales was conducted from 5 April to 7 June near Barrow, Alaska. Visual observers recorded a total of 3,295 new (not seen before) and 532 conditional (possibly seen before) whales in 1,130 h of watch effort, including 121 new calves (3.7% of the new whales). Concurrent with the visual survey, passive acoustic surveillance was conducted almost continuously from 16 April to 31 May, resulting in 27,023 locations of vocalizing bowhead whales. The estimated number of whales within 4 km of the perch (N-4) was 9,025 (SE = 1,068). The estimated proportion of the whales within 4 km of the perch (P-4) was 0.862 (SE = 0.044, computed by a moving blocks bootstrap). Combining these, the abundance estimate (N-4/P-4) for 2001. is 10,470 (SE = 1,351) with a 95% confidence interval of 8,100-13,500. The estimated annual rate of increase (ROI) of the population from 1978 to 2001 is 3.4% (95% CI 1.79%-5%). Reports from hunters and results of an aerial survey in June 2001 indicate whales continued to pass Barrow after the survey had ended. In 2001 51% (572 h) of the watch was scored as occurring during fair-excellent visibility conditions, somewhat lower than the average for all surveys since 1978. Sea ice in the leads and fog were the principle environmental factors affecting visibility for all years. The estimated rate of increase and the fact that the number of calves counted in 2001 is the highest ever recorded suggest a steady recovery of this population. Other populations of large balaenids, notably the North Atlantic right whale, have failed to recover despite 70 yr of protection. The recovery of the bowhead whale is likely attributable to low anthropogenic mortality, a relatively pristine habitat, and a well-managed subsistence hunt. Nonetheless, offshore oil development, increasing shipping traffic, changes in the Bering Sea ecosystem, sea ice retreat, and possibly killer whale predation within its range could impact this bowhead population and should be carefully monitored.