Bowhead whale

Abstract: Tissue δ13C of bowhead whale, Balaena mysticetus, varies seasonally in response to geographic variations in the δ13C of prey organisms consumed along the annual migratory route between the Bering, Chukchi and Beaufort Seas. Seasonal changes in body δ13C of whales taken in 1986 from Alaskan waters provide a means of estimating energy intake from the different habitats in which the whales feed. Adult bowheads do not show significant seasonal shifts in the δ13C of muscle and visceral fat. Their enrichment in 13C relative to subadult whales suggests that they acquire most of their food from fall and winter feeding or from unsampled parts of the summer range where zooplankton are enriched in 13C. Young individuals however, undergo marked seasonal shifts indicating that they feed heavily both in the summer and autumn or winter. Oscillations in δ13C along the length of the baleen also provide a measure of age. Baleen growth rates decline as the whales age and provide a means of correcting for wear loss and allow aging of individuals less than ∼ 12 yr old. Although body length is a poor indicator of age in young bowhead whales, baleen length is closely correlated. Growth rates of bowheads after Year 1 are slow (∼ 0.4m yr-1) and up to 20 yr are required to reach the assumed length of sexual maturity at 13 to 14m.

Abstract: General description: Bowheads belong to a group of whales called mysticetes, which are whales that have baleen instead of teeth. The toothed whales belong to a group called odontocetes. Bowheads are large, rotund whales that are much less streamlined than most other baleen whales. Bowheads can reach 60 ft (18.3 m) and weigh more than 120,000 pounds (54,500 kg). Adaptations for living in arctic and subarctic waters include very thick blubber, up to 1.5 feet (0.5 m), which is used for insulation, energy storage, and padding. Paired blowholes, characteristic of mysticetes, are located at the peak of their large head and they use their blubber padded skulls for breaking ice. The elevated position of the blowholes allows them to breath in small holes in the ice. Bowheads have the largest mouth and head in the animal kingdom and it takes up about one-third of their body length. The upper jaw is arched upward forming the bow-shaped head that distinguishes bowheads from other whales and gives them their name. Bowheads have short, wide flippers and their flukes are very broad, equaling one-third of the body length.

Abstract: 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 (N4) was 7,025 (SE = 1,068). The estimated proportion of the whales within 4 km of the perch (P4) was 0.862 (SE = 0.044, computed by a moving blocks bootstrap). Combining these, the abundance estimate (N4/P4) 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 1.7%-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 howhead 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.

Abstract: The annual migration of bowhead whales ( Balaena mysticetus ) past Barrow, Alaska, has provided subsistence hunting to Inupiat for centuries. Bowheads recurrently feed on aggregations of zooplankton prey near Barrow in autumn. The mechanisms that form these aggregations, and the associations between whales and oceanography, were investigated using field sampling, retrospective analysis, and traditional knowledge interviews. Oceanographic and aerial surveys were conducted near Barrow during August and September in 2005 and 2006. Multiple water masses were observed, and close coupling between water mass type and biological characteristics was noted. Short-term variability in hydrography was associated with changes in wind speed and direction that profoundly affected plankton taxonomic composition. Aggregations of ca. 50–100 bowhead whales were observed in early September of both years at locations consistent with traditional knowledge. Retrospective analyses of records for 1984–2004 also showed that annual aggregations of whales near Barrow were associated with wind speed and direction. Euphausiids and copepods appear to be upwelled onto the Beaufort Sea shelf during Eor SEwinds. A favorable feeding environment is produced when these plankton are retained and concentrated on the shelf by the prevailing westward Beaufort Sea shelf currents that converge with the Alaska Coastal Current flowing to the northeast along the eastern edge of Barrow Canyon.