Bioacoustics of Balaena mysticetus

Movements, Home range and Social organization. Seasonal distribution and movements of Bowhead Whales are closely associated with changes in cover of sea ice. They migrate to high Arctic latitudes in summer and return to more marginal ice areas during maximum ice in winter, traveling seasonally between high-productivity areas of densely concentrated prey species. Data from satellite monitoring of nine radio-tagged whales off West Greenland indicated localized use of a single site for 3-6 weeks between long-distance, offshore movements that lasted 1-2 weeks. Travel velocity was up to 200 km/day, which was considered too rapid for foraging to be feasible during these long-distance movements. It has been suggested that Bowhead Whales meet their energetic needs during intense feeding periods; their large body size combined with blubber stores may accommodate the energy needed to survive variability in pelagic productivity and allow for long-distance travel between regions of greater prey availability. Bowhead Whales are generally observed individually or in groups of up to three. Larger groups are observed during migration, and like right whales, Bowhead Whales form large aggregations on feeding grounds. Segregation by sex has been documented in Bowhead Whales. For example, mature females without offspring are thought to occupy Disko Bay, whereas primarily female—offspring pairs are observed in Foxe Basin. Baffin Bay is commonly occupied by adult males and by resting or pregnant females from Disko Bay. Prince Regent, Gulf of Boothia, Foxe Basin, and north-western Hudson Bay, Canada, are used by nursing females, their offspring, and subadults. It has been suggested that mature females (without young) use Disko Bay as a feeding ground during phases of the reproductive cycle. Interestingly, acoustic recordings of singing individuals may indicate that breeding occurs in Disko Bay, and males may be following estrous females into the area. Segregation by size class of Bowhead Whales has been observed in the Central Beaufort Sea, where small subadult individuals occupied shallow nearshore habitats and size class of whales increased with increasing water depth. Timing of movements arriving to and moving through the observed area was also segregated by size. Small subadults arrived first in late August and departed in late September, and adults arrived last in late September. Mother—offspring pairs arrived in early September and were commonly observed until early October.

Status and Conservation. CITES Appendix I. Classified as Least Concern on The [UCN Red List, with the Sea of Okhotsk subpopulation classified as Endangered and the Spitsbergen subpopulation classified as Critically Endangered. The Bowhead Whale traditionally has been divided into five subpopulations, or “putative stocks,” mainly based on geographic discontinuities: Baffin Bay—Davis Strait, Hudson Bay-Foxe Basin, Bering—Chuckchi-Beaufort Seas (BCB), Sea of Okhotsk, and Svalbard-Barents Sea (Spitsbergen). Nevertheless, recent satellite tracking and genetic data have resulted in combining Baffin Bay—Davis Strait and Hudson Bay—Foxe Basin into a single stock, which is now called the Eastern Canada—Western Greenland stock. The Spitsbergen Bowhead Whales are found across the North Atlantic from off eastern Greenland (Denmark) in the Greenland Sea, the Barents Sea, and into the Kara Sea to Severnaya Zemlya (Russia), and south at least occasionally to northern Iceland and the coast of Norway and Jan Mayen (Norway). The stock of Bowhead Whales in the Sea of Okhotsk is restricted to the northern part of this region. During summer, these whales are mainly in waters south of Shantar Island and in spring in the gulfs of Gizhiginskaya and Penzhinskaya; during the winter, they live in polynyas (open water surrounded by ice) in the region. They are rare outside this region, but one stranding is known from Osaka Bay, Japan, in 1969. The largest and best known population of Bowhead Whales occurs in the BCB seas from Chaunskaya Bay (c.69° 21’N, 169° 46’E), Russia, in the western Chukchi Sea east to Amundsen Gulf in Canada, and in the northern Bering Sea south to Karaginskiy Bay near the base of Kamchatka Peninsula (c.59° 33’N, 164° 48°E), St. Matthew Island, Alaska. The newly combined Eastern Canada-Western Greenland population is found in summer in the Hudson Bay-Foxe Basin region in northern Hudson Bay, Hudson Strait, Foxe Channel, and Foxe Basin. In the Baffin Bay-Davis Strait region, Bowhead Whales spend summer in the eastern Canadian Arctic Archipelago and off the east coast of Baffin Island. As ice forms in autumn, they are found in open water near the ice edge off West Greenland and eastern Baffin Island. Summering grounds include Cumberland Sound, and in late summer and autumn, their feeding grounds are in Isabella Bay, Lancaster Sound, Admiralty Inlet, and Eclipse Sound. In recent years, there has been some spatial overlap in the extreme summer ranges of the BCB and Eastern Canada—Western Greenland stocks. In 2006-2010, 58 Bowhead Whales from the BCB stock and West Greenland were tagged and tracked via satellite. Two of them entered the Northwest Passage in the Canadian High Arctic, one from the BCB stock and one from the opposite direction in West Greenland. They spent approximately ten days in the same area, demonstrating that there is at least some seasonal overlap between the two stocks. This overlap is the result of climate change that has opened the Northwest Passage to populations of Bowhead Whales previously separated by sea ice. The global population of Bowhead Whales is estimated at more than 24,000 individuals, with the majority of them found in the BCB stock. All stocks were greatly reduced by commercial whaling starting in 1610 in the eastern North Atlantic Ocean. Bowhead Whales are hunted today by indigenous Russian, Alaskan, Canadian, and Greenland hunters in subsistence fisheries that are closely monitored and have with annual quotas. More recently, the Eastern Canada—Western Greenland stock is also increasing. Nevertheless, status of stocks in the Sea of Okhotsk and Svalbard-Barents Sea (Spitsbergen) in terms of actual numbers and any population growth remain unclear. The BCB stock has been increasing at least since the mid-1970s when a longterm monitoring program began. The BCB stock in spring 2011 was estimated at 16,892 individuals and from the mid-1970s to 2004, the stock increased 3-5% /year. The original BCB stock was estimated at 10,000-20,000 individuals. Therefore, the current stock is well within the range of its historic abundance. This stock is listed as a subpopulation on The IUCN Red List as Least Concern, the same as the overall listing for the species, because the BCB whales make up the majority of the world population of Bowhead Whales. The abundance estimate of the Eastern Canada—Western Greenland subpopulation was 6344 individuals in 2003, but the minimum original size of this stock was estimated at ¢.24,000 individuals. Therefore, the current stock is only c.25% ofits original numbers. This stock has not been assessed for The IUCN Red List. Current size of the subpopulation in the Sea of Okhotsk is poorly known. The only estimate, based on genetic mark-recapture data from 2000, is 247 individuals. During the 1960s,illegal Soviet pelagic whaling operations killed at least 145 Bowhead Whales in the Sea of Okhotsk. Minimum pre-whaling number was estimated to be ¢.3000 individuals. Therefore, at best, the current stock is less than 10% ofits original size. There is no population estimate for the Spitsbergen stock, butit is thought to number under 100 individuals and there is limited evidence that it is increasing. The minimum pre-whaling size of the Spitsbergen stock was ¢.12,000 individuals. For all four subpopulations of Bowhead Whales, the primary potential threat is disturbance from oil and gas activities, which can decrease feeding efficiency. Other threats include bycatch from different types of fishing gear. How the future loss of sea ice due to climate change will affect Bowhead Whales is unknown, but ship strikes will no doubt increase as ship traffic and industrialization increase in their arctic habitat. Ship noise will also increase, and background noise masks calling among Bowhead Whales. As oil and gas activities increase, there is also an increased risk of oil spills. Oil would clearly be destructive to habitats of Bowhead Whales and increase their exposure to contaminants. Spilled oil would also matt their baleen plates, making it impossible for them to filter feed.