Balaena mysticetus, Linnaeus, 1758

Russell A. Mittermeier & Don E. Wilson, 2014, Balaenidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 186-215 : 212-215

4.

Bowhead Whale

Balaena mysticetus

French: Baleine boréale / German: Gronland-Wal / Spanish: Ballena de Groenlandia

Other common names: Arctic Right Whale, Bowhead, Bunch-back Whale, Great Polar Whale, Greenland Right Whale, Greenland Whale, Steeple-top

Taxonomy. Balaena mysticetus Linnaeus, 1758 ,

“Habitat in Oceano Greenlandico” (= Greenland Sea).

This species is monotypic.

Distribution. Circumpolar in the N Atlantic Ocean (NE Canada-W Greenland and E Greenland, Svalbard, Barents and Kara seas) and N Pacific Ocean (Bering—Chuckchi-Beaufort seas and Sea of Okhotsk).

Descriptive notes. Total length maximum 1800 cm (males) and up to 2000 cm (females); weight can exceed 100,000 kg. Bowhead Whales are massive and frequently described as rotund. Like other mysticetes, Bowhead Whales are sexually dimorphic, with females slightly larger than males. Head is enormous and may compose more that one-third of the total body length. Bowhead Whales have a noticeable postcranial indentation posterior to blowhole at the neck area. Blowhole is pronounced, situated on a prominence composed of dense fibrous connective tissue and muscle. Blowhole openings are widely separated from one another and angle slightly to the sides. Spoutis a V-shaped spray that can be as much as 5 m high. Rostrum is extremely arched, and mouth is strongly bowed. There are 230-360 baleen plates suspended from each side of the upper jaw. Baleen is up to 500 cm in length, the longest of any baleen whale. Plates are dark gray or brown to black and are fringed with long, fine bristles. Eyes are located above gape of mouth. There is no dorsal fin on the broad, smooth back. Flippers are large, and flukes are wide, reaching up to 600 cm across. Bowhead Whales are adapted to ice pack habitat and have very thick blubber (maximum c.38—42 cm) and skin layers. Blubber acts as a thermal insulator in cold Arctic temperatures, and skin is thought to provide protection against ridged pack ice and rough seafloor. External markings from contact with ice and seafloor are noticeable on many individuals. Bowhead Whales are extremely long-lived. Old stone and ivory harpoon pieces have been recovered from blubber of Bowhead Whales, indicating a long life, and remarkably, bomb lance fragments that were manufactured in 1879-1885 were recovered in 1980 and 2007 from two dead Bowhead Whales. Obtaining accurate estimates of age for baleen whales has proven difficult. Promising methods tested for age determination in baleen whales include aspartic acid racemization (AAR) to read growth-layer groups in eye lenses and counting of ovarian corpora (scars left where a follicle has released an egg). Eye lenses of 42 Bowhead Whales landed by Alaskan Inuit were examined using AAR. The oldest female was estimated to be 88 years old, and the oldest male 145 years. A method combining total length and reproductive data has also proven useful for age estimates. Interestingly, a very old stone harpoon tip was recovered from one female aged with this method; her “corpora age” was 133 years old.

Habitat. Closely associated with Arctic pack ice. It has been suggested that these icy regions serve as a refuge from Killer Whales (Orcinus orca). Bowhead Whales select habitat in the Arctic that is characterized by high productivity and availability of zooplankton prey. In summer, they generally occupy continental slope waters with moderate ice conditions. In autumn, Bowhead Whales occupy inner shelf waters with relatively light ice conditions.

Food and Feeding. Stomach contents of Bowhead Whales have been well documented. Numerous prey species have been identified in their stomachs, but there is a clear preference for copepods (Calanus) and eupausiid krill. Mysid shrimps and gammarid amphipods are also sometimes prevalent in stomachs of Bowhead Whales. They skim the water’s surface to feed and also feed in the water column and at the seafloor. Bowhead Whales have been observed surface skimming synchronously, moving on their sides with mouths open, synchronously diving and surfacing while feeding, and cooperatively feeding, including in echelon formation. Typical feeding dives may last 5-15 minutes.

Breeding. Breeding of the Bowhead Whale is thought to occurin late winter and early spring. Sexual activity has been observed throughout the year. Breeding is thoughtto involve sperm competition, and like right whales, mating groups are often composed of a single female with multiple males competing for access. Estimated gestation is 13— 14 months. Young are born in spring, with a peak in May. Young Bowhead Whales are 470-500 cm long at birth. Total length at one year of age is ¢.820 cm. Length at sexual maturity is estimated to be 1300-1350 cm for females and 1200-1300 cm for males.

Activity patterns. Bowhead Whales are slow moving, and they are also observed breaching and fluke slapping at the surface. Flukes are lifted prior to deep dives. Data for eight Bowhead Whales equipped with satellite-monitored radio tags in the Beaufort and Chuckchi seas for approximately one month indicated that many dives were short, less than one minute in duration. Most dives were shallow to c¢.16 m. Five of the whales dove deeper than 100 m, with the deepest dive recorded at 352 m. Deeper dives, which occurred over the deep-water Mackenzie Canyon, were thought to be associated with feeding behavior. Bowhead Whales may be capable of dives with durations of up to approximately one hour. They can break through ice of ¢.60 cm thick and may sometimes make their way through ice floes in this manner.

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.

Bibliography. Alter et al. (2012), Brandon & Wade (2004), Burns et al. (1993), Citta et al. (2014), Everitt & Krogman (1979), Ferguson et al. (2010), Finley (1990a, 2001), Frasier, McLeod et al. (2007), George & Bockstoce (2008), George & Suydam (2006), George, Bada et al. (1999), George, Follmann et al. (2011), Haldiman & Tarpley (1993), Heide-Jargensen, Laidre, Jensen et al. (2006), Heide-Jorgensen, Laidre, Quakenbush & Citta (2012), Heide-Jergensen, Laidre, Wiig et al. (2010), Ivashchenko & Clapham (2012), IWC (2013), Jefferson et al. (2008), Koski et al. (2010), Kovacs et al. (2011), Krutzikowsky & Mate (2000), Laidre, Heide-Jergensen & Nielsen (2007), Laidre, Stirling et al. (2008), Lowry (1993), Lowry etal. (2004), MacLean (2002), Mate et al. (2000), Moore & DeMaster (1998), Moore & Reeves (1993), Moore, DeMaster & Dayton (2000), Moore, George etal. (2010), Moore, Stafford et al. (2012), Morin et al. (2012), Nerini et al. (1984), Nishiwaki & Kasuya (1970), O'Hara et al. (2002), Pomerleau, Ferguson & Walkusz (2011), Pomerleau, Patterson et al. (2011), Reeves & Heide-Jorgensen (1996), Reeves, Mitchell et al. (1983), Reeves, Rosa et al. (2012), Reilly et al. (2008l), Rice (1998), Robertson et al. (2013), Rosa et al. (2013), Rugh & Shelden (2009), Stirling (1997), Tervo, Parks, Christoffersen et al. (2011), Tervo, Parks & Miller (2009), Tyack & Clark (2000), Woodby & Botkin (1993), Wiirsig & Clark (1993), Wiirsig, Dorsey et al. (1989), Wirsig, Guerrero & Silber (1993).

Figures

1. North Atlantic Right Whale (Eubalaena glacialis), 2. North Pacific Right Whale (Fubalaena japonica), 3. Southern Right Whale (Fubalaena australis), 4. Bowhead Whale (Balaena mysticetus)

Distribution. Circumpolar in the N Atlantic Ocean (NE Canada-W Greenland and E Greenland, Svalbard, Barents and Kara seas) and N Pacific Ocean (Bering—Chuckchi-Beaufort seas and Sea of Okhotsk).