Bowhead whale

Physical Description

The bowhead is a mysticete whale, a suborder of cetaceans characterized by rows of baleen plates for feeding on plankton, a symmetrical skull and paired blowholes. The species is recognized by its large skull (it represents about a third of its body length), and the prominent upturned lower jaw. There are two rows of about 300 vertical baleen plates, which at 300-450 cm are the largest of any whale. There is no dorsal fin.

With these large heads and powerful bodies, bowhead whales are capable of breaking through sea ice at least 20cms thick: Inuit hunters in Alaska have reported whales surfacing through 60cms of ice.

Size

Adult bowheads have an average length of 15 to 18 meters, with a particulary large specimen reported at 19.8 meters and over 100,000 kg in weight.

Colour

Adult bowheads are entirely black except the front part of the lower jaw which is whitish. There are white patches on the belly and a gray area at the beginning of the tail.

Ecology & Habitat

Among the longest-lived animals on earth?

The species is essentially found in the arctic region, in association with ice floes. Its movement patterns are therefore influenced by the melting and freezing of the ice. During the summer season it visits bays, straits, and estuaries.

Social Structure

Bowheads have been reported to feed in groups of up to 14 animals in V-shape formation, while groups consisting of two adults and a calf also were seen to persist for at least a few weeks.

Bowheads are usually solitary or in groups of two or three individuals, who may aggregate by age and sex. Larger groups may be formed during migration; young specimens of the Bering Sea population move North first during Spring migration, followed by large males and females with calves.

Life Cycle

Because these whales do not have teeth - often used to estimate age in other mammals - it can be difficult to determine their age. However, data has shown that bowhead whales may be among the longest-lived animals on earth. Based on the recovery of stone harpoon tips in their blubber, and from analysis of eye tissue, scientists believe that the life-span of bowhead whales can be over 100 years. One individual in a study was believed to be more than 200 years old.

Breeding

Bowheads usually reproduce in the late winter, with births occuring between April and June of the year after (13 months gestation). They give birth to a single calf of 400 to 500cm every 3 to 6 years, which weans 6 to 12 months later.

Diet

Bowheads filter their food through baleen, opening their mouths and straining zooplankton from the surface, the water column, or the sea floor. Zooplankton includes copepods and small shrimp-like animals called euphausiids. Scientists estimate that a bowhead whale needs to eat about 100 tonnes of crustaceans each year.

They maintain a thick layer of blubber that insulates them from the icy arctic waters. Bowhead whales often congregate in the autumn in areas with rich food resources. One such area is Isabella Bay near Clyde River, Nunavut, Canada, which WWF is helping to preserve as a whale sanctuary.

Population & Distribution

A predilection for the freezing waters of the Arctic

Previous population and distribution

It is estimated there once were four distinct populations of bowheads. When the bowhead became rare off Greenland in the early 1700s, the hunting focus shifted to the west of the island. Areas between Greenland and eastern Canada also became overexploited by the mid-nineteenth century, followed by whales in the Bering Sea.

Current population and distribution

These whales are found in the waters of the Arctic Ocean, the Sea of Okhotsk, Hudson Bay and the Gulf of St. Lawrence in Canada, and the Bering, Chukchi, and Beaufort seas between Alaska and Russia.

They migrate within these waters rather than moving seasonally to more temperate waters like other great whales. The fact that they stay in the Arctic year-round, moving between summer feeding and wintering areas, make bowheads one of only three whale species that spend their entire lives in the Arctic.

There are thought to be around 10,000 individuals of this species. Less than 100 probably remain in the Svalbard-Barents Sea (Spitsbergen), a population classified as Critically Endangered by the IUCN, and 150-200 in the Okhotsk Sea. Other populations such as the Bering-Chukchi-Beaufort stock and the Davis Strait-Baffin Bay and Hudson Bay-Foxe Basin stocks are hunted by indigenous people in Canada and Russia.

Long-term monitoring efforts of the Bering-Chukchi-Beaufort population indicate that the population has been increasing in the 1980s and early 1990s, despite ongoing hunting. There is no information on other bowhead population trends.

What are the threats to the bowhead whale?

The tragedy of being economically viable

The bowhead whale has been a victim of its long baleens and thick blubber, that have made it the most economically valuable of all cetaceans.

Hunted by commercial whalers until the last century for oil, meat, and baleen, bowhead whales are today listed as endangered species in many countries. Some populations are faring better as a result. Native Alaskans and Canadian Inuit are allowed a limited subsistence hunt for bowhead whales from stable populations.

Modern threats include habitat loss and toxics, which accumulates in the Arctic and which may negatively affect the health and reproduction of bowhead whales.