Bowhead whales in alaska

Bowhead whales (Balaena mysticetus) are the only mysticete (baleen) whales that spend their entire lives near sea ice and do not migrate to temperate or tropical waters to calve. Bowheads are well adapted for living in arctic and subarctic waters—they have very thick blubber, up to 1½ feet (.5 m), which is used for insulation, food storage, and padding, and heavy bone structure in their skulls for breaking ice. Bowheads are the most important subsistence animal, both culturally and nutritionally, for most northwestern Alaska coastal Eskimos. The northern Inupiaq and Yupik names for bowheads are “agviq” and “aghveq.”

General description: Bowheads are large, robust whales and their shape is much less streamlined than most other baleen whales. They have the largest mouth and head in the animal kingdom, about one- third of their body length. The upper jaw is arched upward, and paired blowholes are located at the peak of the elevated “crown.” This large, bow-shaped head distinguishes bowheads from other whales.

Bowhead calves are gray and adults are black with varying amounts of white on their chins, bellies, and tail areas. The white patches plus scars sometimes make it possible for airborne researchers to identify individuals. Their skin is smooth and nearly free of external parasites. Bowheads have short, wide flippers. Their flukes are very broad, equalling one-third of the body length.

Distribution and migration: Bowhead distribution was nearly circumpolar in the northern hemisphere. Commercial whaling greatly reduced bowhead numbers and only remnant populations remain in most of their original range.

The Bering Sea stock, which is the only population of bowhead whales that survives in significant numbers, follows a 3,600 mile (5800 km) migration route. They winter in the Bering Sea in polynyas (areas of consistently open water within pack ice) and at the edge of the pack ice. During late March and April, bowheads move north through the Bering Strait as the pack ice retreats. Most bowheads follow leads, or cracks, in the ice through the Chukchi Sea along the Alaska coast to Point Barrow. They travel offshore across the Beaufort Sea and arrive in Canadian waters from mid-May through June. The bowheads spend the summer in the Canadian Beaufort Sea, then migrate west along the continental shelf of the Beaufort Sea to Point Barrow from August through October. Next, the whales cross the Chukchi Sea and travel south along the Russian coast, passing through the Bering Strait by November.

Life history: Mating probably occurs during late winter and spring. The gestation period is 13 to 14 months. Most bowhead whales calve during April, May, or early June. After plunging from the internal body temperature of their mothers into near freezing water, the newborns must begin swimming north with the migrating herd almost immediately.

Bowhead whales are shorter but heavier at birth than most other baleen whales. The calves are about 14 feet (4.3 m) long and weigh about 2,000 pounds (907 kg) when they are born. In comparison, gray whale newborns are 16 feet (4.9 m) long and weigh 1,500 pounds (680 kg). Bowheads calve at about three to four year intervals.

Bowheads grow to about 26 feet (8 m) during their first year; then grow very slowly after weaning. Female bowheads become sexually mature at 41 to 46 feet (12.5 - 14 m) and probably at an age exceeding 15 years. Maximum size of bowheads is about 60 feet (18.3 m) and over 120,000 pounds (54,500 kg). Bowhead age determination is difficult, but their life span is probably similar to humans.

Food habits: The bowhead feeding mechanism is most proficient at filtering a “thin soup” rather than gulping dense masses of prey. Instead of having grooved expandable throats like most other baleen whales, bowheads have very large mouths to maximize the amount of water taken in and to hold captured food.

Bowheads feed by swimming with their mouths open and straining zooplankton out of the water with their baleen. Each bowhead carries about 660 baleen plates which hang down in two racks, one from each side of the upper jaw. The baleen plates are made up of a horn-like substance and may be up to 13 feet (4 m) long. The inner margins of the baleen plates are fringed with fine bristles that act as a hairy curtain to sieve food out of the water.

Bowheads feed at all depths, from the surface to the bottom. Their primary foods are copepods, euphausiids, and other invertebrates, typically 0.12 - 1.18 inches (3 - 30 mm) long. Bowheads feed year- round in the Beaufort, Chukchi, and Bering seas. They use a variety of strategies, including feeding under ice and swimming in groups in V-shaped formation, to increase feeding efficiency.

Behavior: Bowheads often depend for survival upon their ability to travel through ice-dominated waters. Researchers using hydrophones have detected bowheads traveling through lead systems that appear to be completely covered by ice. When bowheads can't find open water, they push up hummocks in thin ice or break holes in ice up to 2 feet (.6 m) thick.

Bowheads swim fairly slowly, generally 2 to 4 miles per hour (3 - 6 km/hr). When migrating they make long dives, generally from 6 to 17 minutes, and then usually surface for a series of four to nine blows. Dives of up to 33 minutes have been recorded.

Bowhead whales are very vocal and use underwater sounds to communicate while traveling, feeding, and socializing. Some bowheads produce long repetitive songs that may be related to mating display. They also breach, tail slap, and spy-hop, which may also be mating display. Sexual activity occurs between pairs and in boisterous groups of several males and one or two females.

Predators and other mortality: Humans and killer whales are the only major predators of bowheads. Scars from killer whale teeth and ship propellers are sometimes found on their backs and flukes. Some bowheads die from becoming wrapped in fishing gear lines. Oil spills are a serious potential danger to bowheads. Ice sometimes blocks their movements, and they may starve or suffocate if they cannot get to open water.

Population size: Before commercial whaling, there were over 50,000 bowhead whales worldwide. Between the 1600s and 1800s, the eastern arctic stocks of bowheads were reduced from over 30,000 animals to less than 1,000. They remain severely depleted. The Bering Sea stock originally numbered about 18,000 whales and was greatly reduced in the 1800s and early 1900s. It is currently increasing and the population estimate was 6,400 to 9,200 in 1992.

Human use: Bowheads have been a favored whale for hunting for at least 2,000 years because they produce large quantities of oil, baleen, meat, and muktuk (skin with blubber); because they are slow and nonaggressive; and because they float when they are killed. Only aboriginal subsistence whaling is currently allowed. Alaska Eskimo whalers use handheld weapons and skin boats propelled by paddles to pursue bowheads during the spring hunt and motor-driven boats during the fall. The hunt is managed by the Alaska Eskimo Whaling Commission, representing ten whaling villages in northwestern Alaska, under an agreement with the National Oceanic and Atmospheric Association. A quota was established by the International Whaling Commission, and 41 whales were allowed to be landed in 1993.

source: http://www.adfg.state.ak.us/pubs/notebook/marine/bowhead.php