Polar Bears in Alaska
POLAR BEAR
The polar bear’s scientific name, Ursus maritimus, means sea bear. Polar bears are the most carnivorous of the bear family. Alaska has two recognized polar bear populations, the Beaufort Sea and Chukchi/Bering Sea populations.
SIZE: Polar bears are large; males can weigh 1700 pounds (771 kg) and be eight to ten feet (2.4–3 m) long. Females reach a weight of 700 pounds (318 kg) and six to eight feet (1.8–2.4 m) in length. Compared
to the closely related brown bear, polar bears can weigh more, but they have a smaller head and longer neck. Their body is stocky, but they lack the large shoulder hump seen on brown bears.
COLOR: Polar bear colors range from pure white to yellowish to gray or brownish. The darker colors can be due to staining by seal blubber. The nose, skin and lips are black. Their pelage, or fur, consists of a thick undercoat and an abundance of long guard hairs.
SPEED: Polar bears can swim six miles per hour (9.7 km/hr) and can run 25 miles per hour (40 km/hr).
LONGEVITY: Polar bears can live at least 32 years in the wild.
REPRODUCTION: From late March through May male polar bears seek out females. They mate with as many as they can during the spring mating season. Mating usually occurs out on the sea ice. The fertilized egg does not implant until September, and it may not implant and develop if the female is unhealthy. This is called “delayed implantation.”
The female locates a suitable den site on either sea ice or land. The den is excavated in the snow, usually under a snow bank or on uplifted sea ice. An enlarged den chamber is used to give birth to the cubs (usually two), which occurs in December. Unlike black and brown bears, polar bears do not hibernate. The sole purpose of the den is to protect the bear family when the cubs are very young. The newborns weigh about a pound (0.5 kg) at birth, are blind and covered with fur. They grow quickly on rich bear milk which has a 30 percent fat content. The bears emerge from the den in the spring, late March or early April, after the cubs reach about 15 pounds (6.8 kg). They will continue to use the den until the cubs become acclimated to the outside environment; then they begin traveling on the drifting sea ice. The mother bear and her young stay together for about 2½ years before they separate and she breeds again.
Females do not breed until they are at least four years old and sometimes not until they are eight years old. They can produce young every three years, or about five litters during their lifetime, a low reproductive rate, but similar to that of brown bears.
SOCIAL STRUCTURE: Polar bears are usually solitary, except females with young, groups feeding on an abundant food patch such as a beached whale, or during the breeding season.
DISTRIBUTION: Polar bears can occur throughout the North Polar Region. They are most abundant near coastlines and the southern edge of the pack ice.
MOVEMENTS AND MIGRATION: The edge of the ice moves seasonally, and polar bear movements tend to follow the shifting ice south during the winter and north during the summer. In Alaska the southern extent of polar bears is St. Matthew Island and the Kuskokwim River delta in the Bering Sea. The extent of a polar bear’s annual movement, or its home range, is determined by food availability, weather, and ice and ocean conditions. Some polar bears may travel thousands of miles (>5000 km) each year in search of food, mates and den sites.
HABITAT: Polar bears use the ice and swim in the ocean in their search for prey. When the ice melts in summer they may be left stranded on land for months at a time.
PREY: Polar bears are primarily carnivores eating ringed seals, bearded seals, walruses, beluga whales, small mammals, birds and bird eggs. They also will eat carrion, including large whales washed up on beaches. Polar bears rarely attack and kill people. Since 1970 polar bears have killed seven people in Canada’s arctic region, and one person in Alaska.
PREDATORS: Polar bears may be killed by other, larger polar bears. Their only other natural predator is the orca and possibly Pacific sleeper sharks and Greenland sharks. People hunt polar bears for their hides and as trophies. Some people eat polar bear meat.
PREDATORY CHARACTERISTICS: Polar bears’ paws are adapted to their harsh environment. The paws of an adult can measure up to 12 inches (30 cm) across, allowing the bear to travel on thin ice. The black footpads are covered with bumps, and their sharp, 2-inch (5.1-cm) curved claws are adapted for traveling on the ice and securing prey. The large forepaws are used to paddle through the water, and the rear paws serve as steerage. Hair covers the bottoms of their feet.
The senses of smell and vision of the polar bear are very keen, probably superior to that of the brown bear. A polar bear’s teeth are longer, sharper and more widely spaced than those of the brown bear, adaptations suited to the polar bear’s diet of seals, walruses and small whales. Another adaptation that polar bears have is a layer of blubber over four inches (10.2 cm) thick which acts as insulation to keep polar bears warm, even when they are swimming in ice-filled waters. They are so well insulated that they must be careful not to overheat. Polar bears spend much of their time hunting their favored prey, the four-foot (1.2-m) long, 150-pound (68 kg) ringed seal. The bears prize the ringed seal’s thick layer of blubber, used to insulate the seal from the bitterly cold waters.
Polar bears lie in wait near active seal breathing holes and grab the seals when they come up to breathe. This is the technique used most often during the winter when the sea is mostly frozen over. During early summer, ringed seals bask in the warm sun. Their dark coloration can be spotted a long way off by the alert bear. The bear slowly and quietly stalks the seal, then, when about 20 feet (6.1 m) away, the bear charges, capturing the seal before it can escape.
In spring, adult seals will leave their very young pups in sheltered snow chambers on the ice near their breathing holes, so the female can dive for food. Polar bears will seek out these unsubstantial shelters and prey on the pups. When prey is plentiful polar bears will eat only the energy-rich blubber and skin, leaving the remains for younger inexperienced bears, arctic foxes and other scavengers.
Polar bears survive because they can manage through a feast-and-fasting lifestyle. When food is abundant they must take advantage of the situation. A beached whale carcass can attract dozens of polar bears. One bear may dominate, or own, the carcass, but if a specific polar bear protocol is followed, all incoming polar bears will be allowed to feast on the
whale. The trespassing bears beg in a submissive manner with a low-to-the-ground, slowly circling approach. This is followed by nose touching with the bear that owns the whale.
Polar bears will kill and eat beluga whales trapped in a small opening in a vast expanse of ice. Dozens of whales may be taken in this manner from a single, small opening. After eating, a polar bear is likely to be soiled with blood and blubber. They are careful to clean themselves, either in water or, if water is not available, in snow. A polar bear will carefully lick its chest, muzzle and paws. Females will lick their cubs to keep them clean and teach them how to wash in water and snow. Polar bears are careful to keep their fur clean, because soiled fur has reduced insulation properties and because their ability to blend in with the background of white also is reduced.
CURRENT STATUS: Polar bear populations have increased slowly in Alaska since the 1970s. The Alaska population of polar bears is estimated at 3000–5000 animals, and the world population of polar bears is estimated at 22,000–27,000 animals.
ECOLOGY/CONSERVATION: Under State of Alaska management, polar bear populations were decreasing and at risk. Alaska allowed hunting of polar bears from the ground and from aircraft, including from helicopters. With the passage of the Marine Mammal Protection Act in 1972, management authority of polar bears was transferred to the federal government. A moratorium was placed on hunting polar bears, except by Alaska Natives, and use of aircraft was prohibited. The hides and meat of polar bears are used by Alaska Natives, and the tanned hides are used in traditional
arts.
Still, the greatest threats to the survival of the polar bear now are due to human activities. Oil and gas development in the Arctic poses an increasing risk to bears. Oil spills in the Arctic are difficult or impossible to clean up. If the fur of a polar bear is contaminated with oil, the insulation value of the fur is reduced, stressing the animal. Ingesting oil by cleaning its fur or eating oil-contaminated prey and breathing toxic petroleum fumes could kill polar bears, affecting polar bear populations over a very large area. Contaminant levels, particularly PCBs and DDT, continue to increase in the Arctic. These toxic compounds concentrate as they move up the food web in a process called “biomagnification.” These contaminants have reached high levels in many Alaskan predators. Scientists are working to predict how these toxins ultimately will affect Alaska’s predators, ecosystems and people.
Global warming ultimately may exert the greatest impact on the Arctic. The size and thickness of the Arctic ice cap has diminished, altering polar bear habitat. During the summer many polar bears have difficulties securing food; some bears are stranded on land waiting for the ocean to freeze so that they can continue to hunt seal. Recent observations of drowned polar bears may be a hint of things to come for this species. Many polar bears are shot each year when
they find their way into villages and interact with the human residents. Polar bears depend upon the ice flows and cold temperatures, an environment for which they are adapted and are well suited.
References:
Wright, Bruce A. 2012. Harbingers of Climate Change, Dominance of a Top Predator, Pacific Sleeper Sharks and Greenland Sharks. In; Biological Diversity and Ecological Problems in Priamurie and Adjacent Territories. Regional Scientific Work with International Participants, Far Eastern Federal University for the Humanities. Issue 3.
Wright, Bruce A., 2011. Alaska Predators, Their Ecology and Conservation. Hancock House Publishing. 119 pages. http://www.hancockhouse.com/products/alapre.htm
Wright, B.A. 2009. Chukchi Sea Ice Out, In: Thoreau's Legacy: American Stories about Global Warming. Penguin Classics. New York, N.Y. http://www.us.penguingroup.com/static/pages/ebooks/thoreauslegacy/index.html
Other species:
Pacific sleeper sharks in Alaska
Salmon sharks in Alaska
Great white sharks in Alaska
Bald Eagle
Gyrfalcon
Great Horned Owl
Snowy Owl
Black Bears
Brown Bears
Orcas
Wolves
Wolverine
The polar bear’s scientific name, Ursus maritimus, means sea bear. Polar bears are the most carnivorous of the bear family. Alaska has two recognized polar bear populations, the Beaufort Sea and Chukchi/Bering Sea populations.
SIZE: Polar bears are large; males can weigh 1700 pounds (771 kg) and be eight to ten feet (2.4–3 m) long. Females reach a weight of 700 pounds (318 kg) and six to eight feet (1.8–2.4 m) in length. Compared
to the closely related brown bear, polar bears can weigh more, but they have a smaller head and longer neck. Their body is stocky, but they lack the large shoulder hump seen on brown bears.
COLOR: Polar bear colors range from pure white to yellowish to gray or brownish. The darker colors can be due to staining by seal blubber. The nose, skin and lips are black. Their pelage, or fur, consists of a thick undercoat and an abundance of long guard hairs.
SPEED: Polar bears can swim six miles per hour (9.7 km/hr) and can run 25 miles per hour (40 km/hr).
LONGEVITY: Polar bears can live at least 32 years in the wild.
REPRODUCTION: From late March through May male polar bears seek out females. They mate with as many as they can during the spring mating season. Mating usually occurs out on the sea ice. The fertilized egg does not implant until September, and it may not implant and develop if the female is unhealthy. This is called “delayed implantation.”
The female locates a suitable den site on either sea ice or land. The den is excavated in the snow, usually under a snow bank or on uplifted sea ice. An enlarged den chamber is used to give birth to the cubs (usually two), which occurs in December. Unlike black and brown bears, polar bears do not hibernate. The sole purpose of the den is to protect the bear family when the cubs are very young. The newborns weigh about a pound (0.5 kg) at birth, are blind and covered with fur. They grow quickly on rich bear milk which has a 30 percent fat content. The bears emerge from the den in the spring, late March or early April, after the cubs reach about 15 pounds (6.8 kg). They will continue to use the den until the cubs become acclimated to the outside environment; then they begin traveling on the drifting sea ice. The mother bear and her young stay together for about 2½ years before they separate and she breeds again.
Females do not breed until they are at least four years old and sometimes not until they are eight years old. They can produce young every three years, or about five litters during their lifetime, a low reproductive rate, but similar to that of brown bears.
SOCIAL STRUCTURE: Polar bears are usually solitary, except females with young, groups feeding on an abundant food patch such as a beached whale, or during the breeding season.
DISTRIBUTION: Polar bears can occur throughout the North Polar Region. They are most abundant near coastlines and the southern edge of the pack ice.
MOVEMENTS AND MIGRATION: The edge of the ice moves seasonally, and polar bear movements tend to follow the shifting ice south during the winter and north during the summer. In Alaska the southern extent of polar bears is St. Matthew Island and the Kuskokwim River delta in the Bering Sea. The extent of a polar bear’s annual movement, or its home range, is determined by food availability, weather, and ice and ocean conditions. Some polar bears may travel thousands of miles (>5000 km) each year in search of food, mates and den sites.
HABITAT: Polar bears use the ice and swim in the ocean in their search for prey. When the ice melts in summer they may be left stranded on land for months at a time.
PREY: Polar bears are primarily carnivores eating ringed seals, bearded seals, walruses, beluga whales, small mammals, birds and bird eggs. They also will eat carrion, including large whales washed up on beaches. Polar bears rarely attack and kill people. Since 1970 polar bears have killed seven people in Canada’s arctic region, and one person in Alaska.
PREDATORS: Polar bears may be killed by other, larger polar bears. Their only other natural predator is the orca and possibly Pacific sleeper sharks and Greenland sharks. People hunt polar bears for their hides and as trophies. Some people eat polar bear meat.
PREDATORY CHARACTERISTICS: Polar bears’ paws are adapted to their harsh environment. The paws of an adult can measure up to 12 inches (30 cm) across, allowing the bear to travel on thin ice. The black footpads are covered with bumps, and their sharp, 2-inch (5.1-cm) curved claws are adapted for traveling on the ice and securing prey. The large forepaws are used to paddle through the water, and the rear paws serve as steerage. Hair covers the bottoms of their feet.
The senses of smell and vision of the polar bear are very keen, probably superior to that of the brown bear. A polar bear’s teeth are longer, sharper and more widely spaced than those of the brown bear, adaptations suited to the polar bear’s diet of seals, walruses and small whales. Another adaptation that polar bears have is a layer of blubber over four inches (10.2 cm) thick which acts as insulation to keep polar bears warm, even when they are swimming in ice-filled waters. They are so well insulated that they must be careful not to overheat. Polar bears spend much of their time hunting their favored prey, the four-foot (1.2-m) long, 150-pound (68 kg) ringed seal. The bears prize the ringed seal’s thick layer of blubber, used to insulate the seal from the bitterly cold waters.
Polar bears lie in wait near active seal breathing holes and grab the seals when they come up to breathe. This is the technique used most often during the winter when the sea is mostly frozen over. During early summer, ringed seals bask in the warm sun. Their dark coloration can be spotted a long way off by the alert bear. The bear slowly and quietly stalks the seal, then, when about 20 feet (6.1 m) away, the bear charges, capturing the seal before it can escape.
In spring, adult seals will leave their very young pups in sheltered snow chambers on the ice near their breathing holes, so the female can dive for food. Polar bears will seek out these unsubstantial shelters and prey on the pups. When prey is plentiful polar bears will eat only the energy-rich blubber and skin, leaving the remains for younger inexperienced bears, arctic foxes and other scavengers.
Polar bears survive because they can manage through a feast-and-fasting lifestyle. When food is abundant they must take advantage of the situation. A beached whale carcass can attract dozens of polar bears. One bear may dominate, or own, the carcass, but if a specific polar bear protocol is followed, all incoming polar bears will be allowed to feast on the
whale. The trespassing bears beg in a submissive manner with a low-to-the-ground, slowly circling approach. This is followed by nose touching with the bear that owns the whale.
Polar bears will kill and eat beluga whales trapped in a small opening in a vast expanse of ice. Dozens of whales may be taken in this manner from a single, small opening. After eating, a polar bear is likely to be soiled with blood and blubber. They are careful to clean themselves, either in water or, if water is not available, in snow. A polar bear will carefully lick its chest, muzzle and paws. Females will lick their cubs to keep them clean and teach them how to wash in water and snow. Polar bears are careful to keep their fur clean, because soiled fur has reduced insulation properties and because their ability to blend in with the background of white also is reduced.
CURRENT STATUS: Polar bear populations have increased slowly in Alaska since the 1970s. The Alaska population of polar bears is estimated at 3000–5000 animals, and the world population of polar bears is estimated at 22,000–27,000 animals.
ECOLOGY/CONSERVATION: Under State of Alaska management, polar bear populations were decreasing and at risk. Alaska allowed hunting of polar bears from the ground and from aircraft, including from helicopters. With the passage of the Marine Mammal Protection Act in 1972, management authority of polar bears was transferred to the federal government. A moratorium was placed on hunting polar bears, except by Alaska Natives, and use of aircraft was prohibited. The hides and meat of polar bears are used by Alaska Natives, and the tanned hides are used in traditional
arts.
Still, the greatest threats to the survival of the polar bear now are due to human activities. Oil and gas development in the Arctic poses an increasing risk to bears. Oil spills in the Arctic are difficult or impossible to clean up. If the fur of a polar bear is contaminated with oil, the insulation value of the fur is reduced, stressing the animal. Ingesting oil by cleaning its fur or eating oil-contaminated prey and breathing toxic petroleum fumes could kill polar bears, affecting polar bear populations over a very large area. Contaminant levels, particularly PCBs and DDT, continue to increase in the Arctic. These toxic compounds concentrate as they move up the food web in a process called “biomagnification.” These contaminants have reached high levels in many Alaskan predators. Scientists are working to predict how these toxins ultimately will affect Alaska’s predators, ecosystems and people.
Global warming ultimately may exert the greatest impact on the Arctic. The size and thickness of the Arctic ice cap has diminished, altering polar bear habitat. During the summer many polar bears have difficulties securing food; some bears are stranded on land waiting for the ocean to freeze so that they can continue to hunt seal. Recent observations of drowned polar bears may be a hint of things to come for this species. Many polar bears are shot each year when
they find their way into villages and interact with the human residents. Polar bears depend upon the ice flows and cold temperatures, an environment for which they are adapted and are well suited.
References:
Wright, Bruce A. 2012. Harbingers of Climate Change, Dominance of a Top Predator, Pacific Sleeper Sharks and Greenland Sharks. In; Biological Diversity and Ecological Problems in Priamurie and Adjacent Territories. Regional Scientific Work with International Participants, Far Eastern Federal University for the Humanities. Issue 3.
Wright, Bruce A., 2011. Alaska Predators, Their Ecology and Conservation. Hancock House Publishing. 119 pages. http://www.hancockhouse.com/products/alapre.htm
Wright, B.A. 2009. Chukchi Sea Ice Out, In: Thoreau's Legacy: American Stories about Global Warming. Penguin Classics. New York, N.Y. http://www.us.penguingroup.com/static/pages/ebooks/thoreauslegacy/index.html
Other species:
Pacific sleeper sharks in Alaska
Salmon sharks in Alaska
Great white sharks in Alaska
Bald Eagle
Gyrfalcon
Great Horned Owl
Snowy Owl
Black Bears
Brown Bears
Orcas
Wolves
Wolverine