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Polar Bears And Seals

The Polar Bear

Ursus maritimus

The polar bear or the sea/ice bear are the world's largest land predators. They can be found in the Artic, the U.S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway. Each of these countries either banned hunting or established rules for how many polar bears could be hunted within its own boundaries. These rules help keep polar bear populations stable. Today, 25,000 to 40,000 polar bears roam the Arctic.

Around the age of four or five the female polar bear can start having babies. They usually only have two cubs and they have these babies in a cave they've dug in a large snow drift. They stay there over winter and come out in spring with the babies.

The babies are much smaller than human babies when they're born. They are the size of a rat and weigh little more than a pound. They can grow to full man size in a year if they have lots of food.

Male polar bears may grow 10 feet tall and weigh over 1400 pounds. Females reach seven feet and weigh 650 pounds. In the wild polar bears live up to age 25.

Despite what we think, a polar bear's fur is not white. Each hair is clear hollow tube. Polar bears look white because each hollow hair reflects the light. On sunny days, it traps the sun's infrared heat and keeps the bear warm at 98 degrees F (when they're resting).

Polar bear fur is oily and water repellent. The hairs don't mat when wet, allowing the polar bears to easily shake free of water and any ice that may form after swimming.

Polar bears have wide front paws with slightly webbed toes that help them swim. They paddle with their front feet and steer with their hind feet. Paw pads with rough surfaces help prevent polar bears from slipping up on the ice.

Polar bears have been known to swim 100 miles (161 kilometers) at a stretch.

Polar bears primarily eat seals. They often rest silently at a seal’s breathing hole in the ice, waiting for a seal in the water to surface. Once the seal comes up, the bear will spring and sink its jagged teeth into the seal’s head.

Sometimes the polar bear stalks its prey. It may see a seal lying near its breathing hole and slowly move toward it, then charge it, biting its head or grabbing it with its massive claws. A polar bear may also hunt by swimming beneath the ice.

Humans are the polar bears only predator. Baby polar bears often starve. In fact, 70 percent do not live to their third birthday. Sometimes seals are hard to find, especially in the summer when the ice has melted. All across the Arctic, man is moving in to mine oil and coal and there is less space for the polar bear to live. Oil spills can be very dangerous. A bear with oil on its coat cannot regulate its body temperature properly. If the bear eats the oil while grooming it could die. Man made pollution is also a cause of death. At each stage of the food chain, pollutants get more concentrated. By the end when the polar bear eats the seal and it could be lethal.

Seals, Sea Lions, and Walrus: Pinnipeds

Pinnipeds are carnivores that have adapted to an amphibious marine existence. They forage at sea but most come ashore or onto ice at some time of the year to mate, give birth, suckle their young, or to molt. Many of their anatomical features reflect compromises needed to succeed in both marine and terrestrial environments. Externally, pinnipeds share many characteristics with terrestrial carnivores (fissipeds) due to their need for mobility on land.

Pinnipeds have four webbed flippers used to propel their spindle-shaped bodies. Their sensory organs are adapted to function both in air and water: large eyes and well-developed whiskers allow feeding in dimly lit water; tail and external ears are small, limiting drag. Pinnipeds have retained canine teeth but molars are modified for consuming prey whole. All have fur, which is shed or molted annually, but are insulated primarily by blubber. Pinnipeds are present in habitats ranging from ice to tropics, coastal to pelagic waters, and may live a migratory or sedentary existence. They are opportunistic feeders and consume their varied prey whole or in chunks. Many pinnipeds are capable of long, deep repetitive dives (to 4500 ft depths and 2 hours). This phenomenal diving ability is possible because of several physiological traits shared by cetaceans, such as high blood volume and reduced heart rate.

Family Characteristics of Alaska Pinnipeds

Representatives of all three pinniped families are present in Alaska waters.

Otariidae ("eared" seals)

Otariids have visible external ear flaps (pinnae) and an elongate neck. They swim using their long front flippers for propulsion and hind flippers for steering. On land, otariids are agile and quadrupedal: able to pull their hind flippers up under the body and extend the front flippers for four-legged movement.

Adult otariids are sexually dimorphic: males are nearly twice as large as females, and have thickened necks and pronounced skull crests. Females breed with dominant males that establish and defend territories on breeding beaches or rookeries. Pups are born on the rookeries, suckling for the first 3–5 months. They may be dependent on their mothers for a year or more.

Phocidae ("earless" seals)

Phocids have no visible external ear flaps (pinnae). They have short necks and short front flippers, and cannot pull their hind flippers under the body while on land. Although graceful swimmers, phocids are not agile on land and typically "phocidulate"; that is, they move by undulating or heaving the body in a caterpillar-like manner.

Sexual dimorphism is rare in adult phocids (seen only in elephant seals); males and females are generally similar in size and shape. Phocids breed in the water, on shore, or on ice, but (except for elephant seals) don't breed on rookeries. Pups grow at an incredibly fast rate and are weaned young and abruptly after brief lactation during which their mothers probably fast.

Odobenidae (walrus)

The walrus body form combines phocid and otariid traits. They have no external ear flaps (pinnae) but move quadrupedally on land. The upper canines in both sexes elongate and develop into tusks.