Beluga Whale at Sea World in San Diego, California
The Beluga Whale or White Whale (Delphinapterus leucas) is an Arctic and sub-arctic species of cetacean. This marine mammal is commonly referred to simply as the Beluga.
This small whale can be up to 5 metres (16 ft) long, larger than all but the largest dolphins but smaller than most other toothed whales. Males are generally larger than the female - males can weigh 1,360 kg (3,000 pounds) and females about 900 kg (one ton).
The beluga moves in Arctic and sub-Arctic waters ranging from 50° N to 80° N. There is also an isolated population which travels in the St. Lawrence River estuary and the Saguenay fjord, around the village of Tadoussac, Quebec. There is also an endangered population that lives in the Cook Inlet, Alaska. Beluga whales are highly sociable creatures.
The absence of the dorsal fin is reflected in the genus name of the species - apterus is the Greek word for "wingless". The evolutionary preference for a dorsal ridge in favour of a fin is believed by scientists to be adaptation to under-ice conditions, or possibly as a way of preserving heat. Like in other cetaceans the thyroid gland is relatively large compared to terrestrial mammals (three times per weight as a horse) and may help to sustain higher metabolism during the summer estuarine occupations.
The body of the Beluga is rotund, particularly when well-fed, and tapers smoothly to both the head and tail. The tail fin grows and becomes increasingly ornately curved as the animal ages. The flippers are broad and short - making them almost square-shaped.
The global population of beluga today stands at about 100,000. Although this number is much greater than that of other cetaceans, it is much smaller than historical populations before decades of over-hunting. There are estimated to be 40,000 individuals in the Beaufort Sea, 25,045 in Hudson Bay, 18,500 in the Bering Sea and 28,008 in the Canadian Low Arctic. The population in the St. Lawrence estuary is estimated to be around 1000. They are considered an excellent sentinel species and indicator of the health of, and changes in, the environment. This is as they are long lived, on top of the food web, with large amounts of fat and blubber, relatively well studied for a cetacean, and still somewhat common.
The beluga's natural predators are polar bears, who hunt when the whales become encircled by ice during winter. In these cases many miles of ice separate groups of Belugas from the open ocean, and as a result they are unable to leave until the ice melts in spring. During this period belugas do not offer much resistance to bear attacks due to their low energy reserves.