Belugas in the wild range in size from 4 to 5.5m or more although it is unusual for them to grow much more than 4.5m. The males are generally 30-50cm longer than the female at physical maturity.(1)
Habitat seems to play a role in body size for the beluga whale. The smallest animals inhabit the White Sea and Hudson Bay. Mid-size whales inhabit the Eastern Canadian Arctic and the Gulf of St. Lawrence. The largest belugas are found off the shore of Greenland and the Okhotsk Sea. (2)
As the name Delphinapterus Leucus suggests (the white finless dolphin), they do not have a dorsal fin. They have a ridge or dorsal crest 1-3cm high and rises behind the blowhole midway along the back for approximately 50cm and is invariably marked with cuts and abrasions.(3). The skin on the top of their heads is very thick and the blubber is thin. These are probably an adaptation so that they can ram through ice to make breathing holes. (4) This crest along with the forehead is used to break through ice in the winter The absence of the dorsal fin may reduce heat loss and help to avoid abrasions by ice. (5)
Physically mature males display a marked upward curve of the flippers while females remain flat. This feature is sometimes used to distinguish adults in the wild. (6)
Colour at birth is dark grey and may have a brown or red tinge. The colour changes from slate grey, grey, to light grey. By about the 5th or 6th year the calf will be white with bluish tinge and turn pure white after that time. Pure white implies sexual maturity in females and sexual but not necessarily social maturity in males. (7) Their colouring helps them to hide from predators among the ice floes.
Physical maturity is reached by the 10th year. In maturity the flukes may retain a darker colour along the edges. In the winter the adult may appear to have a yellow wish colour which is lost during the summer. (8) One of the most outstanding characteristics of the beluga whale is that the vertebrae in their neck is not fused as in most other cetaceans. This gives the beluga the ability to turn its head. (9) It also makes them very subtle which helps them to avoid predators. With the use of their flippers and tail flukes they are also able to swim both forward and backwards.