Bioacoustics of Delphinapterus leucas

Activity patterns. While in estuaries, Belugas have been observed rubbing on the bottom and surfacing with mud on their heads. This behavior is thought to accelerate sloughing of molting skin in early summer. In estuaries, they are often seen spy-hopping, tail-slapping, and chasing and rubbing against each other. During these social activities, many vocalizations can be heard. Rosette formations have also been described where several Belugas quietly face each other with their bodies radiating out. Most dives in coastal areas are shallow but, when offshore, Belugas of both sexes frequently dive through the water column down to the seabed to depths of at least 500 m; some dives even go down to 800 m. Young are unable to make these deep dives and remain near the surface while their mothers forage. Adult male Belugas are capable of deeper dives; a record dive of ¢.1000 m has been measured. Both sexes make dives that last 10-25 minutes. Winter dives are longer, on average, than summer dives because of deeper seabeds in their wintering areas.

Descriptive notes. Total length 300-450 cm; weight 500-1600 kg. Male Belugas are heavier and larger than females. Size varies geographically, with larger individuals in Arctic regions than in subarctic regions. Belugas are rotund, with bulging midsections when fat. They have visible neck regions, which in healthy adults and particularly males give the appearance of shoulders. Unlike most other whales, cervical vertebrae of Belugas are not fused, and they can move their head quite well, probably an adaptation to life in shallow waters and under jumbled sea ice. They have small blunt heads with short beaks, and their mouths curve upward toward the eyes. Belugas have 8-11 blunt, uniform-looking teeth on both sides of upper and lower jaws, up to 40 in total. Their rostrums have globe-like melons, lumps offatty tissue that are used as acoustic lens to focus echolocation signals. Blowhole opens behind the melon just above the eyes. Dorsal ridge runs along mid-back, starting well behind head and flattening before tailstock. Belugas are born pink, white, or gray and become slate-gray in their first month. They progressively whiten over the entire body with age. Adult Belugas are entirely white, except for edges of fins, tail flukes, and dorsal ridges, which retain some dark pigment. In spring and early summer, Belugas may appear yellow when they are shedding epidermal skin during annual molt. This is most apparent in the Hudson Bay region where skin molt is rapid. Such a rapid molt has not been observed for Belugas elsewhere and may simply be more gradual in other parts of their distribution.