Description
The largest of the toothed whales, this species has a disproportionately large head, especially in males, that dominates the body. Skin posterior to the head appears corrugated or shriveled. Color is gray with a lighter area on belly and forehead; skin is white around the mouth. These whales have a distinct dorsal hump, usually rounded or obtuse, about two-thirds of the way behind their snout. Immediately behind the hump, a series of knuckles are visible when whale arches its back before diving (Alaska Geographic Society 1996). Blowhole is set forward on the head and skewed strongly to the left. Males are roughly one-third longer than females (males 18.3 m, females 11 m) and twice as a heavy. There are 20-26 pairs of large, conical teeth along the lower jaw that fit into sockets in the upper jaw (Reeves et al. 2002).
Habitat
Pelagic, prefers deep water, sometimes around islands or in shallow shelf waters (e.g., 40-70 m; Scott and Sadove 1997). Tend to occur in highest densities near productive waters, and often near steep drop-offs or strong oceanographic features, e.g. edges of continental shelves, large islands, and offshore banks and over submarine trenches and canyons (Gosho et al. 1984, Reeves and Whitehead 1997, Gregr and Trites 2001, Whitehead 2003). Females generally restricted to waters with surface temperatures warmer than about 15 degrees C and rarely found in waters less than 1000 m deep. Males, although primarily found in deep water, are sometimes found in waters 200 to 1000 m deep (Reeves and Whitehead 1997).
Ecology
Basic social unit is mixed school of adult females plus their calves and juveniles (usually about 20-40 individuals). As males grow older they leave this group and form bachelor schools (of variable sizes up to about 50 individuals). The largest males tend to be solitary (but see Christal and Whitehead 1997). Likely the world's deepest diving mammal (documented at 2,500 m.).
Reproduction
Gestation lasts 14-15 months. Births occur May-September in Northern Hemisphere, November-March in Southern Hemisphere. Single young is produced every 3-6 years. Young are weaned in about 1.5-3.5 years, though young may continue to nurse for several years. Females sexually mature at 7-11 years; pregnancy rate gradually declines after age 14. Males may not breed until about 25 years old. May up to at least 60-70 years.