HSI Asia -- Marine Mammals // Orcas

In the wild, orcas (sometimes called "killer whales") have a relatively high mortality rate during infancy (perhaps as high as 50% through age one). However, if a calf survives to its first birthday, a male can expect an average life span of 30 years, while a female can expect an average life span of 50 years.

The maximum estimated life span for male orcas in the wild is 50–60 years. The maximum estimated life span for female orcas in the wild is 70–80 years.

Orca populations studied to date appear to have three basic social structures—"resident" (possessing life-long family bonds, living in large matrilineal groups, feeding mainly on fish, vocalizing in highly variable, complex "dialects"); "transients" (possessing more fluid, less persistent family bonds, living in smaller groups, feeding mainly on other marine mammals, vocalizing in less variable, less complex dialects); and "offshores" about which little is known.

The basic unit of resident orca society is a mother and all of her dependent offspring (approximately 10 years or younger) and her adult offspring as well, including her sons. Females will eventually spend less time with their mothers, as they begin producing calves of their own, but resident males appear to remain with their mothers for their entire lives. They leave for short periods to mate outside of their maternal group, but return to their mother afterward.

The best-studied populations of orcas are in Canada (British Columbia), the United States (Puget Sound and Alaska), Norway, and Patagonia. Some work has also been done in sub-Antarctic waters, the Antarctic, and off Siberia.

The world-wide population of orcas is unknown, but is probably several tens of thousands of animals. (The number often given is 100,000.) They are not endangered or threatened, although some stocks may be.

The orcas in Iceland appear to prefer to eat herring. In other parts of the world, they prefer salmon or other common species. Essentially they adjust their dietary habits to local ecology—this is known as having a "catholic" diet.

There are approximately 45–50 orcas in captivity world-wide, in the United States, Canada, Japan, France, and Argentina.