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By Suzanne Sessine
Geographic Range
Most common in Arctic and Antarctic waters, but also occurs in all other oceans.
Biogeographic Regions:
arctic ocean 
(native ); indian ocean (native ); atlantic ocean (native ); pacific ocean (native ).
Habitat
Killer whales are found in all oceans, but mostly in cooler waters. In the Antarctic they live amid pack-ice, but they are said not to extend beyond the ice-line in the Arctic ocean. They are oceanic for the most part, but will approach the shore when attracted by food resources.
Aquatic Biomes:
coastal .
Reproduction
Killer whales breed during the spring and summer.
Orcas are polygynous; each group, or pod, contains one breeding male and several breeding females.
Mating systems:
polygynous .
Although the whales may breed near the end of the year in some areas, Killer whales appear to breed in spring and summer off the coast of the state of Washington. The gestation period is around a year, and the young at birth are about two meters long.
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous .
Behavior
Orcas are highly social whales, travelling about in discrete social units called pods. The relationships within the pod are stable and may persist from one generation to the next. Each pod contains one adult male, several adult breeding females and a number of sub-adults of both sexes. Pod size may vary from as few as four to as many as forty. Small pods, which are split off from larger ones, are less stable and may die out within a generation, probably because the larger pods monopolize preferred food resources. The orcas hunt together, and this behavior accounts for the evolution of the social links that result in pod formation.
Key behaviors:
natatorial ; motile ; social .
Food Habits
Killer whales are versatile predators. They feed on a wide variety of species, ranging from fish to warm-blooded prey such as birds, seals or even other whales. They require 2.5 to 5 percent of their body weight in food each day. making access to a substantial and reliable food source important. Fish and squid probably make up the bulk of their diet, with some pods (see Behavior and Social Systems) specializing in warm-blooded prey. Methods for feeding on squid are unknown, but when hunting in packs the whales trap and atack prey simultaneously.
Animal Foods:
birds; mammals; fish; mollusks.
Economic Importance for Humans: Negative
May interfere with commercial fishermen.
Economic Importance for Humans: Positive
Many fishermen use orcas to catch fish that the pods have driven together while hunting.
Conservation Status
Though orcas have no official status, a decline in populations has been recorded. Possible reasons for the apparent decline in numbers include exploitation by whalers, killing by angry fishermen (the whales eat their intended catch), declining food stocks (due to overfishing), pollution, and disease. Except for waters around Iceland and Antarctica, orca populations may be suffering. Some gentically isolated populations may even be endangered.
Other Comments
The worldwide distribution of Orcinus orca may be related to its omnivorous diet and remarkable temperature tolerance.
Contributors
Suzanne Sessine (author), University of Michigan.
