Orcas or killer whales are large and striking members of the dolphin family that live in all the world’s oceans. There are several subspecies of orca, and there is an ongoing debate in the scientific community concerning their classification. The most intensely studied orcas are the Salish Sea orcas of the southwestern coast of British Columbia, Canada. Other groups that have been studied include Argentinian, Japanese, Icelandic and Russian Orcas.
Although the largest orca population is in the Antarctic, this population is difficult to study because of harsh climatic conditions.
The intensively studied Salish orcas of the Northeast Pacific are classified into three main groups, depending on behavior and habitat.
Scientists know the most about resident orcas, which live in coastal waters, feed primarily on fish and live in complex social groups.
There are also transient orcas living along the Pacific coast from Alaska to Mexico. These appear to be a separate subspecies, and possibly belong to the same extended family. They travel in small groups of two to six individuals, have less complex vocalization than resident orcas and feed mostly on marine mammals.
Less is known about the third group, offshore orcas, which were only discovered in 1988. These live in the open ocean and congregate in large groups. They feed on schooling fish and also possibly marine mammals and sharks.
Orcas appear to have a culture which they pass from one generation to the next. Different orca groups produce unique vocalizations. They also use various sophisticated hunting techniques that are often specific to a particular group.
Different orca populations specialize in hunting different prey: Greenland orcas feed on herring, northeast Pacific orcas feed on salmon, New Zealand orcas hunt rays and Japanese Orcas eat fish and squid. Some orcas have even been observed to prey on sea birds such as penguins, cormorants and gulls. Orcas also display a variety of hunting methods. Wave-hunting orcas create waves to wash resting seals off of ice floes while other members of their group wait to catch them, and Argentinian orcas sometimes deliberately strand themselves to catch their prey.
Orcas also have a highly complex social structure. Northeast Pacific resident orcas live in matrilines, groups consisting of a matriarch and her descendants. Pods are groups of up to four matrilines. While matrilines stay together, pods are more loosely connected and may separate for extended periods of time. All members of a resident pod have a similar dialect, composed of specific call patterns and structure, which calves probably learn from other pod members. A group of pods with a similar dialect forms a clan, and a group of clans which mingle regularly forms a community.
Transient pods are small, typically consisting of an adult female and one or two of her offspring, and are much less vocal than resident pods. All members of the North American west coast transient community use the same basic dialect.
Offshore orcas also appear to have their own group-specific dialects that are different from those of residents or transients.
Research on orca populations elsewhere in the world is not as advanced as the research in the Salish Sea. The Icelandic orca population is estimated to be over 6,000, but only 200 individuals have been identified. The Norwegian Killer Whale Project was established in 1987, and the count of Norwegian resident orca appears to be between 600 and 700. Since 1999, Russian orca research has identified 150 individuals in the Kamchatka area, with an additional 100 individuals at various stages of identification, and fewer than 200 individuals have been identified in New Zealand.
Orcas are highly intelligent and have a complex social structure which rivals that of the higher primates. There is still much that that is not known about them, and much research remains to be carried out on both the classification and the behavior of these fascinating sea mammals.