The killer whale, or orca (Orcinus orca) is the most widely distributed cetacean (e.g., whales, dolphins, and porpoises) species in the world.
Killer whales have a distinctive color pattern, with black dorsal and white ventral portions. They also have a conspicuous white patch above and behind the eye and a highly variable gray or white saddle behind the dorsal fin.
The species shows considerable size "dimorphism". Male adult killer whales can reach up to 32 feet (9.8 m) in length and can weigh nearly 22,000 pounds (10,000 kg); females can reach 28 feet (8.5 m) in length and can weigh up to 16,500 pounds (7,500 kg). From a distance, males are further identified by their tall, straight-backed dorsal fins; females have smaller and hook-shaped dorsals.
Sexual maturity of female killer whales is achieved when the whales reach lengths of approximately 15-18 feet (4.6 m-5.4 m), depending on geographic region. The gestation period for killer whales varies from 15-18 months, and birth may take place in any month. Calves are nursed for at least 1 year, and may be weaned between 1 and 2 years of age. The birth rate for killer whales is not well understood, but is estimated as every 5 years for an average period of 25 years.
Life expectancy for wild female killer whales is approximately 50 years, with maximum longevity estimated at 80-90 years. Male killer whales typically live for about 30 years, with maximum longevity estimated at 50-60 years.
The diet of killer whales is often geographic or population specific. In the eastern North Pacific, the "resident" killer whale populations mainly feed on salmonids such as Chinook and chum salmon, while the "transient" population feeds on other marine mammals, such as Dall's porpoises, Pacific white-sided dolphins, California and Steller sea lions, harbor seals, sea otters, and even large baleen whales. Off the coast of Norway, killer whales mainly feed on herring and other schooling fish, often in a coordinated manner. In waters off New Zealand, killer whales feed on stingrays and sharks. Finally, in Antarctic waters, some killer whales hunt marine mammals and penguins, while others (presumably belonging to a different population) are observed feeding on Antarctic toothfish (Dissostichus mawsoni) and other fish species.
Killer whales are highly social animals that occur primarily in pods, or groups, of up to 40-50 animals. The average group size varies among populations, but often ranges from 2 to 15 animals. Larger groups of up to several hundred individuals occasionally form, but are usually considered temporary groupings of smaller social units that probably congregate near seasonal concentrations of prey, for social interaction, or breeding. Single whales, usually adult males, also occur in many populations. Differences in spatial distribution, abundance, behavior, and availability of food resources probably account for much of the variation in group size among killer whale populations.
Like all cetaceans, killer whales depend heavily on underwater sound for orientation, feeding, and communication. Killer whales produce three categories of sounds: clicks, whistles, and pulsed calls. Clicks are believed to be used primarily for navigation and discriminating prey and other objects in the surrounding environment, but are also commonly heard during social interactions and may have a communicative function. Killer whale whistles and pulsed calls are believed to be used for communication and during social activities. Whistles are frequency modulated (pitch changes with time) sounds with multiple harmonics. Pulsed calls are the most common type of vocalization in killer whales and resemble squeaks, screams, and squawks to the human ear. Most calls are highly distinctive in structure, and are characterized by rapid changes in tone and pulse repetition rate. Many calls are repeated, with some clicks reaching up to 4,000 or more pulses per second.2
Killer whales of different populations have specific vocalization types. In addition, even within the same population, dialects are known to exist among different pods of "resident" populations in the eastern North Pacific.
Killer whales are most abundant in coastal habitats of temperate waters, especially in the high latitudes. Killer whales are seldom seen in tropical and offshore waters.
Killer whales are the most widely distributed marine mammals. They are found in all parts of the ocean and in most seas from the Arctic to the Antarctic. In the North Pacific Ocean, killer whales are often sighted from the eastern Bering Sea to the Aleutian Islands; in the waters of southeastern Alaska and the intercoastal waterways of British Columbia and Washington State; along the coasts of Washington, Oregon, and California; along the Russian coast in the Bering Sea and the Sea of Okhotsk; and on the eastern side of Sakhalin and the Kuril Islands, and the Sea of Japan. In the North Atlantic Ocean, sightings of killer whales are commonly documented up to the pack ice edge in Norwegian waters and around Iceland. In the South Atlantic and Pacific Oceans, killer whales are frequently sighted along the pack ice of Antarctica, and off the coasts of Patagonia, southern Argentina, and New Zealand.
Scientific studies have revealed many different populations/stocks (or even potentially subspecies) of killer whales worldwide. These different populations/stocks of killer whales may exhibit different dietary needs, behavior patterns, social structures, and habitat preferences. Therefore, crossbreeding is not expected to occur between different populations/stocks, in spite of the overlap between home ranges. Because of its cosmopolitan distribution, there is no global population assessment for killer whales.
Little information is available on the historical abundance of killer whales worldwide. Nevertheless, it is likely that many populations have declined significantly since 1800 in response to greatly diminished stocks of fish, whales, and pinnipeds (seals and sea lions) in the ocean. The population size of killer whales is difficult to measure in many areas because of their general scarcity as well as their widespread and often unpredictable movement patterns.
During the past few decades, populations have been surveyed primarily through the use of photo-identification studies or line-transect counts. Photo-identification catalogs for killer whales were first established in the early 1970s for the resident communities of Washington and British Columbia and have since been initiated for most areas where population studies have been undertaken. Line-transect surveys from ships or aircraft generally occur in large areas of open ocean where photo-identification is impractical. However, this technique cannot be used for gathering most demographic data, such as age of sexual maturity.
As top-level predators, killer whales occur in low densities throughout most of their geographic range. Densities are typically much greater in colder waters than in tropical regions. One estimate put the worldwide population of killer whales at over 100,000 animals. However, the most recent estimate revised this figure to a minimum of about 50,000 animals. In the northeastern Pacific, from California to the western Aleutian Islands and Bering Sea, at least 2,250-2,700 resident, transient, and offshore whales are currently thought to exist.
Although all killer whales are protected under the MMPA, and some are protected under the ESA, and have not been commercially harvested in the past 40 years within the U.S. waters, historic live capture for aquarium display and culling for depredation of fisheries reduced some killer whale populations, especially the SRKW stock. Today, these killer whales still face many threats caused by human activities, such as contaminants (e.g., PCBs), depletion of prey due to overfishing and habitat degradation, ship collisions, and oil spills. Additional threats may also include disturbance from such activities as noise from industrial and military activities, entanglement in fishing gear, and whale-watching. Outside U.S. waters, directed catch of killer whales still occurs, though these levels are presumed low.
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