|- valign=top |Kingdom:||Animalia |- valign=top |Phylum:||Chordata |- valign=top |Class:||Mammalia |- valign=top |Order:||Cetacea |- valign=top |Family:||Delphinidae |- valign=top |Genus:||Orcinus |- valign=top |Species:||O. orca |} |- style="text-align:center;" ! style="background: pink;" | Binomial name |- style="text-align:center;" |Orcinus orca
Linnaeus, 1758 |- | style="text-align:center;" |
Orca range (in blue) |} The orca (Orcinus orca), commonly known as the killer whale, is the largest member of the oceanic dolphin family. It is the second-most widely distributed mammal on Earth (after humans) and is found in all the world's oceans. It is also a versatile predator, eating fish, turtles, birds, seals, sharks and even other juvenile and small cetaceans. This puts the orca at the pinnacle of the marine food chain. The name "killer whale" reflects the animal's reputation as a magnificent and fearsome sea mammal that goes as far back as Pliny the Elder's description of the species. Today it is recognized that the orca is neither a whale (except in the broadest sense, i.e., the sense that all cetaceans are whales) nor a danger to humans; no attack on a human by an orca in the wild has ever been recorded, though there have been isolated reports of captive orcas attacking their handlers at marine theme parks.
Since the 1960s, "orca" (plural "orcas") has steadily grown in popularity as the common name used to identify the species in English and is now more popular than the traditional name, "killer whale", among those in the field (though the latter is still widely used by the general public).
There are several reasons for the change. First, having the word whale in the name of a species that is really a dolphin causes confusion. Second, the species is called orca in most other European languages and, as there has been a steady increase in the amount of international research into the species, there has been a convergence in naming. Further, the killer in "killer whale" is often wrongly assumed to imply that the creature will kill humans. This historical reputation is downplayed by rebranding the species with a different name.
It is commonly accepted that "killer whale" is an 18th-century mistranslation of the name given by Spanish sailors for the species — which would properly be translated as whale-killer. That the original name was itself a mistranslation has also strengthened the case for "orca".
However there are many who prefer the original name on account of the fact that it is a good description of a species that does indeed kill many animals, including other cetaceans. These supporters of the original name point out that the naming heritage is not limited to Spanish sailors. Indeed the Latin name orca may be derived from Orcus, the god of the Underworld. To the Haida tribes of British Columbia, the animal was called skana or killing demon. The Japanese call them shachi (鯱), whose kanji character combines the radicals for fish (魚) and tiger (虎).
Taxonomy and evolution
The orca is the sole species in the genus Orcinus. It is one of thirty-five species in the dolphin family. Like the sperm whale genus Physeter, Orcinus is a genus with a single, abundant species with no immediate relatives from a cladistic point of view, thus palaeontologists believe that the orca is a prime candidate to have an anagenetic evolutionary history — that is the evolution of ancestral to descendant species without splitting of the lineage. If true, this would make the orca one of the oldest dolphin species, although it is unlikely to be as old as the family itself, which is known to date back at least five million years.
The animals are distinctively marked, with a black back, white chest and sides and a white patch above and behind the eye. They have a heavy and stocky body and a large dorsal fin. Males can be up to 9.5m long (a little over 31 feet) and weigh in excess of 6 tons; females are smaller, reaching up to 8.5m (about 28 feet) and a weight of about 5 tons. Calves at birth weigh about 180 kg and are about 2.4m long (about 8 feet). At about 1.8m (about 6 feet), the dorsal fin of the male is taller than the female's, and more upright.
Large male orcas are very distinctive and are unlikely to be confused with any other sea creature. When seen from a distance in temperate waters, females and juveniles can be confused with various other species, such as the False Killer Whale or Risso's Dolphin.
Most life history data about orcas has been obtained from long-term surveys of the population off the coasts of British Columbia and Washington and by monitoring captive whales. Due to the completeness of the study and highly structured nature of the pods in this population, the information is detailed and accurate; however, transient groups and groups in other oceans may have slightly different characteristics. Females become mature at around 15 years of age. From then they have periods of polyestrous cycling with non-cycling periods of between three and sixteen months. The gestation period varies from fifteen to eighteen months. Mothers calve, with a single offspring, about once every five years. In analysed resident pods, birth occurs at any time of year, with the most popular months being those in winter. New-born mortality is very high — one survey suggested that nearly half of all calves fail to reach the age of six months. Calves nurse for up to two years, but will start to take solid food at about twelve months. Mothers breed until the age of 40, meaning that on average they raise five children. Typically females live to the age of fifty, but may survive well into their eighties or nineties in exceptional cases. Males become sexually active at the age of 15, and live to about 30 on average, and to 50 in exceptional cases.
The orca is the second-most widely distributed mammal in the world, after the human. They are found in all oceans and most seas including (unusually for cetaceans) the Mediterranean and Arabian Seas. Cooler temperate and polar regions are preferred, however. Although sometimes spotted in deep water, coastal areas are generally preferred to pelagic environments.
The orca is particularly highly concentrated in the northeast Pacific Basin , where Canada curves into Alaska, off the coast of Iceland and off the coast of northern Norway. They are regularly sighted in Antarctic waters right up to the ice-pack and indeed are believed to venture under the pack and survive breathing in air pockets like the beluga does. In the Arctic, however, the species is rarely seen in winter, as it does not approach the ice pack. It does visit these waters during summer.
Information for off-shore regions and tropical waters is more scarce but widespread, if not frequent; sightings indicate that the orca can survive in most water temperatures. No estimate for the total worldwide population exists. Local estimates include 70-80,000 in the Antarctic, 8,000 in the tropical Pacific (although tropical waters are not the orca's preferred environment, the sheer size of this area — 19 million square kilometres — means there are thousands of whales), up to 2,000 off Japan, 1,500 off the cooler northeast Pacific and 1,500 off Norway. Adding very rough estimates for unsurveyed areas, the total population could be around 100,000.
Orcas have a complex system of social grouping. The basic unit is the matriline, which consists of a single female orca (the matriarch) and her descendants. The sons and daughters of the matriarch form part of the line as do the sons and daughters of those daughters (the sons and daughters of the sons join the matriline of their mates) and so on down the family tree. Because females can live for up to ninety years, it is not uncommon for four or even five generations of orcas living in the same line. These matrilineal groups are highly stable over many years. Individuals will only split off from their matrilineal group for up to a few hours at a time in order to mate or forage. No permanent casting out of an individual from a matriline has ever been recorded. The average matriline size as recorded in northeast Pacific waters is nine animals.
Matrilines tend to congregate with a small number of other matrilines to form a pod, consisting on average of about 18 animals. Members of a pod all have the same dialect (see the song section below) and consist of closely related matriline fragments. Unlike matrilines, pods will split apart for days or weeks at a time in order to carry out foraging before joining back together. The largest recorded pod is 49 animals.
The next level of grouping is the clan. A clan consists of those pods which have a similar dialect. Again the relationship between pods appears to be genealogical, consisting of fragments of families with a common heritage on the maternal side. Different clans can occupy the same geographical area; pods from different clans are often recorded traveling together. When resident pods come together to travel as a clan, they greet each other by forming two parallel lines akin to a face-off before mingling with each other.
The final layer of association, perhaps more arbitrary and devised by humans rather than the other very natural divisions, is called the community and is loosely defined as the set of clans that are regularly seen mixing with each other. Communities do not follow discernible familial or vocal patterns.
In the northeast Pacific there have been three communities identified:
- The southern community (1 clan, 3 pods, 83 orcas as of 2000)
- The northern community (3 clans, 16 pods, 214 orcas as of 2000)
- The south Alaskan community (2 clans, 11 pods, 211 orcas as of 2000)
It should be emphasized that these hierarchies are valid for resident groups only. Transient, mammal-eating groups are generally smaller because, although they too are based on matrilines, males are much more likely to split off to live a solitary life. However, transient groups still have a loose connection defined by their dialect.
The day-to-day behaviour of orcas is generally divided into four activities: foraging, traveling, resting and socializing. Orcas are generally enthusiastic in their socializing, exhibiting a wide range of breaching, spyhopping, tail-slapping and head-stands. All-male groups often interact with erect Censored pagees. Whether this interaction is part of play or a display of dominance is not known.
The array of species on which orcas prey is extremely diverse. Specific populations tend to specialize on particular prey species, even at the expense of ignoring other potential prey. For example, some populations in the Norwegian and Greenland sea specialise on herring and follow that fish's migratory path to the Norwegian coast each autumn. Other populations in the area prey on seals. Orcas are the only mammals with this diversification of feeding among overlapping species.
The orca is the only cetacean species to regularly prey on other cetaceans. Twenty-two species have been recorded as preyed on, either through an examination of stomach contents, examining scarring on the other cetacean's body, or by simply observing the feeding activity. Pods of orcas will even prey upon larger whales such as Fin Whales, Minke Whales, Grey Whales, or even young Blue Whales. A group of orcas take a young Blue Whale by chasing it and its mother through the sea, wearing them out. Eventually the orcas manage to separate the pair and then surround the younger whale, thereby preventing it from returning to the sea's surface in order to breathe. Once the whale has drowned, the orcas are free to feed on it.
There has also been one recorded case of probable orca cannibalism. A study carried out by V. I. Shevenko in the temperate areas of the South Pacific in 1975 recorded two male orca whose stomachs contained the remains of other orcas. Of the 30 orcas captured and examined in this survey, 11 had empty stomachs — an unusually high percentage that indicates the orca were forced to cannibalism through a lack of food.
More commonly, orcas prey on 30 species of fish, particularly salmon, herring, tuna, chinook and coho . Basking sharks, oceanic whitetip shark s, and very occasionally even great white sharks are taken for their nutrient-rich livers. There is also believed to be an element of competition elimination in taking these sharks. Other marine mammals, including most species of seal and sea lion, are also taken by polar populations. Walrus and sea otters are taken less frequently. Seven species of bird are also taken, including all penguin species as well as sea birds such as cormorants. Cephalopods, such as octopi and a wide range of squid, are also targets.
Orcas are very inventive and playful in their killing. They sometimes will throw seals to one another through the air in order to stun and kill the animal. While salmon are usually hunted by a single orca or a small group of individuals, herring are often caught using carousel feeding : the orcas force the herring into a tight ball by releasing bursts of bubbles or flashing their white underside. The orcas then slap the ball with their tail flukes, either stunning or killing up to 10-15 herring with a successful slap. The herring are then eaten one at a time. Carousel feeding has only been documented in the Norwegian killer whale population and with some oceanic dolphin species. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke.
More specialized feeding techniques are used by various populations around the world. In Patagonia, orcas feed on southern sea lion and elephant seal pups by forcing them on to beaches, even to the extent of stranding themselves, albeit temporarily. Orcas will spy-hop to locate seals resting on ice floes, and then create a wave to wash over the floe, causing the seal to be thrown into the water where a second orca waits to kill it.
On average, the orca eats 60 kg of food each day. With this huge variety of prey, and no predators other than man, the orca is very much at the top of the food chain.
As with other dolphins, orcas are very vocal animals. They produce a variety of clicks and whistles that are used for communication and echolocation. The vocalization types vary with activity. While resting, perhaps unsurprisingly, they are much quieter, merely emitting an occasional call that is distinct from those heard when engaging in more active behaviour.
Resident pods of orcas tend to be much more vocal than transient groups. Scientists surmise that there are two main reasons for this. Firstly, resident orcas stay within the same social groups for much longer, thus developing more complicated social relationships resulting in greater vocalizations. Transient groups tend to stay together for much more fleeting amounts of time (usually just a period of hours or days) and thus communicate less. Secondly, transient orcas are much more likely to feed on marine mammals than fish-loving resident pods. Orcas hunting for mammals to eat naturally must be quieter to avoid the possibility of detection. For this reason, orcas that are hunting tend to use just a single click (called a cryptic click) for echolocation rather than the long train of clicks observed in other species.
Resident pods have regional dialects. Each pod has its own songs or sets of particular whistles and clicks that it will repeat over and over. Every member of the pod seems to know all the songs of the pod, so it is not possible to identify a single animal using voice alone, only a dialectal group. A particular song might be known by only one group or shared among several. The degree to which two groups have their songs in common appears to be a function of their genealogical closeness rather than their geographical closeness. Two groups that share a common set of ancestors but have grown apart in distance are likely to have a similar set of songs. This suggests that songs are passed from mother to child during the nursing period.
See also: Whale song
Orcas in history
Although only scientifically identified as species in 1758, the orca has been known to man since prehistoric times. The desert culture of Nazca created a Nazca line representing an orca sometime between 200 BC and AD 600.
The first description of an orca is given in Pliny the Elder's Natural History (written circa 50 BC). The aura of invincibility around the all-consuming orca was well-established by this time. Having watched the public slaughtering of a whale stranded at a harbor near Rome, Pliny writes, "Orcas, (the appearence of which no depiction can express, other than an enormous mass of savage flesh with teeth), are the enemy of [other whales]... charge and pierce them like warships ramming."
Orcas and modern man
Orcas were targeted in commercial whaling for the middle part of the twentieth century once stocks of larger species had been depleted. Commercial hunting of orcas came to an abrupt halt in 1981 with the introduction of the moratorium on all whaling. (Although from a taxonomic point of view an orca is a dolphin rather than a whale, it is sufficiently large to come under the purview of the International Whaling Commission.)
The greatest hunter of orcas was Norway which took an average of 56 animals per year from 1938 to 1981. Japan took an average of 43 animals from 1946 to 1981. (War year figures are not available but are likely to be far fewer). The Soviet Union took a few animals each year in the Antarctic, with the extraordinary exception of the 1980 season when it took 916.
Today, no country carries out a substantial hunt. Japan usually takes a few individuals each year as part of its controversial program of "scientific research." A similarly small level of subsistence whaling is carried out by Indonesia and Greenland. As well as hunting for their meat, orcas have also been killed because of their competition with fishermen. In the 1950s the U.S. Air Force, at the request of the Icelandic government, used bombers and riflemen to slaughter orcas in Icelandic waters because they competed with humans for fish. The operation was considered a great success at the time by fishermen and the Icelandic government. However, many were unconvinced that orcas were responsible for the drop in fish stocks, blaming overfishing by humans instead. This debate has led to repeated studies of North Atlantic fish stocks, with neither side in the whaling debate giving ground since that time.
The orca is also occasionally killed out of fear of its reputation. No human has ever been attacked by an orca in the wild, but sailors in Alaska shoot the animal occasionally with concern for their own lives. This fear has generally dissipated in recent years due to better education about the species, including the appearance of orcas in aquariums and other aquatic attractions.
The orca's intelligence, trainability, striking appearance, playfulness in captivity, and its sheer size have made it a popular exhibit at aquariums and other aquatic attractions such as aquatic theme parks. The first orca capture and display took place in Vancouver in 1964. Over the next 15 years around sixty or seventy orcas were taken from Pacific waters for this purpose. In the late 1970s and the first half of the 1980s, orcas were generally taken from Icelandic waters (fifty in the five years to 1985). Since that time, orcas have been successfully bred in captivity and wild specimens are considerably rarer. Orcas in captivity may develop pathologies such as dorsal fin collapse, seen in 60-90% of captive males.
There have been incidents with orcas in captivity attacking humans. In 1991, a group of orcas killed a trainer named Keltie Byrne at Sealand in Victoria, British Columbia (where employees were not allowed in the water with orcas), apparently not knowing she could not survive underwater. In 1999, at the SeaWorld park in Orlando, Florida, one of the same orcas allegedly killed a tourist who had sneaked into the orca's pool at night . (The tourist was also thought to be a victim of hypothermia.) In late July 2004, during a show at the SeaWorld park in San Antonio, Texas, an orca pushed its trainer of ten years underwater and barred the way to the rim of the pool; the trainer could only be rescued from the raging animal after several minutes.
One of the more infamous incidents involving orca aggression took place in August 1989, when, during a live show, one female whale, Kandu V (who had established herself as the dominant female) struck another whale, Corky II, imported from Marineworld California just months prior to the incident. According to reports, a loud smack was heard across the stadium. Although trainers tried to keep the show rolling, the blow severed an artery near Kandu V's jaw, and she began spouting blood. The crowd was quickly ushered out, and after a 45-minute hemorrhage, Kandu V died. Opponents of these shows see these incidents as supporting their criticism.
SeaWorld continued to be implicated in unfair practices by keeping orcas taken from the wild, and came under criticism from the Born Free Foundation over its continued captivity of the orca Corky , who they want to be returned to its family in the A5 Pod —a large pod of orcas in British Columbia, Canada  .
As late as the 1970s, orcas were depicted negatively in fiction as ravenous predators whose behavior caused heroes to interfere to help a prey animal escape. The most extreme example is the poorly received film Orca which featured the story of an orca going on a vengeful rampage after its mate is killed by humans (in an obvious attempt to copy the success of Jaws).
However, the increased research of the animal and its popularity in public venues brought about a dramatic rehabilitation of the animal's public image. The sentiment about the animal grew to more as a respected predator that poses little actual threat to humans, much as the North American wolf's image has been changed.
The movie Free Willy (1993) focused on the quest for freedom for a captive orca. The whale starring in the movie, Keiko, was originally caught in Icelandic waters. After rehabilitation at the Oregon Coast Aquarium in Newport, Oregon, he was later returned to the waters of the Nordic countries, his native habitat, but continued to be dependent on humans until his death in December 2003.
The Exxon Valdez oil spill had a particularly adverse effect on the Alaskan orca population. One pod was caught in the spill; though the pod successfully swam to clear water, eleven members of the pod (about half) died in the following days and weeks. The spill had a longer-term effect in reducing the amount of available prey, such as salmon, and has thus been responsible for a local population decline. In December 2004, scientists at the North Gulf Oceanic Society said that the pod (called the AT1 pod) now only came to seven in number, having failed to reproduce at all since the spill. The population is expected to become completely extinct. Press Telegram report on the pod
Like other animals at the highest trophic levels of the food chain, the orca is particularly susceptible to poisoning via accumulation of Polychlorinated biphenyls (PCBs) in the body. A survey of animals off the Washington coast found that PCB levels in orcas were higher than those in harbour seals in Europe (what have been sickened by the chemical). However, no direct evidence of sickness in orcas has been found. The most likely effect, if any, would be a reduced rate of reproduction.
Other environmental pressures facing orcas include extensive whale-watching which some research indicates changes whale behavior. Heavy ship noise has caused some groups of orca to change the frequencies of their songs and calls.
- Orca: The Whale Called Killer, Erich Hoyt, Camden House Publishing, ISBN 0920656250
- Killer Whale, John K.B. Ford, pp669–675 in the Encyclopedia of Marine Mammals, Academic Press, ISBN 0125513402
- National Audubon Society Guide to Marine Mammals of the World, Reeves, Stewart, Clapham and Powell. Alfred A. Knopf. ISBN 0375411410
- Kharakter vzaimootnoshenii kasatok i drugikh kitoobraznykh in Morskie mlekopitayushchie (in Russian, transliterations vary). The nature of interrelationships between Killer Whales and Other Cetaceans I.V.Shevchenko, 1975 pp173–175. (The author describes his discovery of orca cannibalism).
- Guardians of the Whales, Graeme Ellis and Bruce Obee, Whitecap Books, ISBN 1551100347
- Killer Whales, John K.B. Ford, Graeme Ellis, Kenneth C. Balcomb, UBC Press, ISBN 0774804696
- Monterey Bay Whale Watch Photos: Killer Whales Attacking Gray Whales
- Predation Behavior of Transient Killer Whales in Monterey Bay, California
- Killer Whale image archive showing orca from Arctic Norway
- Research project studying Killer whales in the Norwegian Arctic
- Research project studying Predator prey interactions, includes satellite-tagged orca in the Norwegian Arctic
- Killer Whale facts
- Pictures of orca