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Template:Taxobox end The Orca (Orcinus orca) is the largest member of the dolphin family. It is the second-most widely distributed mammal on Earth after humans, and is found in all the world's oceans. It 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 Orca is also commonly known as the Killer Whale and sometimes as the Great Killer Whale. This name reflects the animal's reputation as a magnificent and fearsome creature of the sea that dates back to Pliny the Elder. These days it is recognised that the "whale" is, from a taxonomic perspective, a dolphin and moreover does not represent a danger to humans - no attack on a human by an Orca in wildlife has ever been recorded.
Naming
Since the 1960s Orca has steadily grown in popularity as the common name used to identify the species and is now more popular than the traditional name, Killer Whale, amongst those in the field. However the latter is still widely used by the general public.
There are several reasons for the change. Firstly having the word "whale" in the name of a species that is really a dolphin is liable to cause needless confusion. Secondly the species is called Orca in most other European languages and, as there has been a steady increase in the amount of (cross-border) research into the species, there has been a convergence in naming.
However political correctness has also played a role in the name change. 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 eighteenth 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 (just not humans). These supporters of the original name point out that the naming heritage is not limited to Spanish sailors. Indeed the scientific name itself is Latin for "a whale that brings death". To the Haida tribes of British Columbia the animal was called skana or "killing demon". The Aleuts of Alaska call it polossatik or "the feared one". Japanese call them Shachi, believed to come from ancient words meaning "a fish that helps fishermen by herding fish, bringing good catch".
Finally, another name is Grampus. This is now seldom-used.
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, abudant species with no immediate relatives for 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 descendent 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 the family itself - which is known to date back at least five million years.
Physical characteristics
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 9.5 metres long (a little over 31 feet) and weigh in excess of 6 tons; females are smaller, reaching 8.5 metres (about 28 feet) at most and a weight of about 5 tons. Calves at birth weight about 180 kg and are about 2.4 metres 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 Orca are very distinctive and are unlikely to be confused with any other sea creature. In temperate waters females and juveniles could be confused with various other species, such as the False Killer Whale or Risso's Dolphin, when seen from a distance.
Most life history data about Orca has been obtained from long-term surveys of the population off the coast off British Columbia and Washington and by monitoring captive whales. The completeness of the study and highly structured nature of the pods in this population mean that 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 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 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 upto 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.
Range and distribution
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. However cooler temperate and polar regions are prefered. Although sometimes spotted in deep water, coastal areas are generally prefered to pelagic environments.
The Orca is particularly highly concentrated in the North-east 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. 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 prefered environment, the sheer size of this area - 19million square kilometres - means there are thousands of whales), up to 2,000 off Japan, 1,500 off the cooler north-east Pacific and 500 off Norway. Adding very rough estimates for unsurveyed areas the total population could be around 100,000.
Social behaviour
Orca have a complex system of social grouping. The most basic unit is the matriline. A matriline 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 whale living in the same line. These matrilineal groups are highly stable over many years. Individuals will only split off from their matrilineal group for a few hours at a time at most 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 north-east Pacific waters is nine animals.
Matrilines tend to congregrate 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. Unlikely matrilines, pods will split apart for days or weeks at a time in order to carry out foraging before joining back together. The average pod size is 18 animals. 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 and so pods from different clans are often recorded travelling 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 imposed by humans 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 a discernible familial or vocal patterns.
In the northeast Pacific there have been three communities identified:
- The southern community (1 clan, 3 pods, 83 orca as of 2000)
- The northern community (3 clans, 16 pods, 214 orca as of 2000)
- The south Alaskan community (2 clans, 11 pods, 211 orca as of 2000)
In should be emphasised that these hierarcheries 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. Transient groups however still have a looser connection defined by their dialect.
The day-to-day behaviour of Orca is generally divided into four activities - foraging, travelling, resting and socializing. Orca 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 penises. Whether this is interaction is part of play or a display of dominance is not known.
Diet
The array of species on which Orca prey is extremely diverse. Specific populations tend to specialise 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. This diversification of feeding amongst overlapping species is unique to Orca amongst mammals.
The Orca is the only cetacean species to regularly prey on other cetaceans, and this is the reason for its other common name Killer Whales. 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 taking place. Pods of Orca will even take larger whales such as Fin Whales, Minke Whales, Gray Whales, or even young Blue Whales. A group of Orca take a young Blue Whale by chasing it and its mother through the sea, wearing them out. Eventually the Orca 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 Orca are free to feed on it.
There has also been one recorded case of probable Orca cannibalism. A survey carried out by V. I. Shevenko in the temperate areas of the South Pacific in 1975 recorded two male Orca whose stomach contained the remains of other Orca. Of the 30 Orca captured and examined in this survey, 11 had empty stomachs - an unusually high percentage that indicates the Orca were forced to cannabalism through a lack of food.
More commonly Orca prey on thirty species of fish, particularly salmon, herring, tuna, chinook and coho. Basking Sharks, Oceanic Whitetip Sharks 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 sealion, 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 octopuses and a wide range of squid, are also targets.
Orca 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. Whilst salmon are usually hunted by a single or small group of individuals, herring are often caught using carousel feeding. That is, the Orca force the herring into a tight ball by releasing walls of bubbles or flashing their white underside. The Orca then lunge up through the ball, eating several fish in one swoop. Sealions 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, Orca feed on Southern Sea Lion and Elephant Seal pups by forcing them on to beaches, even to the extent of stranding themselves, albeit temporarily. Orca 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 60kg of food a 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.
Song
As with other dolphins, Orca are very vocal animals. They produce a variety of clicks and whistles that are used for communication and echolocation. The type of noises made vary with activity. Whilst resting, perhaps unsurprisingly, they are much quieter, just emitting an occasional call that is distinct from those heard when engaging in more active behaviour.
Resident pods of Orca tend to be much more vocal than transient groups. Scientists surmise that there are two main reasons for this. Firstly resident Orca 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 Orca are much more likely to feed on marine mammals than fish-loving resident pods. Orca hunting for mammals to eat naturally must be quieter to avoid the possibility of detection. For this reason hunting Orca tend to use just a single click (called a "cryptic click") for echolocation rather than the long train of clicks observed in other species.
An interesting feature of resident pods is the existence of 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. Thus it is not possible to identify a single animal using voice alone; only a dialetic group. A particular song might be known by only one group, or shared amongst several. The degree to which to two groups have their songs in common appears to be a function of their genealogical closeness rather than their geographical closeness. Thus two groups that share a common set of ancestors but have not 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
Orca in history
Although only scientifically identified as species in 1758, the Orca has been known to man since time immemorial. There are two particularly early records about Orca. In the centuries 200BC - 1BC, the Nazca tribes of Peru were known to paint Orca designs on their icons as a symbol of power and coverage. They also built temples to Orca deities.
The first description of an Orca is given in Pliny the Elder's Natural History (written c.50BC). 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 harbour near Rome, Pliny writes "A killer whale cannot be properly depicted or described except as an enormous mass of flesh armed with savage teeth... the enemy of other whales charge and pierce them like warships ramming."
Orca and modern man
Orca were targeted in commercial whaling for the middle part of the twentieth century once stocks or larger species had been depleted. Commercial hunting of Orca came to an abrupt halt in 1981 with the introduction of the morartorium 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 Orca 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 in the Antarctic, with the extraordinary exception of the 1980 season where it took 916.
Today, no country carries out a substantial hunt. Japan usually takes a few individuals each year as part of its controverserial programme of scientific research. A similarly small of subsistence whaling is carried out by Indonesia and Greenland. As well as hunting for their meat, Orca 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 Orca 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 Orca were responsibile for the drop in fish stocks - blaming instead overfishing by humans. 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. The species other common name - Killer Whale - and impressive rows of sharp teeth gave rise to a fearsome reputation. In fact no human has ever been attacked by an Orca in wildlife. Nevertheless fearful sailors in Alaska continue to resort to shooting the animal occasionally out of fear for their lives. This fear has generally dissipated in recent years, due to better education about the species. Part of this education has been the appearance of Orca in aquariums and other aquatic attractions. The Orca's intelligence, trainability, striking appearance, playfulness in captivity and its sheer size have made it amongst the popular exhibits at such places. The first Orca capture and display took place in Vancouver in 1964. Over the next 15 years around 60-70 Orca were taken from Pacific waters for this purpose. In the late 70s and the first half of the 80s Orca were generally taken from Icelandic waters (50 in the five years to 1985). Since that time Orca have been sucessful bred in captivity and wild specimens are considerably rarer. Orca in captivity may develop pathologies such as dorsal fin collapse, seen in 60-90% of captive males.
It must be noted that there have been incidents with Orcas in captivity attacking humans. A group of orcas killed a trainer in a Canadian aquarium, and in 1999 an orca killed a tourist who had sneaked into his pool at night. In late July 2004, an Orca attacked its trainer in a "Sea World" park in Texas. During a show, the animal pushed its trainer under water and barred the way to the rim of the pool. The trainer, who could only be rescued from the raging animal by helpers after several minutes, already worked for ten years with this Orca. In another Sea World park, one orca killed another. Opponents of these shows see these incidents as supporting their criticisms.
The movie Free Willy (1993) focused on the quest for freedom for a captive orca and his human well-wishers. 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.
Other environmental pressures facing Orca include extensive whale-watching which some research indicates changes whale behaviour. Heavy ship noise and "seal scarers" - small noise-emitting devices placed in coastal areas to scare seals away from salmon farms have caused some groups of Orca to change the frequencies of their "songs" and calls.
The Exxon Valdez oil spill had a a particularly adverse effect on the Alaskan population. One pod was caught in the spill. Although the pod successfully swam through the oil to clear water, 14 of the pod (about half) died in the following days and weeks. The spill had a longer-term effect in reducing the amount of prey, such as salmon, available and thus was responisble for a local population decline.
Like other animals at the highest trophic levels of the food chain, the Orca is particularly susceptible to poisoning via accumulation of PCBs in the body. A survey of animals off the Washington coast found that PCB levels in Orca were higher than those in Harbour Seals in Europe that have been proved to be made sick by the chemicals. However direct evidence of sickness in Orca has been found. The most likely effect, if any, would be a reduced rate of reproduction.
References
- 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).
External links
- 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