Orca
|
? Orca Conservation status: Lower
risk
|
|||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Orca, jumping
upside-down.
|
|||||||||||||||
| Scientific classification | |||||||||||||||
|
|||||||||||||||
| Orcinus
orca Linnaeus, 1758 |
|||||||||||||||
 Orca range (in
blue)
|
|||||||||||||||
|
|
The orca (Orcinus orca)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 orca also attacks whales, in particular gray whales.
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 broad sense that all cetaceans are whales) nor a danger to humans. Aside from a boy who was charged (but not grabbed) while swimming in a bay in Alaska, there have been no confirmed attacks on humans. There have, however, been isolated reports of captive orcas attacking their handlers at marine theme parks.
A former name for the species is grampus. This is now seldom used and should not be confused with the Grampus genus (containing Risso's Dolphin).
Naming
The name "orca" (plural "orcas") was originally given to these animals by the ancient Romans, possibly borrowed from the Greek word ὄρυξ which (among other things) referred to a species of whale.
The name "killer whale" is widely used in common English. However since the 1960s "orca" has steadily grown in popularity as the common name to identify the species and both names are now used with similar frequency.
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 on the species, there has been a convergence in naming.
Furthermore, the killer in "killer whale" is often wrongly assumed to imply that the creature is a killer of humans, an attitude amplified by an unfortunate movie seeking to capitalize from the buzz from Jaws (1975). Orca: The Killer Whale (1977) starred Richard Harris and Bo Derek. It is thought this long standing and often fearful reputation can be put to rest by using the more neutral name of orca.
A pod of orcas is capable of taking down a large whale. It is commonly thought that 18th-century Spanish sailors dubbed these creatures asesina-ballenas, or "whale killer" for this reason. However, this title was improperly translated into English as "killer whale". The term became so prevalent that Spanish speakers commonly used its retranslation of ballena asesina.
There are still many, especially in the research community, who prefer the original name, believing it to be an appropriate 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 genus name "Orcinus" means "from Hell" (see Orcus) and although the name "orca" (in use since antiquity) is probably not etymologically related, the assonance might have given some people the idea that it means "whale that brings death," or "demon from hell."
It is noteworthy that the name of this species is similarly intimidating in many non-European languages. To the Haida people native to the islands of Haida Gwaii off the coast of British Columbia, the animal was known as 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 killer whale 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 killer whale 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.
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 with a dark gray "saddle patch" behind it. Males can be up to 9.5 m long (31 ft) and weigh in excess of 6 tons; females are smaller, reaching up to 8.5 m (28 ft) and a weight of about 5 tons. Calves at birth weigh about 180 kg and are about 2.4 m long (8 ft). Unlike most dolphins, the pectoral fin of an orca is large and rounded — more of a paddle than other dolphin species. At about 1.8 m (6 ft), the dorsal fin of the male is more than twice the size of the female's, and is more of a triangle shape — a tall, elongated isosceles triangle, whereas the dorsal fin of the female is shorter and shaped like a scythe. Nicks, cuts and scrapes on these fins, as well as distinctive features of each fin, help scientists identify individuals.
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. Cows breed until the age of 40, meaning that on average they raise five offspring. Typically females live to the age of fifty, but may survive well into their eighties or nineties in exceptional cases. Males become sexually mature at the age of 15, but do not typically reproduce until age 21. Males live to about 30 on average, and to 50 in exceptional cases.
Range
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 killer whale 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.
Social interaction
Fish-eating killer whales in the North Pacific have a complex system of social grouping. The basic unit is the matriline, which consists of a single female (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 traveling together. 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 form loose aggregations called pods, consisting on average of about 18 animals. Members of a pod all have the same dialect (see the section on vocal behaviour 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, three communities of fish-eating killer whales have been identified:
-
- The southern community (1 clan, 3 pods, 92 orcas as of 2005, counting Luna (L98))
- 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, some male and female offspring eventually disperse from the maternal group. 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 penises. Whether this interaction is part of play or a display of dominance is not known.
Diet
Three "types" of orcas occur of the west coast of North America: residents, transients and offshores. Resident orcas only eat fish, transients eat seals, sea lions, porpoises and dolphins as well as small whales (such as minke whales). Not enough is known about offshores to confirm their diet.
The array of species on which orcas prey is extremely diverse. Specific populations show a high degree of specialization on particular prey species. For example, some 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.
The killer whale 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. Groups of orcas will even prey upon larger whales such as minke whales, grey whales, female and juvenile sperm whales or even young blue whales. A group of killer whales 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. Large whales are typically killed by drowning.
There has also been one recorded case of probable orca cannibalism. A study carried out by V. I. Shevchenko 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 orcas were forced to cannibalism through a lack of food.
The diet of killer whales shows substantial variation among different populations. Fish-eating populations prey on 30 species of fish, particularly salmon (including chinook and coho), herring, and tuna. Basking sharks, oceanic whitetip sharks, and very occasionally even great white sharks are taken for their nutrient-rich livers. Other marine mammals, including most species of seal and sea lion, are mammal-eating 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 squids, are also targets.
Orcas use complex hunting strategies to find and subdue their prey. 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 orca population and with some oceanic dolphin species. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke.
A captive orca in Friendship Cove discovered that it could regurgitate fish onto the surface, attract sea gulls, and eat them. Other orcas then learned the behaviour by example. [1]
More specialized feeding techniques are used by various populations around the world. In Patagonia, orcas feed on southern sea lion and elephant seal pups in shallow water, 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.
Vocal Behaviour
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.
Fish-eating resident groups of killer whales in the Northeat Pacific tend to be much more vocal than transient groups living in the same waters. Scientists surmise that the main reason for this lies in the different hearing abilities of their prey. Resident killer whales feed on fish, particularly on Pacific salmon, a prey with poor underwater hearing that cannot detect killer whale calls at any significant distance. Transient killer whales on the other hand feed exclusively on marine mammals (primarily seals, sea lions, porpoises and dolphins) and occasionally on seabirds. Because all marine mammals have excellent underwater hearing, transients probably remain silent for much of the time to avoid detection by their acoustically sensitive prey. For the same reason, mammal-hunting killer whales tend to restrict their echolocation, occasionally using just a single click (called a cryptic click) rather than the long train of clicks observed in other populations.
Resident pods have group-specific dialects. Each pod has its own vocal repertoire or set of particular stereotyped underwater calls (call types). Every member of the pod seems to know all the call types of the pod, so it is not possible to identify a single animal using voice alone, only a dialectal group. A particular call type might be used by only one group or shared among several. The number of call types shared by two groups appears to be a function of their genealogical relatedness rather than their geographical distance. Two groups that share a common set of ancestors but have grown apart in distance are likely to have a similar set of call types. This suggests that calls are learned behaviour traits that are copied between related individals through vocal mimicry.
Orcas in history
Although only scientifically identified as species in 1758, the orca has been known to humans since prehistoric times. The desert culture of the 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 appearance of which no image can express, other than an enormous mass of savage flesh with teeth), are the enemy of [other whales]... they charge and pierce them like warships ramming."
Indigenous tribes in the Pacific Northwest of North America such as the Tlingit, Haida, and Tsimshian featured the orca prominently in their religion and artwork.
Orcas and modern man
Hunting
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 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 United States Air Force, at the request of the Government of Iceland, 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.
Captivity
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 snuck into the orca's pool at night [2]. (The dead tourist, who was otherwise physically unharmed, 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 a dominant female whale, Kandu V, struck a newcomer whale, Corky II, with her mouth during a live show. Corky II had been 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 under criticism from the Born Free Foundation over its continued captivity of the orca Corky II, who they want to be returned to its family in the A5 Pod—a large pod of orcas in British Columbia, Canada [3].
Popular culture
As late as the 1970s, orcas were depicted negatively in fiction as ravenous predators whose behaviour caused heroes to interfere to help a prey animal escape. The poorly received film Orca , featured the story of a male orca going on a vengeful rampage after its pregnant mate is killed by humans. Many consider this an obvious attempt to duplicate the success of Jaws, although it can also be considered to show the animals as being (perhaps unrealistically) much more human like, with intelligence and a great capacity for love and tenderness as well as vengeance.
Orca is also the name of Quint's boat in the movie 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 he died of pneumonia in December 2003.
Environmental threats
The Exxon Valdez oil spill had an adverse effect on killer whales in Prince William Sound and the Kenai Fjords region of Alaska. One resident pod was caught in the spill; though the pod successfully swam to clear water, eleven members of the pod (about half) disappeared in the following year. 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 AT1 transient population of killer whales, now only numbering 7 individuals, has failed to reproduce at all since the spill. This population is expected to go extinct. Press Telegram report on this population
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 that have been sickened by the chemical. Samples from the blubber of orcas in the Norwegian Arctic show higher levels of PCBs, pesticides and brominated flame-retardants than in Polar bears. However, no direct evidence of sickness in orcas has been found. The most likely effect, if any, would be a reduced rate of reproduction or decreased ability to fight off disease (immunodepression). On November 15, 2005 the United States government listed the Southern Resident population of killer whales as an endangered species under the Endangered Species Act (ESA) due to deterioration of the three pods which spend most of the year in Georgia and Haro Straits, as well as Puget Sound in British Columbia and Washington State.
Other environmental pressures facing killer whales include extensive whale-watching which some research indicates changes whale behaviour. Heavy ship noise can interfere with the acoustic communication and echolocation of killer whales.
Famous Orcas
- Shamu — performs along with Baby Shamu and Grandbaby Shamu at SeaWorld
- Keiko — performed in the first of the three Free Willy movies.
Media
 |
|
Other resources
- Ellis, Graeme, Bruce Obee. Guardians of the Whales, Whitecap Books. ISBN 1551100347.
- Ford, John K.B., Graeme Ellis, Kenneth C. Balcomb. Killer Whales, UBC Press. ISBN 0774804696.