Killer Whale (Orcinus orca) - Wiki
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[Photo] Transient Orcas near Unimak Island, eastern Aleutian Islands, Alaska. From http://www.afsc.noaa.gov/Quarterly/amj2005/divrptsNMML3.htm Original caption: Figure 1. Two mammal-eating "transient" killer whales photographed off the south side of Unimak Island, eastern Aleutian Islands, Alaska. Photo by Robert Pittman.
The Orca or Killer Whale (Orcinus orca), less commonly, Blackfish or Seawolf, is the largest species of the oceanic dolphin family (Delphinidae). It is found in all the world's oceans, from the frigid Arctic and Antarctic regions to warm, tropical seas.
Orcas are versatile and opportunistic predators. Some populations feed mostly on fish, and other populations hunt marine mammals, including sea lions, seals, and even large whales. There are up to five distinct Orca types, some of which may be separate subspecies or even species. Orcas are highly social; some populations are composed of matrilineal family groups which are the most stable of any animal species. The sophisticated social behaviour, hunting techniques, and vocal behaviour of Orcas have been described as manifestations of culture.
Although Orcas are not an endangered species, some local populations are considered threatened or endangered due to pollution, depletion of prey species, conflicts with fishing activities and vessels, habitat loss, and whaling. Wild Orcas are usually not considered a threat to humans. There have, however, been isolated reports of captive Orcas attacking their handlers at marine theme parks.
Taxonomy and evolution
The sole species in the genus Orcinus, the Orca was one of the many species originally described by Linnaeus in 1758 in his 18th century work, Systema Naturae. 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. Thus, paleontologists believe that the Orca is a prime candidate to have an anagenetic evolutionary history, forming descendant species from ancestral species without splitting of the lineage. If true, this would make the Orca one of the oldest dolphin species. However, it is unlikely to be as old as the family itself, which is believed to date back at least five million years.
However, there are at least three to five types of Orcas that are distinct enough to be considered different races, subspecies, or possibly even species. In the 1970s and 1980s, research off the west coast of Canada and the United States identified the following three types:
Resident: These are the most commonly sighted of the three populations in the coastal waters of the northeast Pacific, including Puget Sound. The resident Orcas' diet consists primarily of fish and sometimes squid and they live in complex and cohesive family groups known as pods. Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner. They are known to visit the same areas consistently. In British Columbia, Washington State and southern Alaska, the orcas have been amongst the most intensely studied marine mammals ever. researchers have identified over 300 orcas during 30 years,each given a letter corresponding to their pod and a number for the individual.
Transient: The diet of these Orcas consists almost exclusively of marine mammals; they do not eat fish. Transients in southern Alaska generally travel in small groups, usually of two to six animals. Unlike residents, transients may not always stay together as a family unit. Female transients are characterized by dorsal fins that are more triangular and pointed than those of residents. Transients travel on extremely unpredictable routes; they may be seen once in an area and never be seen after, or return 10 years later. This makes transients very hard to study. Transients were discovered in the 1970s when three orcas from British Columbia were captured but refused to eat any fish for 72 days. Eventually, one of the orcas died of starvation while the others accepted fish. It was then that local researchers began thinking of the existence of an other type of orca. Since then, transients have been successfully studied around the world, especially Argentina, the Crozet Islands and New Zealand.
Offshore: These Orcas cruise the open oceans and feed primarily on fish, sharks and sea turtles. They have been seen travelling in groups of up to 60 animals. Currently there is little known about the habits of this population, but they can be distinguished genetically from the residents and transients. Female offshores are characterized by dorsal fin tips that are continuously rounded. Offshores also seem smaller than the two other types. Offshores live only in open seas, hence the name, which makes them difficult to study. Offshores have been discovered of only 40 encounters and a lot of the information on them is speculation.
Orca populations in other parts of the world have not been as well-studied. However, there appears to be a correlation between a population's diet and its social behaviour. Fish-eating Orcas in Alaska and Norway have also been observed to have resident-like social structures. Mammal-eating Orcas in Argentina and the Crozet Islands have been observed to behave more like transients.
Transient and resident Orcas live in the same areas, but avoid each other. The name "transient" originated from the belief that these Orcas were outcasts from larger resident pods. Researchers later discovered that transients are not born into resident pods, or vice-versa. The evolutionary split between the two groups is believed to have begun two million years ago. Recent genetic research has found that the types have not interbred for up to 10,000 years.
Three Orca types have recently been documented in the Antarctic.
Type A looks like a "typical" Orca, living in open water and feeding mostly on Minke Whales.
Type B is smaller than Type A. It has a large white eyepatch and a patch of grey colouring on its back, called a dorsal cape. It feeds mostly on seals.
Type C is the smallest type and lives in larger groups than any other type of Orca. Its eyepatch is distinctively slanted forwards, rather than parallel to the body axis. Like Type B, it has a dorsal cape. Its only prey observed so far is the Antarctic toothfish.
Type B and C Orcas live close to the Antarctic ice pack, and diatoms in these waters may be responsible for the yellowish colouring of both types. Research is ongoing as to whether Type B and C Orcas are different species.
The name "Orca" (plural "Orcas") was originally given to these animals by the ancient Romans, possibly borrowed from the Greek word ???ρυξ which (among other things) referred to a species of whale. The term "orc" (or its variant "ork") has been used to describe a large fish, whale or sea-monster. It is now considered an obsolete equivalent for "Orca."
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. 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.
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 meant "whale that brings death," or "demon from hell." The name of this species is similarly intimidating in many other languages, including Finnish, Dutch, German, Haida, Japanese and Chinese.
They are sometimes referred to as blackfish, a group including pilot whales, pygmy and false killer whales, and melon-headed whales. A former name for the species is grampus. This is now seldom used and should not be confused with the Grampus genus, whose only member is Risso's Dolphin.
Orcas are distinctively marked, with a black back, white chest and sides, and a white patch above and behind the eye. Calves are born with a yellowish or orange tint, which fades to white. Orcas have a heavy and stocky body and a large dorsal fin with a dark grey "saddle patch" at the fin's rear. Males normally grow from 6.5-8 m long (20-25 ft) and weigh in excess of 6 tonnes; it has been reported that especially large males have reached nearer 8 tonnes. Females are smaller, growing from 5.7-7m (18-22 ft) and a weight of about 5 tonnes. The longest Orca ever recorded was a male off the coast of Japan, measuring 9.8 m (32 ft). Calves at birth weigh about 180 kg and are about 2.4 m long (8 ft). The Orca's large size and strength make them the fastest marine mammals, often reaching speeds in excess of 56 km/h (35mph).
Unlike most dolphins, the pectoral fin of an Orca is large and rounded ??? more of a paddle than other dolphin species. Males have significantly larger pectoral fins than females. 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 generally more curved.
Adult male Orcas are very distinctive and are unlikely to be confused with any other sea creature. When seen from a distance in temperate waters, adult females and juveniles can be confused with various other species, such as the False Killer Whale or Risso's Dolphin.
Individual Orcas can be identified from a good photograph of the animal's dorsal fin and saddle patch, taken when it surfaces. Variations such as nicks, scratches, and tears on the dorsal fin, and the pattern of white or grey in the saddle patch, are sufficient to distinguish Orcas from each other. For the well-studied Orcas of the northeast Pacific, catalogues have been published with the photograph and name of each Orca. Photo-identification has enabled the local population of Orcas to be counted each year rather than estimated, and has enabled great insight into Orca lifecycles and social structures.
Females become mature at around 15 years of age. 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 analyzed resident pods, birth occurs at any time of year, with the most popular months being those in winter. Newborn 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. All resident Orca pod members, including males of all ages, participate in the care of young whales.
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 45 on average, and up to 90 in exceptional cases. The lifespans of captive Orcas are significantly shorter, usually less than 25 years.
Orcas are found in all oceans and most seas, including (unusually for cetaceans) the Mediterranean and Arabian seas. However, they prefer cooler temperate and polar regions. Although sometimes spotted in deep water, coastal areas are generally preferred 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 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. Sightings are rare in Indonesian and Philippine waters. 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 kilometers ??? means there are thousands of Orcas), up to 2,000 off Japan, 1,500 off the cooler north-east Pacific and 1,500 off Norway. Adding very rough estimates for unsurveyed areas, the total population could be around 100,000.
With the rapid decline of Arctic sea ice in the Hudson Strait, the range of Orcas has now extended into the far northern waters of Canada. Through the 1990s, Orcas were sighted in western Hudson Bay at a rate of six per decade; sightings rose to more than 30 between 2001???2006.
The migration patterns of Orcas are poorly understood. Each summer, the same resident Orcas appear off the coasts of British Columbia and Washington State. After decades of research, it is still unknown where these animals go for the rest of the year.
The Orca is an apex predator. They are sometimes called the wolves of the sea because they hunt in packs like wolves. On average, an Orca eats 227 kg (500 lb) of food each day.
Orcas prey on a diverse array of species. However, specific populations show a high degree of specialization on particular prey species. For example, some populations in the Norwegian and Greenland sea specialise in herring and follow that fish's migratory path to the Norwegian coast each autumn. Other populations in the area prey on seals. In field observations of the resident whales of the northeast Pacific, salmon accounted for 96% of animals' diet, with 65% of the salmon being the large, fatty Chinook. They have been observed to swim through schools of the smaller salmon species without attacking any of them. Depletion of specific prey species in an area is therefore cause for concern for the local Orca population, despite the high overall diversity of potential Orca prey.
Although resident Orcas have never been observed to eat other marine mammals, they are known to occasionally harass and kill porpoises and seals for no apparent reason.
Fish and other cold-blooded prey
Fish-eating Orcas prey on 30 species of fish, particularly salmon (including Chinook and Coho), herring, and tuna, as well as basking sharks, Oceanic whitetip sharks and Smooth hammerheads. In one incident, off the Farallon Islands a subadult Great white shark was killed by a mother orca protecting her calf. The calf then ate the shark's nutrient-rich liver. In New Zealand killer whales have been observed hunting stingrays as well. Cephalopods, such as octopuses and a wide range of squids, and reptiles, such as sea turtles, are also targets.
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 undersides. 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.
Twenty-two cetacean species have been recorded as preyed on by Orcas, either through an examination of stomach contents, examining scarring on the prey's body, or from observing the Orcas' feeding activity. Groups of Orcas attack even larger cetaceans such as Minke Whales, Gray Whales, and very occasionally Sperm Whales or Blue Whales. Orcas generally choose to attack whales which are young or weak. However, a group of five or more Orcas may attack healthy adult whales. Bull Sperm Whales are generally avoided, as they are too large, powerful, and aggressive to be considered a prey item.
When hunting a young whale, a group chases it and its mother until they are worn out. Eventually the Orcas manage to separate the pair and surround the young whale, preventing it from returning to the surface to breathe. Whales are typically drowned in this manner. Pods of female Sperm Whales can sometimes protect themselves against a group of Orcas by forming a protective circle around their calves with their flukes facing outwards. This formation allows them to use their powerful flukes to repel the Orcas. Hunting large whales, however takes a lot of time, usually several hours. Orca cannibalism has also been reported.
Other marine mammals prey species include most species of seal and sea lion. Walruses and Sea otters are taken less frequently and Polar bears are rarely taken. Orcas often use complex hunting strategies to find and subdue their prey. Sea lions are killed by head-butting or by being slapped and stunned by a tail fluke. They occasionally throw seals through the air in order to stun and kill them. Often, to avoid injury, they disable their prey before killing and eating it. This may involve throwing it in the air, slapping it with their tails, ramming it, or breaching and landing on it.
Some highly specialized hunting techniques have been observed. Off Pen??nsula Vald??s, Argentina and the Crozet Islands, Orcas feed on South American sea lions and Southern elephant seals in shallow water; even beaching themselves temporarily. Beaching, usually fatal to whales, is not an instinctive behaviour. Adult Orcas have been observed to teach the younger whales the skills of hunting in shallow water. Off Pen??nsula Vald??s, adults pull seals off the shoreline for younger whales to recapture. Off the Crozet Islands, mothers have been seen pushing their calves onto the beach, waiting to pull the youngster back if needed.
Another technique for capturing seals is known as wave-hunting: Orcas spy-hop to locate seals resting on ice floes, and then create waves by swimming together in groups to wash over the floe. This causes the seal to be thrown into the water where another Orca waits to kill it. This behaviour has only been recorded a few times and it is not known how often it occurs. The most recent recorded instance in April 2006 ended with the group of Orcas actually returning the seal to the ice floe after they had shown the younger animals how to properly perform the technique.
Orcas have also been observed preying on terrestrial mammals, such as deer and moose, swimming between islands off the northwest coast of North America.
Several species of bird are preyed upon, including penguins, cormorants and sea gulls. A captive Orca in Friendship Cove discovered that it could regurgitate fish onto the surface, attracting sea gulls, and then eat them. Other Orcas then learned the behavior by example.
The day-to-day behaviour of Orcas is generally divided into four activities: foraging, travelling, resting and socializing. Orcas are generally enthusiastic in their socializing, engaging in behaviours such as breaching, spyhopping, and tail-slapping.
Resident Orcas can also be seen swimming with porpoises, other dolphins, seals, and sea lions, which are common prey for transient Orcas. Resident Orcas are continually on the move, sometimes travelling as much as 160 km (100 miles) in a day, but may be seen in a general area for a month or more. Range for Resident Orca pods may be as much as 1300 km (800 miles) or as little as 320 km (200 miles).
Social structure of Resident Orca communities
Fish-eating Orcas in the North Pacific have a complex but extremely stable system of social grouping. Unlike any other mammal species whose social structure is known, Resident Orcas of both genders live with their mothers for their entire lives. Therefore, Orca societies are based around matrilines consisting 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 average size of a matriline is nine animals.
Because females can live for up to ninety years, it is not uncommon for four or even five generations to travel together. These matrilineal groups are highly stable. Individuals split off from their matrilineal group only 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.
Closely-related matrilines form loose aggregations called pods, consisting on average of about 18 animals. All members of a pod use a similar set of calls, known as a dialect. Unlike matrilines, pods may split apart for days or weeks at a time in order to forage. Orcas within a pod do not interbreed; mating occurs only between members of different pods.
Resident pods have up to 50 or more members. Occasionally, several pods join to form "superpods," sometimes with more than 150 animals. Resident pods often include subpod which comprises one daughter or cousin that sometimes travels only with her offspring and sometimes join the rest of the pod.
The next level of grouping is the clan. A clan consists of 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 observed 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 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.
Transient 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.
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