The Orca (Orcinus orca), commonly referred to as the Killer Whale and, less commonly, Blackfish, is the largest species of the dolphin family. They are commonly mistaken as a species of whale. They are found in all the world's oceans, from the frigid Arctic and Antarctic regions to warm, tropical seas. Some killer whale populations feed mostly on fish, including sharks, while others hunt marine mammals such as sea lions, seals, walruses and even large whales. Some killer whales even eat great white sharks.
There are up to five distinct killer whale types distinguished by geographical range, preferred prey items and physical appearance. Some of these may be separate races, subspecies or even species. Killer whales are highly social; some populations are composed of matrilineal family groups, which are the most stable of any animal species. The sophisticated social behavior, hunting techniques, and vocal behavior of killer whales have been described as manifestations of culture.
Although the killer whale is not considered to be an internationally endangered species, some local populations are considered threatened or endangered due to depletion of prey species, habitat loss, pollution by PCBs, capture for marine mammal parks, and conflicts with fisheries. In late 2007, the killer whales known as the "southern resident killer whales" were placed on the U.S. Endangered Species list. Due to the likelihood that not all killer whales belong to a single species, the IUCN currently asseses the conservation status of the killer whale as data deficient.
Wild killer whales are usually not considered a threat to humans. There have, however, been isolated reports of captive killer whales attacking , and in at least one instance, killing their handlers at marine theme parks.
Taxonomy and evolution
Orcinus orca is the sole species in the genus Orcinus, one of the many species originally described by Linnaeus in 1758 in Systema Naturae. It is one of thirty-five species in the dolphin family, which is believed to date back at least five million years. Like the Sperm Whale genus Physeter, Orcinus is currently classified as a genus with a single, abundant species, which would make the killer whale one of the oldest dolphin species.
There are at least three to five types of killer whales that are distinct enough to be considered different races, subspecies, or possibly even species. The IUCN reported in 2008, "The taxonomy of this genus is clearly in need of review, and it is likely that O. orca will be split into a number of different species or at least subspecies over the next few years." 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. The resident killer whales' diet consists primarily of fish and sometimes squid, and they live in complex and cohesive family groups. Pods possess lifelong family bonds, often living in large matrilineal groups and vocalizing in highly variable and complex dialects. Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner. They are known to visit the same areas consistently. The resident populations of British Columbia and Washington are amongst the most intensely studied marine mammals ever. Researchers have identified and named over 300 killer whales over the past 30 years.
- Transient: The diet of these killer whales 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. Pods consist of smaller groups with less persistent family bonds and vocalizing in less variable and less complex dialects. Female transients are characterized by dorsal fins that are more triangular and pointed than those of residents. The gray or white area around the dorsal fin, known as the "saddle patch," often contains some black coloring in residents. However, the saddle patches of transients are solid and uniformly gray. Transients roam widely along the coast—some individuals have been sighted in Southern Alaska and later in California.
- Offshore: These killer whales were discovered in 1988 when humpback whale researcher Jim Darling signaled to killer whale researchers Michael Bigg and Graeme Ellis that he saw killer whales in open water. These killer whales cruise the open oceans and are believed to feed primarily on schooling fish. However, because of the large presence of scarred and nicked dorsal fins resembling that of the mammal-hunting transients, the possibility that they eat mammals and sharks cannot be ruled out. They have mostly been encountered off the west coast of Vancouver Island and near the Queen Charlotte Islands. They have been seen traveling 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. Offshores appear to be shorter than the residents and the transients and females are characterized by dorsal fin tips that are continuously rounded.
Killer whale 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 killer whales in Alaska and Norway have also been observed to have resident-like social structures. Mammal-eating killer whales in Argentina and the Crozet Islands have been observed to behave more like transients. Transient and resident killer whales live in the same areas, but avoid each other. The name transient originated from the belief that these killer whales 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 killer whale types have recently been documented in the Antarctic.
- Type A looks like a "typical" killer whale, a large, black and white form with a medium-sized white eye patch, 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 killer whale. 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 Cod.
Type B and C killer whales 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 whether Type B and C killer whales are different species.
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 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. It is thought to derive from the name Spanish sailors gave the species, asesina ballenas or "asesino de la ballena" ("whale killer" in English) because Orcas would hunt and kill other whales. However, since the 1960s, Orca has steadily grown in popularity as the common name to identify the species, and both names are now used. This change was encouraged to avoid the negative connotations of "killer." 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", 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 is also similar to Orcus, a Roman god of the underworld.
They are sometimes referred to as blackfish, a name also used for other types of 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.
A common reason for the use of "orca" in favor of "killer whale" is the fact that orcas are not whales, but rather are related to dolphins.
Killer whales 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. Killer whales have a heavy and stocky body and a large dorsal fin with a dark grey "saddle patch" at the fin's rear. Antarctic killer whales may have pale grey to nearly white backs. Males typically range from 6–8 m long (19–26 ft) and weigh in excess of 6 tons. Females are smaller, generally ranging from 5–7 m (16–23 ft) and weighing about 3 to 4 tons. The largest male killer whale on record was 9.8 m (32 ft) and weighing over 10 tonnes (22,000 lb), while the largest female was 8.5 m (28 ft) and weighing 7.5 tonnes (16,500 lb). Calves at birth weigh about 180 kg (350-500 lb) and are about 2.4 m long (6–8 ft). The killer whale's large size and strength make it among the fastest marine mammals, often reaching speeds in excess of 35 kn (65 km/h). Unlike most dolphins, the pectoral fin of a killer whale 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 male's dorsal fin is more than twice the size of the female's and is more of a triangular shape—a tall, elongated isosceles triangle—whereas the dorsal fin of the female is shorter and generally more curved. Adult male killer whales 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, for example, the false killer whale or Risso's dolphin.
Individual killer whales 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 killer whales from each other. For the well-studied killer whales of the northeast Pacific, catalogues have been published with the photograph and name of each killer whale. Photo identification has enabled the local population of killer whales to be counted each year rather than estimated and has enabled great insight into killer whale lifecycles and social structures.
The Center For Whale Research in the San Juan Islands annually surveys the Southern Resident Community. These guides are available through the Whale Museum in Friday Harbor and include mugshots of each whale's dorsal fin and saddle patch to be used for identification. (http://www.whalemuseum.org/programs/orcadoption/whalelist.html)
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 18 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. Newborn mortality is very high—one survey suggested that nearly half of all calves fail to reach one year old. Calves nurse for up to two years but will start to take solid food at about twelve months. All resident killer whale pod members, including males of all ages, participate in the care of the young. Cows breed until the age of 40, meaning that on average they raise five offspring. Typically, females' life spans average 50 but may survive well into their 70-80s in exceptional cases. Males become sexually mature at the age of 15 but do not typically reproduce until age 21. Male killer whales generally do not live as long as females. In the wild, males average 30 years, with a maximum of 50–60 years in exceptional cases. However, one male, known as Old Tom, was reportedly spotted every winter between 1843 and 1932 off New South Wales, Australia. This would have made him at least 89 years old. The lifespans of captive killer whales have been known to be significantly shorter, usually less than 25 years, however there are numerous individuals in their thirties, and a couple in their 40s. In many instances, the lifespans of orcas often depend on the will of the animal.
Killer whales 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 killer whale is particularly highly concentrated in the northeast Pacific Basin, where Canada curves into Alaska as well as the Johnstone Strait area and Washington state. They are making a bigger presence in California too. There are also large populations off the coast of Iceland and off the coast of northern Norway. They are regularly sighted in Argentina and the 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 killer whale 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 70,000–80,000 in the Antarctic, 8,000 in the tropical Pacific (although tropical waters are not the killer whale's preferred environment, the sheer size of this area—19 million square kilometres—means there are thousands of killer 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.
With the rapid decline of Arctic sea ice in the Hudson Strait, the range of killer whales has now extended into the far northern waters of Canada. Through the 1990s, killer whales were sighted in western Hudson Bay at a rate of 6 per decade; sightings rose to more than 30 between 2001–2006.
White killer whales have been spotted in the northern Bering Sea and around St. Lawrence Island. Also, there have been sightings along the Russian coast. In February 2008, a white killer whale was photographed two miles (3 km) off Kanaga Volcano. The whale was a healthy, adult male about 25 to 30 feet (9.1 m) long and weighing upward of 10,000 pounds.
The migration patterns of killer whales are poorly understood. Each summer, the same resident killer whales 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. Transient pods have been sighted from southern Alaska to central California.
On some occasions, killer whales will swim into freshwater rivers. They have been documented 100 miles (160 km) up the Columbia River in the United States. They have also been found in the Fraser River in Canada and the Horikawa River in Japan.
The killer whale is an apex predator. They are sometimes called the wolves of the sea, because they hunt in pods like packs of wolves. On average, a killer whale eats 227 kg (500 lb) of food each day.
Killer whales 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 killer 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 killer whale population, despite the high overall diversity of potential killer whale prey.
Although, unlike transient killer whales, resident killer whales 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 killer whales prey on around 30 species of fish, particularly salmon (including Chinook and Coho), herring, and tuna. In New Zealand, killer whales have been observed hunting sharks (particularly mako sharks, thresher sharks and smooth hammerheads) as well as stingrays, which seem to be their favorite treat as they will go to nearly any length to get them. In one incident off the Farallon Islands, a great white shark was killed by a killer whale, which then ate the shark's nutrient-rich liver. 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 killer whale or a small group of individuals, herring are often caught using carousel feeding: the killer whales force the herring into a tight ball by releasing bursts of bubbles or flashing their white undersides. The killer whales 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.
Twenty-two cetacean species have been recorded as preyed on by killer whales, either through an examination of stomach contents, from examining scarring on the prey's body, or from observing the killer whales' feeding activity. Groups of killer whales attack even larger cetaceans such as Minke whales, Gray whales, and, very occasionally, Sperm Whales or Blue whales. Killer whales generally choose to attack whales which are young or weak. However, a group of five or more killer whales may attack healthy adult whales. Bull Sperm Whales are avoided, as they are large, powerful, and aggressive enough to kill killer whales. Bottlenose Dolphins are occasionally hunted by certain types of killer whales but they are generally avoided or in the case of some killer whales even befriended by them.
When hunting a young whale, a group chases it and its mother until they are worn out. Eventually the killer whales 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 killer whales 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 killer whales. Hunting large whales, however, takes a lot of time, usually several hours. Killer whale cannibalism has also been reported.
Other marine mammal prey species include most species of seal, sea lion and fur seal. Walruses and Sea otters are taken less frequently. Killer whales 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. In the Aleutian Islands off Alaska, Sea otters became more frequent prey for killer whales during the 1990s. This is due to the decline in population of the killer whale's preferred prey in the area; Harbor seals and Steller sea lions.
Some highly specialized hunting techniques have been observed. Off Península Valdés, Argentina, and the Crozet Islands, killer whales 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 killer whales have been observed to teach the younger ones the skills of hunting in shallow water. Off Península Valdés, adults pull seals off the shoreline for younger killer 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: killer whales spy-hop to locate Weddell seals, Ross seals, Crabeater seals and Leopard 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 killer whale waits to kill it.
Several species of birds are preyed upon, including penguins, cormorants and sea gulls. A captive killer whale in Friendship Cove discovered that it could regurgitate fish onto the surface, attracting sea gulls, and then eat them. Other killer whales then learned the behavior by example.
The day-to-day behavior of killer whales is generally divided into four activities: foraging, traveling, resting and socializing. Killer whales are generally enthusiastic in their socializing, engaging in behaviors such as breaching, spyhopping, and tail-slapping.
Killer whales often spy-hop. This behavior is when the killer whale propels itself half-way out of the water. A killer whale may do this for one of two reasons. Either the whale is looking for food, less common, the whale is seeing where it is, or where it is relative to shore.
Resident killer whales can also be seen swimming with porpoises, other dolphins, seals, and sea lions, which are common prey for transient killer whales. Resident killer whales are continually on the move, sometimes traveling 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 killer whale pods may be as much as 1300 km (800 miles) or as little as 320 km (200 miles).
Social structure of resident killer whale communities
Fish-eating killer whales 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 killer whales of both sexes live with their mothers for their entire lives. Therefore, killer whale 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. Killer whales within a pod do not interbreed; mating occurs only between members of different pods.
Resident pods have up to 50 or more members, with an average of 15 in the Northern resident community in the Pacific Northwest. Occasionally, several pods join to form superpods, sometimes with more than 150 animals. Resident pods often include subpods, which comprises one daughter or cousin that sometimes travels only with her offspring and sometimes joins 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 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 a 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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