Killer Whale

The killer whale (Orcinus orca), commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas. Killer whales as a species have seal a diverse diet, although individual populations often specialize in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as sea lions, seals, walruses and even large whales. Killer whales are regarded as apex predators, lacking natural predators and preying on even large sharks.

Killer whales are highly social; some populations are composed of matrilineal family groups which are the most stable of any animal species.[5] Their sophisticated hunting techniques and vocal behaviors, which are often specific to a particular group and passed across generations, have been described as manifestations of culture.[6]

The IUCN currently assesses the orca's conservation status as data deficient because of the likelihood that one or more killer whale types are separate species. Some local populations are considered threatened or endangered due to prey depletion, habitat loss, pollution (by PCBs), capture for marine mammal parks, and conflicts with fisheries. In late 2005, the killer whales known as the "southern resident killer whales" were placed on the U.S. Endangered Species list.

Wild killer whales are not considered a threat to humans,[7] although there have been cases of captives killing or injuring their handlers at marine theme parks. Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers.

Taxonomy and evolution
Orcinus orca is the only recognized extant species in the genus Orcinus, one of many animal species originally described by Linnaeus in 1758 in Systema Naturae.[8] Konrad Gessner wrote the first scientific description of a killer whale in his "Fish book" of 1558, based on examination of a dead stranded animal in the Bay of Greifswald that had attracted a great deal of local interest.[9]

The killer whale is one of 35 species in the oceanic dolphin family, which first appeared about 11 million years ago. The killer whale lineage probably branched off shortly thereafter.[7] Although it has morphological similarities with the pygmy killer whale, the false killer whale and the pilot whales, its closest extant relative is the Irrawaddy dolphin.[10]

Common names
English-speaking scientists most often use the term killer whale,[11] although the term orca is increasingly used. Killer whale advocates point out that it has a long heritage. Indeed, the genus name Orcinus means "of the kingdom of the dead",[11] or "belonging to Orcus."[12] Ancient Romans originally applied orca (plural orcae) to these animals, possibly borrowing it from the Greek ὄρυξ, which referred (among other things) to a whale species. Since the 1960s, orca has steadily grown in popularity; both names are now used. The term orca is preferred by some to avoid the negative connotations of "killer",[13] and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.[14]

They are sometimes referred to as blackfish, a name used for some whale species as well. Grampus is a former name for the species, but is now seldom used. This meaning of grampus should not be confused with the Grampus genus, whose only member is Risso's Dolphin.[15]

Types
There are three to five types of killer whales that may be distinct enough to be considered different races,[16] subspecies, or possibly even species.[17] 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."[2] In the 1970s and 1980s, research off the west coast of Canada and the United States identified the following three types: Transients and residents live in the same areas, but avoid each other.<sup class="reference" id="cite_ref-23">[24] The name "transient" originated from the belief that these killer whales were outcasts from larger resident pods. Researchers later discovered 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.<sup class="reference" id="cite_ref-24">[25] Genetic data indicates that the types have not interbred for up to 10,000 years.<sup class="reference" id="cite_ref-25">[26]
 * Resident: These are the most commonly sighted of the three populations in the coastal waters of the northeast Pacific. Residents' diet consists primarily of fish and sometimes squid, and they live in complex and cohesive family groups called pods.<sup class="reference" id="cite_ref-17">[18] Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner.<sup class="reference" id="cite_ref-carwardine4047_18-0">[19] They visit the same areas consistently. British Columbia and Washington resident populations are amongst the most-intensively studied marine mammals. Researchers have identified and named over 300 killer whales over the past 30 years.<sup class="reference" id="cite_ref-19">[20]
 * Transient: The diet of these whales consists almost exclusively of marine mammals; they do not eat fish.<sup class="reference" id="cite_ref-carwardine4047_18-1">[19] Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents. Transients vocalize in less variable and less complex dialects. Female transients are characterized by more triangular and pointed dorsal fins than those of residents.<sup class="reference" id="cite_ref-carwardine4047_18-2">[19] The gray or white area around the dorsal fin, known as the "saddle patch", often contains some black colouring in residents. However, the saddle patches of transients are solid and uniformly gray.<sup class="reference" id="cite_ref-carwardine4047_18-3">[19] Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California.<sup class="reference" id="cite_ref-20">[21]
 * Offshore: A third population of killer whales in the northeast Pacific was discovered in 1988, when humpback whale researcher Jim Darling observed them in open water. As their name suggests, they travel far from shore and feed primarily on schooling fish.<sup class="reference" id="cite_ref-21">[22] However, because of the large, scarred and nicked dorsal fins resembling those of mammal-hunting transients, they may also eat mammals and sharks. They have mostly been encountered off the west coast of Vancouver Island and near the Queen Charlotte Islands. Offshores typically congregate in groups of 20–75, with occasional sightings of larger groups of up to 200.<sup class="reference" id="cite_ref-noaa_22-0">[23] Currently, little is known about their habits, but they are genetically distinct from residents and transients. Offshores appear to be smaller than the others, and females are characterized by dorsal fin tips that are continuously rounded.<sup class="reference" id="cite_ref-carwardine4047_18-4">[19]

Other populations have not been as well studied, although specialized fish-eating and mammal-eating killer whales have been distinguished elsewhere.<sup class="reference" id="cite_ref-Jefferson_et_al_1991_26-0">[27] Separate populations of fish-eating and mammal-eating killer whales have been identified around the United Kingdom.<sup class="reference" id="cite_ref-27">[28] <sup class="reference" id="cite_ref-28">[29] Fish-eating killer whales in Alaska and Norway have resident-like social structures, while mammal-eating killer whales in Argentina and the Crozet Islands behave more like transients.<sup class="reference" id="cite_ref-29">[30]

Three types have been documented in the Antarctic. Two dwarf species, named Orcinus nanus and Orcinus glacialis, were described during the 1980s by Soviet researchers, but most cetacean researchers are skeptical about their status, and it is difficult to link these directly to the types described below.<sup class="reference" id="cite_ref-Pitman2003_16-1">[17] Types B and C live close to the ice pack, and diatoms in these waters may be responsible for the yellowish coloring of both types.<sup class="reference" id="cite_ref-Pitman2003_16-5">[17] <sup class="reference" id="cite_ref-33">[34] Mitochondrial DNA sequences support the theory that these are separate species that have recently diverged.<sup class="reference" id="cite_ref-34">[35] More recently, complete mitochondrial sequencing indicates that the two Antarctic groups that eat seals and fish should be recognized as distinct species, as should the North Pacific transients, leaving the others as subspecies pending additional data.<sup class="reference" id="cite_ref-35">[36]
 * 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.<sup class="reference" id="cite_ref-Pitman2003_16-2">[17]
 * Type B is smaller than Type A. It has a large white eye patch. Most of the dark parts of its body are medium gray instead of black, although it has a dark gray patch called a "dorsal cape"<sup class="reference" id="cite_ref-30">[31] stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals.<sup class="reference" id="cite_ref-Pitman2003_16-3">[17]
 * Type C is the smallest type and lives in larger groups than the others. Its eye patch is distinctively slanted forwards, rather than parallel to the body axis. Like Type B, it is primarily white and medium gray, with a dark gray dorsal cape and yellow-tinged patches. Its only observed prey is the Antarctic Cod.<sup class="reference" id="cite_ref-Pitman2003_16-4">[17]
 * Type D was identified based on photographs of a 1955 mass stranding in New Zealand and six at-sea sightings since 2004. Immediately recognizable by its extremely small white eye patch, shorter than usual dorsal fin that curves back, and bulbous head (similar to a pilot whale). Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. And although nothing is known about the Type D diet, it is suspected to include fish because groups have been photographed around longline vessels where they reportedly depredate Patagonian toothfish (Dissostichus eleginoides).<sup class="reference" id="cite_ref-31">[32] <sup class="reference" id="cite_ref-32">[33]

Research is ongoing into the genetic relationships among killer whale types, and whether the types that have been identified represent deep evolutionary trends. For example, it was long thought that mammal-eating killer whales were likely to be closely related to other mammal-eating killer whales from different regions, but genetic testing refuted this hypothesis.<sup class="reference" id="cite_ref-Schrope_36-0">[37]

Description
Killer whales distinctively bear 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 robust body (more so than other dolphins)<sup class="reference" id="cite_ref-37">[38] and a large dorsal fin up to 2 metres (6.6 ft) tall. Behind the fin, they have a dark grey "saddle patch" across the back. Antarctic killer whales may have pale grey to nearly white backs. Adult killer whales are very distinctive and are not usually confused with any other sea creature.<sup class="reference" id="cite_ref-38">[39] When seen from a distance, juveniles can be confused with other cetacean species such as the false killer whale or Risso's dolphin.

Males typically range from 6 to 8 metres (20–26 ft) long and weigh in excess of 6 tonnes (5.9 LT; 6.6 ST).<sup class="reference" id="cite_ref-Baird_39-0">[40] Females are smaller, generally ranging from 5 to 7 metres (16–23 ft) and weighing about 3 to 4 tonnes (3.0 to 3.9 LT; 3.3 to 4.4 ST).<sup class="reference" id="cite_ref-Baird_39-1">[40] The largest male killer whale on record was 9.8 metres (32 ft), weighing over 10 tonnes (9.8 LT; 11 ST), while the largest female was 8.5 metres (28 ft), weighing 7.5 tonnes (7.4 LT; 8.3 ST).<sup class="reference" id="cite_ref-40">[41] Calves at birth weigh about 180 kilograms (397 lb) and are about 2.4 metres (7.9 ft) long.<sup class="reference" id="cite_ref-41">[42] <sup class="reference" id="cite_ref-42">[43] The killer whale's large size and strength make it among the fastest marine mammals, able to reach speeds in excess of 30 knots (56 km/h).<sup class="reference" id="cite_ref-43">[44]

Killer whale pectoral fins are large and rounded, resembling paddles. Males have significantly larger pectoral fins than females. At about 1.8 metres (5.9 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 hers is shorter and more curved.<sup class="reference" id="cite_ref-44">[45] Males and females also have different patterns of black and white skin in the genital area.<sup class="reference" id="cite_ref-45">[46]

Individual killer whales can often be identified from the dorsal fin and saddle patch. Variations such as nicks, scratches, and tears on the dorsal fin and the pattern of white or grey in the saddle patch are unique. Published directories contain identifying photographs and names for hundreds of North Pacific animals. Photo identification has enabled the local population of killer whales to be counted each year rather than estimated and has enabled great insight into lifecycles and social structures.<sup class="reference" id="cite_ref-46">[47]

White killer whales occur sporadically among normal killer whales, but are rare. They have been spotted in the northern Bering Sea and around St. Lawrence Island, and near the Russian coast.<sup class="Template-Fact" style="white-space: nowrap;" title="This claim needs references to reliable sources from May 2010">[citation needed] In February 2008, a white killer whale was photographed 2 miles (3.2 km) off Kanaga Volcano.<sup class="reference" id="cite_ref-47">[48] <sup class="reference" id="cite_ref-48">[49]

Killer whales have good eyesight above and below the water, excellent hearing, and a good sense of touch. They have exceptionally sophisticated echolocation abilities, detecting the location and characteristics of prey and other objects in their environment by emitting clicks and listening for echoes.<sup class="reference" id="cite_ref-49">[50]

Life cycle
Female killer whales mature at around age 15. They then have periods of polyestrous cycling with non-cycling periods of between 3 and 16 months. Gestation varies from 15 to 18 months. Mothers calve, with usually a single offspring, about once every 5 years. In resident pods, birth occurs at any time of year, although winter is the most popular. Mortality is extremely high during the first six to seven months of life, when 37–50% of all calves die.<sup class="reference" id="cite_ref-50">[51] Weaning begins at about 12 months and completes by the age of two. According to observations in several regions, all male and female killer whale pod members participate in the care of the young.<sup class="reference" id="cite_ref-Heimlich_and_Boran_2001.2C_p._35_51-0">[52] Killer Whales and Pilot whales are the only species in which the females go through menopause and live for decades after they have finished breeding.<sup class="reference" id="cite_ref-52">[53]

Females breed until age 40, meaning that on average they raise five offspring. The lifespan of wild females averages 50 years, with a maximum of 80–90 years.<sup class="reference" id="cite_ref-Carwardine.2C_p._26_53-0">[54] Males sexually mature at the age of 15 but do not typically reproduce until age 21. Wild males live around 29 years on average, with a maximum of 50–60 years.<sup class="reference" id="cite_ref-Carwardine.2C_p._26_53-1">[54] One male, known as Old Tom, was reportedly spotted every winter between the 1840s and 1930 off New South Wales, Australia. This would have made him up to 90 years old. Examination of his teeth indicated he died around age 35,<sup class="reference" id="cite_ref-54">[55] but this method of age determination is now believed to be inaccurate for older animals.<sup class="reference" id="cite_ref-55">[56] One male well known to researchers in the Pacific Northwest called Ruffles (J1) is estimated to have been born in 1951, making him 58 years old in 2009.<sup class="reference" id="cite_ref-56">[57] Captive killer whale lifespans are typically significantly shorter, usually less than 25 years; however, numerous individuals are alive in their thirties, and a few have reached their 40s. In many instances, the lifespans of killer whales depend on the will of the animal.<sup class="reference" id="cite_ref-Hoyt_57-0">[58] <sup class="reference" id="cite_ref-58">[59]

Range and habitat
Killer whales are found in all oceans and most seas. Due to their enormous range, numbers and density, distributional estimates are difficult to compare,<sup class="reference" id="cite_ref-Forney2007_59-0">[60] but they clearly prefer higher latitudes and coastal areas over pelagic environments.<sup class="reference" id="cite_ref-60">[61]

Systematic surveys indicate the highest densities of killer whales (>0.40 individuals per km²) in the northeast Atlantic around the Norwegian coast, in the north Pacific along the Aleutian Islands, the Gulf of Alaska and in the Southern Ocean off much of the coast of Antarctica.<sup class="reference" id="cite_ref-Forney2007_59-1">[60] They are considered "common" (0.20–0.40 individuals per 100 km²) in the eastern Pacific along the coasts of British Columbia, Washington and Oregon, in the North Atlantic Ocean around Iceland and the Faroe Islands. High densities have also been reported but not quantified in the western North Pacific around the Sea of Japan, Sea of Okhotsk, Kuril Islands, Kamchatka and the Commander Islands and in the southern hemisphere off the coasts of South Australia, Patagonia, off the coast of southern Brazil and the tip of southern Africa. They are reported as seasonally common in the Canadian Arctic, including Baffin Bay between Greenland and Nunavut, and around Tasmania and Macquarie Island.<sup class="reference" id="cite_ref-Forney2007_59-2">[60] Information for offshore regions and tropical waters is more scarce, but widespread, if not frequent, sightings indicate that the killer whale can survive in most water temperatures. There have been sightings, for example, in the Mediterranean, the Arabian Sea, the Gulf of Mexico and the Indian Ocean around the Seychelles.<sup class="reference" id="cite_ref-Forney2007_59-3">[60]

Probably the largest population lives in Antarctic waters, where they range up to the edge of the pack ice and are believed to venture into the denser pack ice, finding open leads much like beluga whales in the Arctic. In contrast, killer whales are seasonal summer visitors to Arctic waters, where they do not approach the ice pack. With the rapid Arctic sea ice decline in the Hudson Strait, their range now extends deep into the northwest Atlantic.<sup class="reference" id="cite_ref-61">[62]

Migration patterns are poorly understood. Each summer, the same individuals appear off the coasts of British Columbia and Washington State. Despite decades of research, where these animals go for the rest of the year remains unknown. Transient pods have been sighted from southern Alaska to central California.<sup class="reference" id="cite_ref-62">[63] Resident killer whales sometimes travel as much as 160 kilometres (100 mi) in a day, but may be seen in a general area for a month or more. Resident killer whale pod ranges vary from 320 to 1,300 kilometres (200 to 810 mi).

Occasionally, killer whales swim into freshwater rivers. They have been documented 100 miles (160 km) up the Columbia River in the United States.<sup class="reference" id="cite_ref-Baird_p10_63-0">[64] <sup class="reference" id="cite_ref-64">[65] They have also been found in the Fraser River in Canada and the Horikawa River in Japan.<sup class="reference" id="cite_ref-Baird_p10_63-1">[64]

Population
Worldwide population estimates are uncertain, but recent consensus suggest an absolute minimum of 50,000.<sup class="reference" id="cite_ref-iucn_1-2">[2] <sup class="reference" id="cite_ref-noaa_22-1">[23] Local estimates include roughly 25,000 in the Antarctic, 8,500 in the tropical Pacific, 2,250–2,700 off the cooler northeast Pacific and 500–1,500 off Norway.<sup class="reference" id="cite_ref-65">[66] Japan's Fisheries Agency estimated there were 2,321 killer whales in the seas around Japan.<sup class="reference" id="cite_ref-66">[67] <sup class="reference" id="cite_ref-67">[68]

Feeding
Killer whales hunt varied prey; however, different populations/species tend to specialize and some can have a dramatic impact on certain preyed species.<sup class="reference" id="cite_ref-68">[69] For example, some populations in the Norwegian and Greenland sea specialize in herring and follow that fish's autumnal migration to the Norwegian coast. Other populations prey on seals. Salmon account for 96% of northeast Pacific residents' diet. 65% of them are large, fatty Chinook.<sup class="reference" id="cite_ref-69">[70] Chum salmon are also eaten, but smaller sockeye and pink salmon are not a significant food item.<sup class="reference" id="cite_ref-70">[71] Depletion of specific prey species in an area is therefore cause for concern for local populations, despite the high diversity of prey. On average, a killer whale eats 227 kilograms (500 lb) each day.<sup class="reference" id="cite_ref-71">[72]

Since some killer whales prey on large whales and sharks, they are considered to be apex predators. They are sometimes called the wolves of the sea, because they hunt in groups like wolf packs.<sup class="reference" id="cite_ref-marinebio_72-0">[73]

Fish and other cold-blooded prey
Fish-eating killer whales prey on around 30 species of fish, particularly Chinook, salmon, herring, and tuna. In New Zealand, rays are killer whales' most frequent prey,<sup class="reference" id="cite_ref-73">[74] and they have also been observed hunting sharks (particularly makos, threshers and smooth hammerheads). Squid and sea turtles are also taken.<sup class="reference" id="cite_ref-74">[75]

Killer whales can induce tonic immobility in sharks and rays by holding them upside down, rendering them helpless and incapable of injuring the whale. Some sharks suffocate within about 15 minutes while the whale holds them still, because these sharks need to move to breathe. In one incident filmed near the Farallon Islands, a female killed a 3–4-metre (9.8–13 ft) long great white shark,<sup class="reference" id="cite_ref-75">[76] apparently after swimming with it upside-down in her mouth and inducing tonic immobility in it. She and another pod member ate the shark's liver and allowed the rest of the carcass to sink.<sup class="reference" id="cite_ref-76">[77]

In July 1992, two killer whales attacked, killed and fed on an 8-metre (26 ft) long whale shark, Rhincodon typus, in the waters off Bahia de los Angeles in Baja California.<sup class="reference" id="cite_ref-77">[78]

While salmon are usually hunted by an individual 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. They then slap the ball with their tail flukes, either stunning or killing up to 10–15 at a time. 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.<sup class="reference" id="cite_ref-78">[79]

Mammal prey
Killer whales are very sophisticated and effective predators. Twenty-two cetacean species have been recorded as killer whale prey, from examining either stomach contents, scarring on the prey's body, or feeding activity. Groups even attack larger cetaceans such as minke whales, gray whales, and rarely sperm whales or blue whales.

Hunting large whales usually takes several hours. Killer whales generally choose to attack young or weak animals instead. However, a group of five or more may attack a healthy adult. When hunting a young whale, a group chases it and its mother until they wear out. Eventually they separate the pair and surround the calf, preventing it from surfacing to breathe, drowning it. Pods of female sperm whales sometimes protect themselves by forming a protective circle around their calves with their flukes facing outwards, using them to repel the attackers.<sup class="reference" id="cite_ref-79">[80]

Other marine mammal prey species include most species of seal, sea lion and fur seal. Walruses and sea otters are less frequently taken. Often, to avoid injury, killer whales 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.<sup class="reference" id="cite_ref-Heimlich_and_Boran_2001.2C_p._45_80-0">[81] Sea lions are killed by head-butting or after a stunning blow from a tail fluke. In the Aleutian Islands, a decline in sea otter populations in the 1990s was controversially attributed by some scientists to killer whale predation, although there is no direct evidence of this.<sup class="reference" id="cite_ref-81">[82] The decline of sea otters followed a decline in harbour seal and Steller sea lion populations, the killer whale's preferred prey,<sup class="reference" id="cite_ref-83">[Note 1] <sup class="reference" id="cite_ref-84">[84] which in turn may be substitutes for their original prey, now decimated by industrial whaling.<sup class="reference" id="cite_ref-85">[85] <sup class="reference" id="cite_ref-86">[86] <sup class="reference" id="cite_ref-87">[87]

In steeply banked beaches 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 temporarily to grab prey before wriggling back to the sea. Beaching, usually fatal to cetaceans, is not an instinctive behavior, and can require years of practice for the young.<sup class="reference" id="cite_ref-88">[88]

"Wave-hunting" killer whales spy-hop to locate Weddell seals, Ross seals, crabeater seals and leopard seals resting on ice floes and then swim in groups to create waves that wash over the floe. This washes the seal into the water where another killer whale waits to kill it.<sup class="reference" id="cite_ref-89">[89]

Killer whales have also been observed preying on terrestrial mammals, such as deer and moose swimming between islands off the northwest coast of North America.<sup class="reference" id="cite_ref-Baird_harbor_seals_82-1">[83] Killer whale cannibalism has also been reported based on analysis of stomach contents, but this is likely to be the result of scavenging remains dumped by whalers.<sup class="reference" id="cite_ref-90">[90] One killer whale was also attacked by its companions after being shot.<sup class="reference" id="cite_ref-Jefferson_et_al_1991_26-1">[27] Although resident killer whales have never been observed to eat other marine mammals, they occasionally harass and kill porpoises and seals for no apparent reason.<sup class="reference" id="cite_ref-91">[91]

Birds
Killer whales in many areas prey on several bird species, including penguins, cormorants and gulls.<sup class="reference" id="cite_ref-92">[92] A captive killer whale at Marineland discovered that it could regurgitate fish onto the surface, attracting sea gulls, and then eat the birds. Four other killer whales then learned to copy the behavior.<sup class="reference" id="cite_ref-93">[93]

Behavior
Day-to-day killer whale behavior generally consists of foraging, travelling, resting and socializing. Killer whales are frequently active at the surface, engaging in acrobatic behaviors such as breaching, spyhopping, and tail-slapping. These activities may have a variety of purposes, such as courtship, communication, dislodging parasites, or play. Spyhopping, a behaviour in which a whale holds its head above water, helps the animal view its surroundings.<sup class="reference" id="cite_ref-94">[94]

Resident killer whales swim with porpoises, other dolphins, seals, and sea lions, which are common prey for transient killer whales.

Social structure
Killer whales are notable for their complex societies. Only elephants and higher primates, such as humans, live in comparably complex social structures.<sup class="reference" id="cite_ref-Heimlich_and_Boran_2001.2C_p._35_51-1">[52] Due to orcas' complex social bonds and society, many marine experts have concerns about how humane it is to keep these animals in captive situations.<sup class="reference" id="cite_ref-95">[95] Resident killer whales in the eastern North Pacific have a particularly complex and stable social grouping system. Unlike any other mammal species whose social structure is known, residents live with their mothers for their entire lives. These societies are based on matrilines consisting of the matriarch and her descendants who form part of the line, as do their descendants. The average size of a matriline is 5.5 animals.<sup class="reference" id="cite_ref-NMFSp12_96-0">[96]

Because females can reach age 90, as many as four generations travel together. These matrilineal groups are highly stable. Individuals separate for only a few hours at a time, to mate or forage. With one exception, the killer whale named Luna, no permanent separation of an individual from a resident matriline has been recorded.<sup class="reference" id="cite_ref-NMFSp12_96-1">[96]

Closely related matrilines form loose aggregations called pods, usually consisting of one to four matrilines. Unlike matrilines, pods may separate for weeks or months at a time.<sup class="reference" id="cite_ref-NMFSp12_96-2">[96] DNA testing indicates that resident males nearly always mate with females from other pods.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._39_97-0">[97]

Clans are the next level of resident social structure, and are composed of pods with similar dialects and common but older maternal heritage. Clan ranges overlap, mingling pods from different clans.<sup class="reference" id="cite_ref-NMFSp12_96-3">[96]

The final association layer, perhaps more arbitrarily-defined than the familial groupings, is called the community and is defined as a set of clans that regularly commingle. Clans within a community do not share vocal patterns.<sup class="reference" id="cite_ref-98">[Note 2]

Transient pods are smaller than resident pods, typically consisting of an adult female and one or two of her offspring. Males typically maintain stronger relationships with their mothers than females. These bonds can extend well into adulthood. Unlike residents, extended or permanent separation of transient offspring from natal matrilines is common, with juveniles and adults of both sexes participating. Some males become “rovers” and do not form long-term associations, occasionally joining groups that contain reproductive females.<sup class="reference" id="cite_ref-99">[98] As in resident clans, transient community members share an acoustic repertoire, although regional differences in vocalizations have been noted.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._14_100-0">[99]

Vocalizations
See also: Whale songLike all cetaceans, killer whales depend heavily on underwater sound for orientation, feeding, and communication. Killer whales produce three categories of sounds: clicks, whistles, and pulsed calls. Clicks are believed to be used primarily for navigation and discriminating prey and other objects in the surrounding environment, but are also commonly heard during social interactions.<sup class="reference" id="cite_ref-noaa_22-2">[23]

Northeast Pacific resident groups tend to be much more vocal than transient groups in the same waters.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._20_101-0">[100] Residents feed primarily on salmon, whose hearing is too poor to detect killer whale calls at any relevant distance. Residents make sounds to identify themselves when they approach another marine mammal.

Transient are typically silent probably to avoid alerting their mammalian prey, all of whom have excellent underwater hearing.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._20_101-1">[100] They sometimes use a single click (called a cryptic click) rather than the long train of clicks observed in other populations.

All members of a resident pod use similar calls, known collectively as a dialect. Dialects are composed of specific numbers and types of discrete, repetitive calls. They are complex and stable over time. Call patterns and structure are distinctive within matrilines. Newborns produce calls similar to their mothers, but have a more limited repertoire.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._14_100-1">[99] Individuals likely learn their dialect through contact with their mother and other pod members.<sup class="reference" id="cite_ref-102">[101] For instance, family-specific calls have been observed more frequently in the days following a calf's birth, which may help the calf learn them.<sup class="reference" id="cite_ref-103">[102] Dialects are probably an important means of maintaining group identity and cohesiveness. Similarity in dialects likely reflects the degree of relatedness between pods, with variation building over time.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_pp._15-16_104-0">[103]

Researchers have not determined whether calls have particular meanings or are associated with specific types of activity. Resident dialects contain 7–17 (mean = 11) distinctive call types. Transient dialects are much different, having only 4–6 discrete calls, none of which they share with residents. All members of the North American west coast transient community express the same basic dialect, although minor regional variation in call types is evident. Preliminary research indicates that offshore killer whales have group-specific dialects that are unlike those of residents and transients.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_pp._15-16_104-1">[103]

Intelligence
Main article: Cetacean intelligenceKiller whales have the second-heaviest brains among marine mammals.<sup class="reference" id="cite_ref-spear_105-0">[104] They can be trained in captivity and are often described as intelligent,<sup class="reference" id="cite_ref-cbs2010_106-0">[105] <sup class="reference" id="cite_ref-carwardine67_107-0">[106] although defining and measuring "intelligence" is difficult in a species whose environment and behavioral strategies are very different from those of humans.<sup class="reference" id="cite_ref-carwardine67_107-1">[106]

Killer whales imitate others, and seem to deliberately teach skills to their kin. This is most strikingly seen when killer whales deliberately beach themselves to catch seals. Off Península Valdés, adults sometimes pull seals off the shoreline and then release them again near juvenile whales, allowing the younger whales to practice the difficult capture technique on the now-weakened prey. Off the Crozet Islands, mothers push their calves onto the beach, waiting to pull the youngster back if needed.<sup class="reference" id="cite_ref-Heimlich_and_Boran_2001.2C_p._45_80-1">[81] <sup class="reference" id="cite_ref-baird6162_108-0">[107]

People who have interacted closely with killer whales offer numerous anecdotes demonstrating the whales' curiosity, playfulness, and ability to solve problems. For example, Alaskan killer whales have not only learned how to steal fish from longlines, but have overcome a variety of techniques designed to stop them, such as the use of unbaited lines as decoys.<sup class="reference" id="cite_ref-obee42_109-0">[108] Once, fishermen placed their boats several miles apart, taking turns retrieving small amounts of their catch, in the hope that the whales would not have enough time to move between boats to steal fish as it was being retrieved. A researcher described what happened next: "It worked really well for a while. Then the whales split into two groups. It didn't even take them an hour to figure it out. They were so thrilled when they figured out what was going on, that we were playing games. They were breaching by the boats."—Craig Matkin<sup class="reference" id="cite_ref-obee42_109-1">[108] In other anecdotes, researchers describe incidents in which wild killer whales playfully tease humans by repeatedly moving objects that the humans are trying to reach,<sup class="reference" id="cite_ref-BF_110-0">[109] or suddenly start to toss around a chunk of ice after a human throws a snowball.<sup class="reference" id="cite_ref-111">[110]

The killer whale's use of dialects and the passing of other learned behaviours from generation to generation have been described as a form of culture.<sup class="reference" id="cite_ref-112">[111] The complex and stable vocal and behavioural cultures of sympatric groups of killer whales (Orcinus orca) appear to have no parallel outside humans and represent an independent evolution of cultural faculties.<sup class="reference" id="cite_ref-rendell_5-1">[6] ==Conservation== In 2008, the IUCN changed its assessment of the killer whale's conservation status from conservation dependent to data deficient, recognizing that one or more killer whale types may actually be separate, endangered species.<sup class="reference" id="cite_ref-iucn_1-3">[2] Depletion of prey species, pollution, large-scale oil spills, and habitat disturbance caused by noise and conflicts with boats are currently the most significant worldwide threats.<sup class="reference" id="cite_ref-iucn_1-4">[2]

Like other animals at the highest trophic levels, the killer whale is particularly at risk of poisoning from accumulation of toxins, including polychlorinated biphenyls (PCBs).<sup class="reference" id="cite_ref-ford99_113-0">[112] European Harbour seals have problems in reproductive and immune functions associated with high levels of PCBs and related contaminants, and a survey off the Washington coast found that PCB levels in killer whales were higher than levels that had caused health problems in harbour seals.<sup class="reference" id="cite_ref-ford99_113-1">[112] Blubber samples in the Norwegian Arctic show higher levels of PCBs, pesticides and brominated flame-retardants than in polar bears. When food is scarce, killer whales metabolize blubber for energy, which increases pollutant concentrations.

In the Pacific Northwest, wild salmon stocks, a main resident food source, have declined dramatically in recent years.<sup class="reference" id="cite_ref-iucn_1-5">[2] On the west coast of Alaska and the Aleutian Islands, seal and sea lion populations have also substantially declined.<sup class="reference" id="cite_ref-114">[113]

In 2005, the United States government listed the southern resident community as an endangered population under the Endangered Species Act.<sup class="reference" id="cite_ref-noaa_22-3">[23] The southern resident community comprises three pods which live mostly in the Georgia and Haro Straits and Puget Sound in British Columbia and Washington. They do not breed outside of their community, which was once estimated at around 200 animals and later shrank to around 90.<sup class="reference" id="cite_ref-Lyke_115-0">[114] In October 2008, the annual survey revealed that seven were missing and presumed dead, reducing the count to 83.<sup class="reference" id="cite_ref-researchers_116-0">[115] This is potentially the largest decline in the population in the past ten years. These deaths can be attributed to declines in chinook salmon.<sup class="reference" id="cite_ref-researchers_116-1">[115]

Noise from shipping, drilling, and other human activities is a significant concern in some key killer whale habitats, including Johnstone Strait and Haro Strait.<sup class="reference" id="cite_ref-117">[116] In the mid-1990s, loud underwater noises from salmon farms were used to deter seals. Killer whales also avoided the surrounding waters.<sup class="reference" id="cite_ref-118">[117] High-intensity sonar used by the Navy disturbs killer whales along with other marine mammals.<sup class="reference" id="cite_ref-119">[118] Killer whales are popular with whale watchers, which may stress the whales and alter their behavior, particularly if boats approach too closely or block their line of travel.<sup class="reference" id="cite_ref-120">[119]

The Exxon Valdez oil spill adversely affected killer whales in Prince William Sound and Alaska's Kenai Fjords region. Eleven members (about half) of one resident pod disappeared in the following year. The spill damaged salmon and other prey populations, which in turn damaged local killer whales. By 2009, scientists estimated the AT1 transient population (considered part of a larger population of 346 transients), numbered only 7 individuals and had not reproduced since the spill. This population is expected to die out.<sup class="reference" id="cite_ref-121">[120] <sup class="reference" id="cite_ref-122">[121]

Indigenous cultures
The indigenous peoples of the Pacific Northwest Coast feature killer whales throughout their history, art, spirituality and religion. The Haida regarded killer whales as the most powerful animals in the ocean, and their mythology tells of killer whales living in houses and towns under the sea. According to these myths, killer whales took on human form when submerged, and humans who drowned went to live with them.<sup class="reference" id="cite_ref-francis115_123-0">[122] For the Kwakwaka'wakw, the killer whale was regarded as the ruler of the undersea world, with sea lions for slaves and dolphins for warriors.<sup class="reference" id="cite_ref-francis115_123-1">[122] In Kwakwaka'wakw and Nuu-chah-nulth mythology, killer whales may embody the souls of deceased chiefs.<sup class="reference" id="cite_ref-francis115_123-2">[122] The Tlingit of southeastern Alaska regarded the killer whale as custodian of the sea and a benefactor of humans.<sup class="reference" id="cite_ref-124">[123]

The Maritime Archaic people of Newfoundland also had great respect for killer whales, as evidenced by stone carvings found in a 4,000 year old burial site at the Port au Choix National Historic Site.<sup class="reference" id="cite_ref-125">[124] <sup class="reference" id="cite_ref-126">[125]

In the tales and beliefs of the Siberian Yupik people, killer whales are said to appear as wolves in winter, and wolves as killer whales in summer.<sup class="reference" id="cite_ref-rubow_127-0">[126] <sup class="reference" id="cite_ref-menow_128-0">[127] <sup class="reference" id="cite_ref-ssipr_129-0">[128] <sup class="reference" id="cite_ref-submit_130-0">[129] Killer whales are believed to assist their hunters in driving walrus.<sup class="reference" id="cite_ref-radio_131-0">[130] Reverence is expressed in several forms: the boat represents the animal, and a wooden carving hung from the hunter's belt.<sup class="reference" id="cite_ref-ssipr_129-1">[128] Small sacrifices such as tobacco are strewn into the sea for them.<sup class="reference" id="cite_ref-radio_131-1">[130] Killer whales were believed to have helped the hunters even when in wolf guise, by forcing reindeer to allow themselves to be killed.<sup class="reference" id="cite_ref-submit_130-1">[129]

"Killer" stereotype
In Western cultures, killer whales were historically feared as dangerous, savage predators.<sup class="reference" id="cite_ref-Obee1_132-0">[131] The first written description of a killer whale was given by Pliny the Elder in circa AD 70, who wrote, "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."<sup class="reference" id="cite_ref-133">[132]

There have been very few confirmed attacks on humans by wild killer whales, none of which has been fatal.<sup class="reference" id="cite_ref-134">[133] In one instance, killer whales tried to tip ice floes on which a dog team and photographer of the Terra Nova Expedition was standing.<sup class="reference" id="cite_ref-135">[134] There is speculation that the sled dogs' barking may have sounded enough like seal calls to trigger the killer whale's hunting curiosity. In the 1970s, a surfer in California was bitten, and in 2005 a boy in Alaska who was splashing in a region frequented by harbor seals was bumped by a killer whale that apparently misidentified him as prey.<sup class="reference" id="cite_ref-ketchikan_136-0">[135] Unlike wild killer whales, captive killer whales are reported to have made nearly two dozen attacks on humans since the 1970s, some of which have been fatal.<sup class="reference" id="cite_ref-abc2006_137-0">[136] <sup class="reference" id="cite_ref-138">[137]

Competition with fishermen also led to killer whales being regarded as pests. In the waters of the Pacific Northwest and Iceland, the shooting of killer whales was accepted and even encouraged by governments.<sup class="reference" id="cite_ref-Obee1_132-1">[131] As an indication of the intensity of shooting that occurred until fairly recently, about 25% of the killer whales captured in Puget Sound for aquaria through 1970 bore bullet scars.<sup class="reference" id="cite_ref-139">[138] The U.S. Navy claimed to have deliberately killed hundreds of killer whales in Icelandic waters in 1956.<sup class="reference" id="cite_ref-140">[139] <sup class="reference" id="cite_ref-141">[140]

Modern Western attitudes
See also: Killer Whales in popular cultureWestern attitudes towards killer whales have changed dramatically in recent decades. In the mid 1960s and early 1970s, killer whales came to much greater public and scientific awareness, starting with the first live-capture and display of a killer whale known as Moby Doll, a resident that had been harpooned off Saturna Island in 1964.<sup class="reference" id="cite_ref-Obee1_132-2">[131] So little was known at the time that it was nearly two months before the whale's keepers discovered what food (fish) it was willing to eat. To the surprise of those who saw him, Moby Doll was a docile, non-aggressive whale that made no attempts to attack humans.<sup class="reference" id="cite_ref-142">[141]

Between 1964 and 1976, 50 killer whales from the Pacific Northwest were captured for display in aquaria, and public interest in the animals grew. Millions of people became interested in killer whales after viewing them in captivity. In the 1970s, research pioneered by Michael Bigg led to the discovery of the species' complex social structure, its use of vocal communication, and its extraordinarily stable mother-offspring bonds. Through photo-identification techniques, individuals were named and tracked over decades.<sup class="reference" id="cite_ref-143">[142]

Bigg's techniques also revealed that the Pacific Northwest population was small—in the low hundreds rather than the thousands that had been previously assumed.<sup class="reference" id="cite_ref-Obee1_132-3">[131] The Southern Resident community alone had lost 48 of its members to captivity; by 1976, only 80 remained.<sup class="reference" id="cite_ref-144">[143] In the Pacific Northwest, the species that had unthinkingly been targeted became a cultural icon within a few decades.<sup class="reference" id="cite_ref-Lyke_115-1">[114]

The public's growing appreciation also led to growing opposition to whale–keeping in aquaria. Only one whale has been taken in North American waters since 1976. In recent years, the extent of the public's interest in killer whales has manifested itself in several high-profile efforts surrounding individuals. Following the success of the 1993 film Free Willy, the movie's captive star Keiko was returned to the coast of his native Iceland. In 2002, the orphan Springer was discovered in Puget Sound, Washington. She became the first whale to be successfully reintegrated into a wild pod after human intervention, crystallizing decades of research into the vocal behavior and social structure of the region's killer whales.<sup class="reference" id="cite_ref-CBC_145-0">[144] The saving of Springer raised hopes that another young killer whale named Luna who had become separated from his pod could be returned to it. However, his case was marked by controversy about whether and how to intervene, and in 2006 Luna was killed by a boat propeller.<sup class="reference" id="cite_ref-146">[145]

Whaling
The first records of commercial hunting of killer whales date to the 18th century in Japan. During the 19th and early 20th centuries, the global whaling industry caught immense numbers of baleen and sperm whales, but largely ignored killer whales because of their limited amounts of recoverable oil, their smaller populations, and the difficulty of taking them.<sup class="reference" id="cite_ref-NMFS_.282005.29.2C_p._39_97-1">[97] Once the stocks of larger species were depleted, killer whales were targeted by commercial whalers in the mid-20th century. Between 1954 and 1997, Japan took 1,178 killer whales and Norway took 987.<sup class="reference" id="cite_ref-Obee.2C_p._34_147-0">[146] Over 3,000 killer whales were taken by Soviet whalers,<sup class="reference" id="cite_ref-148">[147] including an Antarctic catch of 916 in 1979-80 alone, prompting the International Whaling Commission to recommend a ban on commercial hunting of the species pending further research.<sup class="reference" id="cite_ref-Obee.2C_p._34_147-1">[146] Today, no country carries out a substantial hunt, although Indonesia and Greenland permit small subsistence hunts.

Killer whales have helped humans hunting other whales.<sup class="reference" id="cite_ref-scavenging_149-0">[148] One well-known example was in Eden, Australia, including the male known as Old Tom. Whalers more often considered them a nuisance, however, as they would gather to scavenge meat from the whalers' catch.<sup class="reference" id="cite_ref-scavenging_149-1">[148] Some populations, such as in Alaska's Prince William Sound, may have been reduced significantly by whalers shooting them in retaliation.<sup class="reference" id="cite_ref-baird_15-1">[16]

Captivity
Main article: Captive orcasThe killer whale's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquariums and aquatic theme parks.<sup class="reference" id="cite_ref-nmfs43_150-0">[149] From 1976–1997, 55 whales were taken from the wild in Iceland, 19 from Japan, and three from Argentina. These figures exclude animals that died during capture.<sup class="reference" id="cite_ref-nmfs43_150-1">[149] Live captures fell dramatically in the 1990s, and by 1999, about 40% of the 48 animals on display in the world were captive–born.<sup class="reference" id="cite_ref-nmfs43_150-2">[149]

Organizations such as the World Society for the Protection of Animals and the Whale and Dolphin Conservation Society campaign against the practice of keeping them in captivity. In captivity they often develop pathologies, such as the dorsal fin collapse seen in 60–90% of captive males. Captives have vastly reduced life expectancies, on average only living into their 20s.<sup class="reference" id="cite_ref-151">[Note 3] In the wild, females who survive infancy live 50 years on average, and up to 70–80 years in rare cases. Wild males who survive infancy live 30 years on average, and up to 50–60 years.<sup class="reference" id="cite_ref-152">[150] Captivity usually bears little resemblance to wild habitat, and captive whales' social groups are foreign to those found in the wild. Critics claim that captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild killer whale behavior.<sup class="reference" id="cite_ref-153">[151] Wild killer whales travel up to 160 kilometres (100 mi) each day, and critics say that the animals are too big and intelligent to be suitable for captivity.<sup class="reference" id="cite_ref-cbs2010_106-1">[105]

Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress.<sup class="reference" id="cite_ref-abc2006_137-1">[136] <sup class="reference" id="cite_ref-hoyt1992_154-0">[152] <sup class="reference" id="cite_ref-nytimes2010_155-0">[153] Tilikum, a captive killer whale born in the wild, has been involved in three fatalities including one in which he grabbed a trainer and pulled her underwater, eventually drowning her.<sup class="reference" id="cite_ref-CSMon_156-0">[154] Experts are divided as to whether the injuries and deaths caused by captive killer whales have been accidents or deliberate attempts to cause harm.<sup class="reference" id="cite_ref-CSMon_156-1">[154]