Killer whale
The killer whale (Orcinus orca), commonly referred to as the orca – and, less commonly, blackfish – is the largest species of the oceanic dolphin family. They are found in all of the world's oceans, from the frigid Arctic and Antarctic regions to tropical seas. Killer whales as a species have a diverse diet, although populations often specialize in particular types of prey. Some feed exclusively on fish, while other populations hunt marine mammals such as sea lions, seals, walruses and even large whales. Killer whales are regarded as apex predators as they have no natural predators.
Researchers have identified five distinct killer whale types distinguished by geographical range, preferred prey 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.[3] The sophisticated hunting techniques and vocal behaviours of killer whales, which are often specific to a particular group and passed from one generation to the next, have been described as manifestations of culture.
The IUCN currently assesses the conservation status of the killer whale as data deficient because of the likelihood that one or more killer whale types could actually be a separate species in need of protection. Some local populations are considered threatened or endangered due to depletion of prey species, habitat loss, pollution by PCBs, historic 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,[4] although there have been cases of captive killer whales killing or injuring their handlers at marine theme parks. The killer whale features strongly in the mythologies of indigenous cultures. In Western cultures, it has had a reputation for being a fearsome predator, but in recent decades better understanding has led to widespread appreciation of the species.
Contents |
Taxonomy and evolution
Orcinus orca is the only recognized species in the genus Orcinus, one of many species originally described by Linnaeus in 1758 in Systema Naturae.[5] 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.[6]
The killer whale is one of 35 species in the 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 pilot whales and pygmy killer whales, its closest relative is the Irrawaddy dolphin.[8]
Common names
English-speaking scientists most often use the term killer whale,[9] 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 or belonging to the kingdom of the dead",[9] 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.
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",[10] and because the species is more closely related to dolphins than to other whales.
They are sometimes referred to as blackfish, a name used for other 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.[11]
Types
There are three to five types of killer whales that may be distinct enough to be considered different races,[12] subspecies, or possibly even species.[13] 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:
- 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.[14] Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner.[15] They are known to 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.[16]
- Transient: The diet of these whales consists almost exclusively of marine mammals; they do not eat fish.[15] 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.[15] 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.[15] Transients roam widely along the coast—some individuals have been sighted in both southern Alaska and California.[17]
- Offshore: A third population of killer whales in the northeast Pacific was discovered in 1988 when humpback whale researcher Jim Darling informed killer whale researchers Michael Bigg and Graeme Ellis that he saw some in open water. As suggested by their name, they travel far from shore and are believed to feed primarily on schooling fish.[18] 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 dismissed. 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 animals with occasional sightings of larger groups up to 200 whales.[19] Currently, little is known about their habits, but they can be distinguished genetically from residents and transients. Offshores appear to be smaller than residents or transients, and females are characterized by dorsal fin tips that are continuously rounded.[15]
Transient and resident killer whales live in the same areas, but avoid each other.[20] 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.[21] Genetic research indicates that the types have not interbred for up to 10,000 years.[22]
Killer whale populations in other parts of the world have not been as well studied, although specialized fish-eating and mammal-eating killer whales have also been distinguished elsewhere.[23] Separate populations of fish-eating and mammal-eating killer whales have been identified around the United Kingdom.[24][25] Fish-eating killer whales in Alaska and Norway have been observed to have resident-like social structures, while mammal-eating killer whales in Argentina and the Crozet Islands have been observed to behave more like transients.[26]
Three killer whale types have recently 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 were skeptical about their status, and it is difficult to link these directly to the types described below.[13]
- 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.[13]
- 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"[27] stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals.[13]
- Type C is the smallest type and lives in larger groups than any other type. 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.[13]
Types B and C live close to the Antarctic ice pack, and diatoms in these waters may be responsible for the yellowish colouring of both types.[13][28] Mitochondrial DNA sequences support the theory that these are separate species that have recently diverged.[29]
Research is ongoing into the genetic relationships between killer whale types, and whether the types that have been identified represent deep evolutionary trends. For example, it was long presumed that mammal-eating killer whales were likely to be closely related to other mammal-eating killer whales from different regions, but genetic testing has found that this is not the case.[30]
Description
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 robust body (more so than other dolphins)[31] 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 unlikely to be confused with any other sea creature.[32] 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).[33] 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).[33] 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).[34] Calves at birth weigh about 180 kilograms (397 lb) and are about 2.4 metres (7.9 ft) long.[35][36] 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).[37]
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.[38] Males and females also have different patterns of black and white skin in the genital area.[39]
Individual killer whales can often be identified by a good view of 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.[40]
White killer whales occur sporadically among normal whales, but are rare. They have been spotted in the northern Bering Sea and around St. Lawrence Island, and the Russian coast. In February 2008, a white killer whale was photographed 2 miles (3 km) off Kanaga Volcano.[41][42]
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.[43]
Life cycle
Female killer whales become mature at around age 15. Then they have periods of polyestrous cycling with non-cycling periods of between 3 and 16 months. The gestation period 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 months of life, when 37–50% of all calves die.[44] Calves lactation for up to two years but start to take solid food at about 12 months. According to observations in several regions, all male and female killer whale pod members participate in the care of the young.[45]
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.[46] Males become 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.[46] 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,[47] but this method is now believed to be inaccurate for older animals.[48] 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.[49] Captive killer whale lifespans are typically 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 killer whales depend on the will of the animal.[50][51]
Range and habitat
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, they generally prefer coastal areas to pelagic environments.[52] 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. The killer whale is particularly highly concentrated in the northeast Pacific Ocean, from Alaska to Washington, and the coasts of Antarctica, Iceland and northern Norway. They are also numerous, to a lesser extent, around central California, Argentina, New Zealand and the Crozet Islands.
The largest population lives in Antarctic waters, where they range up to the ice pack and are believed to venture under the pack, surviving by breathing in air pockets as do beluga whales in the Arctic. Killer whales visit Arctic waters in summer, but are rarely seen in winter and do not approach the ice pack. With the rapid Arctic sea ice decline in the Hudson Strait, their range now extends into Canada's far northern waters. In the 1990s, killer whales were sighted in western Hudson Bay only 6 times; there were over 30 sightings from 2001–2006.[53]
Worldwide population estimates are uncertain, but one recent study estimated more than 50,000.[19] 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.[54] Japan's Fisheries Agency estimated there were 2,321 killer whales in the seas around Japan.[55][56]
Killer whales' migration patterns 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.[57]
Occasionally, killer whales have been known to swim into freshwater rivers. They have been documented 100 miles (161 km) up the Columbia River in the United States.[58][59] They have also been found in the Fraser River in Canada and the Horikawa River in Japan.[58]
Feeding
Killer whales prey on many different species, however, populations tend to show a high degree of specialization. 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. Field observations of northeast Pacific resident killer whales show that salmon accounted for 96% of their diet, with 65% of salmon prey being the large, fatty Chinook.[60] Chum salmon are also eaten, but smaller sockeye and pink salmon are not a significant food item.[61] 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.[62]
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.[63]
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,[64] and they have also been observed hunting sharks (particularly makos, threshers and smooth hammerheads). Squid and sea turtles are also taken.[65]
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 will suffocate within about 15 minutes when held still because these sharks need to be moving 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,[66] 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 nutritious liver and allowed the rest of the carcass to sink.[67]
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.[68]
While salmon are usually hunted by a single or 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 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.[69]
Mammal prey
Killer whales are strikingly 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, and killer whales generally choose to attack young or weak whales. However, a group of five or more may attack healthy adults. When hunting a young whale, a group chases it and its mother until they wear out. Eventually they separate the pair and surround the young whale, preventing it from surfacing to breathe. Whales are typically drowned in this manner. Pods of female sperm whales can sometimes protect themselves by forming a protective circle around their calves with their flukes facing outwards, using their powerful flukes to repel the attackers.[70]
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.[71] Sea lions are killed by head-butting or after a stunning blow from a tail fluke. They occasionally throw seals into the air in order to stun and kill them. 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 that killer whales were responsible.[72] The decline of sea otters followed a decline in harbour seal and Steller sea lion populations, the killer whale's preferred prey,[73][74] which in turn may be substitutes for their original prey, now decimated by industrial whaling.[75][76][77]
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 themselves temporarily to grab their prey before wriggling back to the sea. Beaching, usually fatal to cetaceans, is not an instinctive behaviour, and can require years of practice for young killer whales.[78]
"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.[79]
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.[80] Killer whale cannibalism has also been reported based on analysis of stomach contents, but this is likely to have been the result of scavenging the remains of whales dumped by whaling ships.[81] One killer whale was also attacked by its companions after being shot.[23] 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.[82]
Birds
Killer whales in many areas have been observed to prey on several bird species, including penguins, cormorants and sea gulls.[83] 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 behaviour.[84]
Behavior
In the latest article
-
Unreviewed
Orcinus orca (Linnaeus, 1758)
This article is unpublished.
Source information
Some rights reserved
View source
Supplier:
Wikipedia
"Killer whale." Wikipedia, The Free Encyclopedia. 23 Mar 2010, 03:36 UTC. 24 Mar 2010 <http://en.wikipedia.org/w/index.php?title=Killer_whale&oldid=351312119>.
Revisions
- 2013-05-17 01:27:24 UTC
- 2013-05-03 01:49:26 UTC
- 2013-04-12 15:03:10 UTC
- 2013-03-29 01:22:05 UTC
- 2013-03-24 07:16:54 UTC
- 2013-03-16 02:51:07 UTC
- 2013-03-10 06:54:05 UTC
- 2013-02-23 06:58:15 UTC
- 2013-02-08 15:01:54 UTC
- 2013-01-12 04:36:20 UTC
- 2013-01-06 08:44:43 UTC
- 2012-12-29 02:47:55 UTC
- 2012-12-14 04:15:35 UTC
- 2012-12-07 05:56:36 UTC
- 2012-11-21 00:42:10 UTC
- 2012-11-14 05:00:41 UTC
- 2012-11-07 12:36:54 UTC
- 2012-10-17 03:17:27 UTC
- 2012-09-26 02:52:30 UTC
- 2012-09-12 02:30:37 UTC
- 2012-08-29 02:44:25 UTC
- 2012-08-22 02:41:53 UTC
- 2012-08-15 02:37:32 UTC
- 2012-08-08 03:11:11 UTC
- 2012-08-01 02:55:04 UTC
- 2012-07-27 04:02:11 UTC
- 2012-07-18 08:36:57 UTC
- 2012-07-11 05:41:32 UTC
- 2012-06-21 05:53:25 UTC
- 2012-06-14 05:23:03 UTC
- 2012-06-06 03:56:58 UTC
- 2012-05-30 04:27:43 UTC
- 2012-05-16 04:10:48 UTC
- 2012-05-09 05:59:04 UTC
- 2012-05-02 03:08:45 UTC
- 2012-04-25 02:50:16 UTC
- 2012-04-18 02:54:55 UTC
- 2012-04-11 03:03:59 UTC
- 2012-04-04 02:53:36 UTC
- 2012-03-28 04:09:22 UTC
- 2012-03-21 03:10:29 UTC
- 2012-02-25 04:59:12 UTC
- 2012-01-25 10:24:07 UTC
- 2012-01-02 06:42:25 UTC
- 2011-12-15 03:33:08 UTC
- 2011-12-07 05:34:12 UTC
- 2011-11-15 04:26:31 UTC
- 2011-11-01 01:00:26 UTC
- 2011-10-25 02:35:00 UTC
- 2011-10-20 03:13:11 UTC
- 2011-10-18 02:27:14 UTC
- 2011-10-17 05:32:24 UTC
- 2011-08-23 13:37:14 UTC
- 2011-08-16 08:09:26 UTC
- 2011-06-08 04:38:28 UTC
- 2011-05-24 12:33:19 UTC
- 2011-05-08 05:03:35 UTC
- 2011-04-24 03:49:19 UTC
- 2011-04-10 03:00:20 UTC
- 2011-02-09 08:13:38 UTC
- 2011-01-27 03:51:52 UTC
- 2011-01-12 01:17:51 UTC
- 2010-05-11 03:12:20 UTC
- 2010-03-26 03:34:31 UTC
- 2010-02-26 10:46:13 UTC
- 2009-12-23 17:00:39 UTC
- 2009-10-15 10:05:46 UTC
