Post by Vodmeister on Mar 1, 2014 2:04:21 GMT 5
Orcinus orca
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Orcinus
Species: Orcinus orca
The killer whale (Orcinus orca), also referred to as the orca whale or 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 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.
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 two 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 "southern resident" population of killer whales that inhabits British Columbia and Washington state waters 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.[8] Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers.
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.[9] 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.[10]
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, a study of cytochrome b gene sequences by Richard LeDuc indicated that its closest extant relatives are the snubfin dolphins of the genus Orcaella.[11]
Common names
English-speaking scientists most often use the term "killer whale", although the term "orca" is increasingly used. Killer whale advocates point out it has a long heritage. Indeed, the genus name Orcinus means "of the kingdom of the dead",[12] or "belonging to Orcus".[13] 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",[14] and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.[15]
According to some authors, the name killer whale would be a mistranslation of the 18th century Spanish name asesina ballenas which means literally whale killer.[16] Basque whalers would have given it such name after observing pods of orcas hunting their own prey.
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.[17]
Types
The three to five types of killer whales may be distinct enough to be considered different races,[18] subspecies, or possibly even species.[19] 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] Although large variation in the ecological distinctiveness of different killer whale groups complicate simple differentiation into types,[20] research off the west coast of Canada and the United States in the 1970s and 1980s 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' diets consist primarily of fish[21] and sometimes squid, and they live in complex and cohesive family groups called pods.[22] Female residents characteristically have rounded dorsal fin tips that terminate in a sharp corner.[23] 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.[24]
Transient: The diets of these whales consist almost exclusively of marine mammals.[21][23] Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents.[25] Transients vocalize in less variable and less complex dialects.[26] Female transients are characterized by more triangular and pointed dorsal fins than those of residents.[23] 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.[23] Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California.[27] Transients are also referred to as Bigg's killer whale in honor of Michael Bigg. The term has become increasingly common and may eventually replace the transient label.[28]
Offshore: A third population of killer whales in the northeast Pacific was discovered in 1988, when a humpback whale researcher observed them in open water. As their name suggests, they travel far from shore and feed primarily on schooling fish.[29] However, because they have large, scarred and nicked dorsal fins resembling those of mammal-hunting transients, it may be that they also eat mammals and sharks.[30][31] 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.[32] 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.
Morphology
Internal anatomy of an orca
A typical killer whale distinctively bears 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. It has a heavy and robust body[52] with a large dorsal fin up to 2 m (6.6 ft) tall. Behind the fin, it has 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.[53] When seen from a distance, juveniles can be confused with other cetacean species, such as the false killer whale or Risso's dolphin.[54] The killer whale's teeth are very strong and covered in enamel. Its jaws are a powerful gripping apparatus, as the upper teeth fall into the gaps between the lower teeth when the mouth is closed. The front teeth are inclined slightly forward and outward, thus allowing the killer whale to withstand powerful jerking movements from its prey while the middle and back teeth hold it firmly in place.[55]
Killer whales are the largest extant members of the dolphin family. Males typically range from 6 to 8 metres (20 to 26 ft) long and weigh in excess of 6 tonnes (5.9 long tons; 6.6 short tons). Females are smaller, generally ranging from 5 to 7 m (16 to 23 ft) and weighing about 3 to 4 tonnes (3.0 to 3.9 long tons; 3.3 to 4.4 short tons).[56] The largest male killer whale on record was 9.8 m (32 ft), weighing over 10 tonnes (9.8 long tons; 11 short tons), while the largest female was 8.5 m (28 ft), weighing 7.5 tonnes (7.4 long tons; 8.3 short tons).[57] Calves at birth weigh about 180 kg (400 lb) and are about 2.4 m (7.9 ft) long.[58][59] 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).[60] The skeleton of the killer whale is of the typical delphinid structure, but is more robust.[61] Its integument, unlike that of most other dolphin species, is characterised by a well-developed dermal layer with a dense network of fascicles of collagen fibers.[62]
Killer whale pectoral fins are large and rounded, resembling paddles. Males have significantly larger pectoral fins than females. At about 1.8 m (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.[63] Males and females also have different patterns of black and white skin in their genital areas.[64] Sexual dimorphism is also apparent in the skull; adult males have longer lower jaws than females, and have larger occipital crests.[62]
An individual killer whale can often be identified from its 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. Photographic 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.[65]
White killer whales occur sporadically but rarely among normal killer whales; they have been spotted in the northern Bering Sea and around St. Lawrence Island, and near the Russian coast.[32][66] In February 2008, a white killer whale was photographed 2 mi (3.2 km) off Kanaga Volcano in the Aleutian Islands.[32][66]
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 environments by emitting clicks and listening for echoes.[67]
The mean body temperature of the orca is 36.0 to 38°C.[68][69] Like most marine mammals, orcas have a layer of insulating blubber (7.6 to 10 cm thick[68]) beneath its skin.
The heart beats at a rate of about 60 beats/min when the orca is at the surface, dropping to 30 beats/min when submerged.[70]
Life cycle
Back and dorsal fin of killer whale projecting above the sea surface, including the grey saddle patch and part of the white eye patch: The dorsal fin rises steeply to a rounded point.
An adult male killer whale with its characteristic tall dorsal fin swims in the waters near Tysfjord, Norway
Female killer whales mature at around age 15. They then have periods of polyestrous cycling with noncycling periods of between three and 16 months. Gestation varies from 15 to 18 months. Mothers calve, with usually a single offspring, about once every five years. In resident pods, births occur at any time of year, although winter is the most common. Mortality is extremely high during the first six to seven months of life, when 37–50% of all calves die.[71] 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.[72] Killer and pilot whales are two of several species (as is now believed to be widespread among many other mammalian species, including humans) where the females are known to go through menopause and live for decades after they have finished breeding.[73][74] Killer whales are unique among cetaceans, as their heads become shorter as they age.[62]
Females breed until age 40, meaning on average they raise five offspring. The lifespans of wild females average 50 years, with a maximum of 80–90 years.[75] 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.[75] 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,[76] but this method of age determination is now believed to be inaccurate for older animals.[77] One male known to researchers in the Pacific Northwest (identified as J1) was estimated to have been 59 years old when he died in 2010.[78] Captive killer whale lifespans are typically significantly shorter, usually less than 25 years; however, numerous individuals are alive in their 30s, and a few have reached their 40s.
Range and habitat
A killer whale bursts forward out of the water. Its head is just starting to point downward, and is about a body width above the surface.
A killer whale leaps out of the water when swimming—a behaviour known as porpoising
Killer whales are found in all oceans and most seas. Due to their enormous range, numbers, and density, distributional estimates are difficult to compare,[81] but they clearly prefer higher latitudes and coastal areas over pelagic environments.[82]
Systematic surveys indicate the highest densities of killer whales (>0.40 individuals per 100 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.[81] 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.[81] Information for offshore regions and tropical waters is more scarce, but widespread, if not frequent, sightings indicate the killer whale can survive in most water temperatures. They have been sighted, for example, in the Mediterranean, the Arabian Sea, the Gulf of Mexico and the Indian Ocean around the Seychelles.[81]
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.[83]
Migration patterns are poorly understood. Each summer, the same individuals appear off the coasts of British Columbia and Washington. 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.[84] Resident killer whales sometimes travel as much as 160 km (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 mi (160 km) up the Columbia River in the United States.[85][86] They have also been found in the Fraser River in Canada and the Horikawa River in Japan.[85]
Population
Worldwide population estimates are uncertain, but recent consensus suggests an absolute minimum of 50,000.[2][32] 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.[87] Japan's Fisheries Agency estimated 2,321 killer whales were in the seas around Japan.[88][89]
Feeding
A skeleton is suspended on metal framework, which incorporates an outline of the soft tissue along a median cross-section of the animal. The jaws host many sharp teeth, and pectoral fin bones are attached to the lower ribs. The backbone stretches away out of frame; no hind limb bones can be seen. The outline includes an upright dorsal fin and rounded forehead.
A killer whale skeleton
Killer whales hunt varied prey; however, different populations or species tend to specialize and some can have a dramatic impact on certain prey species.[90] 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. About 65% of them are large, fatty Chinook.[91] Chum salmon are also eaten, but smaller sockeye and pink salmon are not a significant food item.[92] 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.[93]
Killer whales are apex predators, meaning that they themselves have no natural predators. They are sometimes called the wolves of the sea, because they hunt in groups like wolf packs.[94]
Each population seems to prefer one kind of prey. Those that feed on whales may not even recognize fish as food. This specialization in diet and hunting, combined with small differences in markings, suggest that they might be different species, rather than populations. Advanced methods that sequenced the entire mitochondrial genome revealed systematic differences in DNA between different populations.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus: Orcinus
Species: Orcinus orca
The killer whale (Orcinus orca), also referred to as the orca whale or 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 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.
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 two 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 "southern resident" population of killer whales that inhabits British Columbia and Washington state waters 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.[8] Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers.
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.[9] 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.[10]
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, a study of cytochrome b gene sequences by Richard LeDuc indicated that its closest extant relatives are the snubfin dolphins of the genus Orcaella.[11]
Common names
English-speaking scientists most often use the term "killer whale", although the term "orca" is increasingly used. Killer whale advocates point out it has a long heritage. Indeed, the genus name Orcinus means "of the kingdom of the dead",[12] or "belonging to Orcus".[13] 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",[14] and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.[15]
According to some authors, the name killer whale would be a mistranslation of the 18th century Spanish name asesina ballenas which means literally whale killer.[16] Basque whalers would have given it such name after observing pods of orcas hunting their own prey.
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.[17]
Types
The three to five types of killer whales may be distinct enough to be considered different races,[18] subspecies, or possibly even species.[19] 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] Although large variation in the ecological distinctiveness of different killer whale groups complicate simple differentiation into types,[20] research off the west coast of Canada and the United States in the 1970s and 1980s 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' diets consist primarily of fish[21] and sometimes squid, and they live in complex and cohesive family groups called pods.[22] Female residents characteristically have rounded dorsal fin tips that terminate in a sharp corner.[23] 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.[24]
Transient: The diets of these whales consist almost exclusively of marine mammals.[21][23] Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents.[25] Transients vocalize in less variable and less complex dialects.[26] Female transients are characterized by more triangular and pointed dorsal fins than those of residents.[23] 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.[23] Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California.[27] Transients are also referred to as Bigg's killer whale in honor of Michael Bigg. The term has become increasingly common and may eventually replace the transient label.[28]
Offshore: A third population of killer whales in the northeast Pacific was discovered in 1988, when a humpback whale researcher observed them in open water. As their name suggests, they travel far from shore and feed primarily on schooling fish.[29] However, because they have large, scarred and nicked dorsal fins resembling those of mammal-hunting transients, it may be that they also eat mammals and sharks.[30][31] 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.[32] 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.
Morphology
Internal anatomy of an orca
A typical killer whale distinctively bears 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. It has a heavy and robust body[52] with a large dorsal fin up to 2 m (6.6 ft) tall. Behind the fin, it has 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.[53] When seen from a distance, juveniles can be confused with other cetacean species, such as the false killer whale or Risso's dolphin.[54] The killer whale's teeth are very strong and covered in enamel. Its jaws are a powerful gripping apparatus, as the upper teeth fall into the gaps between the lower teeth when the mouth is closed. The front teeth are inclined slightly forward and outward, thus allowing the killer whale to withstand powerful jerking movements from its prey while the middle and back teeth hold it firmly in place.[55]
Killer whales are the largest extant members of the dolphin family. Males typically range from 6 to 8 metres (20 to 26 ft) long and weigh in excess of 6 tonnes (5.9 long tons; 6.6 short tons). Females are smaller, generally ranging from 5 to 7 m (16 to 23 ft) and weighing about 3 to 4 tonnes (3.0 to 3.9 long tons; 3.3 to 4.4 short tons).[56] The largest male killer whale on record was 9.8 m (32 ft), weighing over 10 tonnes (9.8 long tons; 11 short tons), while the largest female was 8.5 m (28 ft), weighing 7.5 tonnes (7.4 long tons; 8.3 short tons).[57] Calves at birth weigh about 180 kg (400 lb) and are about 2.4 m (7.9 ft) long.[58][59] 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).[60] The skeleton of the killer whale is of the typical delphinid structure, but is more robust.[61] Its integument, unlike that of most other dolphin species, is characterised by a well-developed dermal layer with a dense network of fascicles of collagen fibers.[62]
Killer whale pectoral fins are large and rounded, resembling paddles. Males have significantly larger pectoral fins than females. At about 1.8 m (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.[63] Males and females also have different patterns of black and white skin in their genital areas.[64] Sexual dimorphism is also apparent in the skull; adult males have longer lower jaws than females, and have larger occipital crests.[62]
An individual killer whale can often be identified from its 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. Photographic 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.[65]
White killer whales occur sporadically but rarely among normal killer whales; they have been spotted in the northern Bering Sea and around St. Lawrence Island, and near the Russian coast.[32][66] In February 2008, a white killer whale was photographed 2 mi (3.2 km) off Kanaga Volcano in the Aleutian Islands.[32][66]
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 environments by emitting clicks and listening for echoes.[67]
The mean body temperature of the orca is 36.0 to 38°C.[68][69] Like most marine mammals, orcas have a layer of insulating blubber (7.6 to 10 cm thick[68]) beneath its skin.
The heart beats at a rate of about 60 beats/min when the orca is at the surface, dropping to 30 beats/min when submerged.[70]
Life cycle
Back and dorsal fin of killer whale projecting above the sea surface, including the grey saddle patch and part of the white eye patch: The dorsal fin rises steeply to a rounded point.
An adult male killer whale with its characteristic tall dorsal fin swims in the waters near Tysfjord, Norway
Female killer whales mature at around age 15. They then have periods of polyestrous cycling with noncycling periods of between three and 16 months. Gestation varies from 15 to 18 months. Mothers calve, with usually a single offspring, about once every five years. In resident pods, births occur at any time of year, although winter is the most common. Mortality is extremely high during the first six to seven months of life, when 37–50% of all calves die.[71] 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.[72] Killer and pilot whales are two of several species (as is now believed to be widespread among many other mammalian species, including humans) where the females are known to go through menopause and live for decades after they have finished breeding.[73][74] Killer whales are unique among cetaceans, as their heads become shorter as they age.[62]
Females breed until age 40, meaning on average they raise five offspring. The lifespans of wild females average 50 years, with a maximum of 80–90 years.[75] 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.[75] 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,[76] but this method of age determination is now believed to be inaccurate for older animals.[77] One male known to researchers in the Pacific Northwest (identified as J1) was estimated to have been 59 years old when he died in 2010.[78] Captive killer whale lifespans are typically significantly shorter, usually less than 25 years; however, numerous individuals are alive in their 30s, and a few have reached their 40s.
Range and habitat
A killer whale bursts forward out of the water. Its head is just starting to point downward, and is about a body width above the surface.
A killer whale leaps out of the water when swimming—a behaviour known as porpoising
Killer whales are found in all oceans and most seas. Due to their enormous range, numbers, and density, distributional estimates are difficult to compare,[81] but they clearly prefer higher latitudes and coastal areas over pelagic environments.[82]
Systematic surveys indicate the highest densities of killer whales (>0.40 individuals per 100 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.[81] 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.[81] Information for offshore regions and tropical waters is more scarce, but widespread, if not frequent, sightings indicate the killer whale can survive in most water temperatures. They have been sighted, for example, in the Mediterranean, the Arabian Sea, the Gulf of Mexico and the Indian Ocean around the Seychelles.[81]
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.[83]
Migration patterns are poorly understood. Each summer, the same individuals appear off the coasts of British Columbia and Washington. 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.[84] Resident killer whales sometimes travel as much as 160 km (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 mi (160 km) up the Columbia River in the United States.[85][86] They have also been found in the Fraser River in Canada and the Horikawa River in Japan.[85]
Population
Worldwide population estimates are uncertain, but recent consensus suggests an absolute minimum of 50,000.[2][32] 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.[87] Japan's Fisheries Agency estimated 2,321 killer whales were in the seas around Japan.[88][89]
Feeding
A skeleton is suspended on metal framework, which incorporates an outline of the soft tissue along a median cross-section of the animal. The jaws host many sharp teeth, and pectoral fin bones are attached to the lower ribs. The backbone stretches away out of frame; no hind limb bones can be seen. The outline includes an upright dorsal fin and rounded forehead.
A killer whale skeleton
Killer whales hunt varied prey; however, different populations or species tend to specialize and some can have a dramatic impact on certain prey species.[90] 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. About 65% of them are large, fatty Chinook.[91] Chum salmon are also eaten, but smaller sockeye and pink salmon are not a significant food item.[92] 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.[93]
Killer whales are apex predators, meaning that they themselves have no natural predators. They are sometimes called the wolves of the sea, because they hunt in groups like wolf packs.[94]
Each population seems to prefer one kind of prey. Those that feed on whales may not even recognize fish as food. This specialization in diet and hunting, combined with small differences in markings, suggest that they might be different species, rather than populations. Advanced methods that sequenced the entire mitochondrial genome revealed systematic differences in DNA between different populations.
