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Orca

2007 Schools Wikipedia Selection. Related subjects: Mammals

           iOrca

                    Fossil range: Early Pliocene - Recent

   A male orca with its characteristic tall dorsal fin swims in the waters
   near Tysfjord, Norway
   A male orca with its characteristic tall dorsal fin swims in the waters
   near Tysfjord, Norway
   Size comparison against an average human
   Size comparison against an average human

                             Conservation status

   Conservation dependent (LR/cd)
                          Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Mammalia
   Order:    Cetacea
   Suborder: Odontoceti
   Family:   Delphinidae
   Genus:    Orcinus
   Species:  O. orca

                                Binomial name

   Orcinus orca
   Linnaeus, 1758
   Orca range (in blue)
   Orca range (in blue)

   The Orca or Killer Whale (Orcinus orca) is the largest species of the
   oceanic dolphin family ( Delphinidae). They are sometimes referred to
   as blackfish, a group including pilot whales, pygmy and false killer
   whales, and melon-headed whales. It is the second-most widely
   distributed mammal on Earth (after humans) and is found in all the
   world's oceans, from the frigid Arctic regions to warm, tropical seas.
   It is also a versatile predator, eating fish, sea turtles, seabirds,
   pinnipeds, elasmobranchs, sirenians and even other cetaceans. This puts
   the orca at the pinnacle of the marine food chain.

   Orcas are marine mammals with a fearsome reputation that goes as far
   back as Pliny the Elder's description of the species. The name "killer
   whale" reflects the animal's habit of attacking whales, and does not
   mean that orcas are a threat to humans. Aside from a boy who was
   charged (but not grabbed) while swimming in a bay in Alaska, there have
   been no confirmed attacks on humans in the wild. There have, however,
   been isolated reports of captive orcas attacking their handlers at
   marine theme parks.

Nomenclature

   The name "orca" (plural "orcas") was originally given to these animals
   by the ancient Romans, possibly borrowed from the Greek word ὄρυξ which
   (among other things) referred to a species of whale. The term "orc" (or
   its variant "ork") has been used to describe a large fish, whale or
   sea-monster. It is now considered an obsolete equivalent for "orca."

   The name "killer whale" is widely used in common English. However,
   since the 1960s, "orca" has steadily grown in popularity as the common
   name to identify the species, and both names are now used. The species
   is called orca in most other European languages, and, as there has been
   a steady increase in the amount of international research on the
   species, there has been a convergence in naming.

   A pod of orcas is capable of killing a large whale. It is commonly
   thought that 18th-century Spanish sailors dubbed these creatures
   asesina-ballenas, or "whale killer" for this reason. However, this
   title was improperly translated into English as "killer whale". The
   term became so prevalent that Spanish speakers commonly used its
   retranslation of ballena asesina.

   There are still many, especially in the research community, who prefer
   the original name, believing it to be an appropriate description of a
   species that does indeed kill many animals, including other cetaceans.
   These supporters of the original name point out that the naming
   heritage is not limited to Spanish sailors. Indeed the genus name
   "Orcinus" means "from Hell" (see Orcus), and although the name "orca"
   (in use since antiquity) is probably not etymologically related, the
   assonance might have given some people the idea that it means "whale
   that brings death," or "demon from hell."

   The name of this species is similarly intimidating in many other
   languages. In Finnish and in Dutch it is called miekkavalas and
   zwaardwalvis respectively, which means "sword whale". To the Haida
   people native to the islands of Haida Gwaii off the coast of British
   Columbia, the animal was known as skana or "killing demon". The
   Japanese call them shachi (鯱), whose kanji character combines the
   radicals for fish (魚) and tiger (虎).

   A former name for the species is grampus. This is now seldom used and
   should not be confused with the Grampus genus (containing Risso's
   Dolphin).

Taxonomy and evolution

   The orca skull.
   Enlarge
   The orca skull.

   The orca is the sole species in the genus Orcinus. It is one of
   thirty-five species in the dolphin family. Like the Sperm Whale genus
   Physeter, Orcinus is a genus with a single, abundant species with no
   immediate relatives from a cladistic point of view, thus
   paleontologists believe that the orca is a prime candidate to have an
   anagenetic evolutionary history — that is the evolution of ancestral to
   descendant species without splitting of the lineage. If true, this
   would make the orca one of the oldest dolphin species, although it is
   unlikely to be as old as the family itself, which is known to date back
   at least five million years.

   However, there are are at least three types of orcas that are
   genetically distinct enough to be considered different subspecies or
   races. These classifications are based mostly on research performed off
   the west coast of Canada and the United States.
   Female and male resident orca fins, J or K pod, Washington coast, July
   2006
   Enlarge
   Female and male resident orca fins, J or K pod, Washington coast, July
   2006

   The three types are:
     * Resident: These are the most commonly sighted of the three
       populations in the coastal waters of the northeast Pacific. The
       resident orcas' diet consists primarily of fish, and they live in
       complex and cohesive family groups known as pods. Female residents
       characteristically have a rounded dorsal fin tip that terminates in
       a sharp corner. They are known to visit certain areas consistently.
     * Transient: The diet of these orcas consists almost exclusively of
       marine mammals. They do not eat fish. Transients generally travel
       in small groups, usually of two to six animals. Unlike residents,
       transients may not always stay together as a family unit. Female
       transients are characterized by dorsal fins that are more
       triangular and pointed than those of residents.
     * Offshore: These orcas cruise the open oceans and feeding primarily
       on fish, sharks and turtles. They have been seen traveling in
       groups of up to 60 animals. Currently there is little known about
       the habits of this population, but they can be distinguished
       genetically from the residents and transients. Female offshores are
       characterized by dorsal fin tips that are continuously rounded.

   Transient and resident orcas live in the same areas but generally
   ignore each other. The name "transient" originated from the belief that
   these whales, which are often seen in groups of three or four, were
   outcasts from larger resident pods. Researchers later discovered that
   transients are an entirely different community. Recent genetic research
   has found that the types have not interbred for up to 10,000 years
   (Chadwick).

   An additional two or three orca types have recently been documented in
   the Antarctic. Type A looks like a typical orca, living in open water
   and feeding mostly on minke whales. Type B and type C whales are
   smaller than type A. Both B and C types have grayish and light yellow
   skin in place of the usual black and white orca colouring; B and C
   types can also be distinguished from each other through variations in
   colour pattern. They live close to the Antarctic ice pack, with type B
   whales feeding mostly on seals, and type C on fish.

Physical characteristics

   Dorsal fin and saddle patch of an orca, most likely a resident female
   Enlarge
   Dorsal fin and saddle patch of an orca, most likely a resident female
   A female and her calf
   Enlarge
   A female and her calf

   Orcas are distinctively marked, with a black back, white chest and
   sides, and a white patch above and behind the eye. They have a heavy
   and stocky body and a large dorsal fin with a dark gray "saddle patch"
   at the fin's rear. Males can be up to 9.5 m long (31 ft) and weigh in
   excess of 6 tons; it has been reported that especially large males have
   reached nearer 8 tons. Females are smaller, reaching up to 8.5 m (28
   ft) and a weight of about 5 tons. The longest orca ever recorded was a
   male from Washington state, measuring 9.8 m (32 ft). Calves at birth
   weigh about 180 kg and are about 2.4 m long (8 ft). The orca's large
   size and strength make them one of the fastest marine mammals, often
   reaching speeds in excess of 35mph.

   Unlike most dolphins, the pectoral fin of an orca is large and rounded
   — more of a paddle than other dolphin species. Males have significantly
   larger pectoral fins than females. At about 1.8 m (6 ft), the dorsal
   fin of the male is more than twice the size of the female's, and is
   more of a triangle shape — a tall, elongated isosceles triangle,
   whereas the dorsal fin of the female is shorter and generally more
   curved. Nicks, cuts and scrapes on these fins, as well as distinctive
   features of each fin, help scientists identify individuals.

   Large male orcas are very distinctive and are unlikely to be confused
   with any other sea creature. When seen from a distance in temperate
   waters, females and juveniles can be confused with various other
   species, such as the false killer whale or Risso's dolphin.

   Most life history data about orcas has been obtained from long-term
   surveys of the population off the coasts of British Columbia and
   Washington and by monitoring captive orcas. Due to the completeness of
   the study and highly structured nature of the pods in this population,
   the information is detailed and accurate; however, transient groups and
   groups in other oceans may have slightly different characteristics.
   Females become sexually mature at around 15 years of age. From then
   they have periods of polyestrous cycling with non-cycling periods of
   between three and sixteen months. The gestation period varies from
   fifteen to eighteen months. Mothers calve, with a single offspring,
   about once every five years. In analysed resident pods, birth occurs at
   any time of year, with the most popular months being those in winter.
   Newborn mortality is very high — one survey suggested that nearly half
   of all calves fail to reach the age of six months. Calves nurse for up
   to two years, but will start to take solid food at about twelve months.
   Cows breed until the age of 40, meaning that on average they raise five
   offspring. Typically, females live to the age of fifty, but may survive
   well into their eighties or nineties in exceptional cases. Males become
   sexually mature at the age of 15, but do not typically reproduce until
   age 21. Males live to about 45 on average, and close to 90 in
   exceptional cases.

Range

   The orca is the second-most widely distributed mammal in the world,
   after the human. They are found in all oceans and most seas, including
   (unusual for cetaceans) the Mediterranean and Arabian seas. Cooler
   temperate and polar regions are preferred, however. Although sometimes
   spotted in deep water, coastal areas are generally preferred to pelagic
   environments.

   The orca is particularly highly concentrated in the northeast Pacific
   Basin, where Canada curves into Alaska, off the coast of Iceland and
   off the coast of northern Norway. They are regularly sighted in
   Antarctic waters right up to the ice-pack and are believed to venture
   under the pack and survive breathing in air pockets like the beluga
   does. In the Arctic, however, the species is rarely seen in winter, as
   it does not approach the ice pack. It does visit these waters during
   summer.

   Information for off-shore regions and tropical waters is more scarce
   but widespread, if not frequent; sightings indicate that the orca can
   survive in most water temperatures. Sightings are rare in Indonesian
   and Philippine waters. No estimate for the total worldwide population
   exists. Local estimates include 70-80,000 in the Antarctic, 8,000 in
   the tropical Pacific (although tropical waters are not the orca's
   preferred environment, the sheer size of this area — 19 million square
   kilometres — means there are thousands of orcas), up to 2,000 off
   Japan, 1,500 off the cooler northeast Pacific and 1,500 off Norway.
   Adding very rough estimates for unsurveyed areas, the total population
   could be around 100,000.

Diet

   When swimming quickly, orcas sometimes leap out of the water.
   Enlarge
   When swimming quickly, orcas sometimes leap out of the water.

   The orca is an apex predator, and the array of species on which orcas
   prey is extremely diverse. Specific populations show a high degree of
   specialization on particular prey species. For example, some
   populations in the Norwegian and Greenland sea specialise in herring
   and follow that fish's migratory path to the Norwegian coast each
   autumn. Other populations in the area prey on seals. On average, an
   orca eats 500 lbs. (227 kg) of food each day.

Fish and other cold-blooded prey

   Fish-eating populations of orcas prey on 30 species of fish,
   particularly salmon (including Chinook and Coho), herring, and tuna.
   Basking sharks, oceanic whitetip sharks, and occasionally even great
   white sharks are taken for their nutrient-rich livers. Cephalopods,
   such as octopuses and a wide range of squids, are also targets.

   While salmon are usually hunted by a single orca or a small group of
   individuals, herring are often caught using carousel feeding: the orcas
   force the herring into a tight ball by releasing bursts of bubbles or
   flashing their white undersides. The orcas then slap the ball with
   their tail flukes, either stunning or killing up to 10-15 herring with
   a successful slap. The herring are then eaten one at a time. Carousel
   feeding has only been documented in the Norwegian orca population and
   with some oceanic dolphin species.

Warm-blooded prey

   The orca is the only cetacean species to regularly prey on other
   cetaceans. Twenty-two species have been recorded as preyed on, either
   through an examination of stomach contents, examining scarring on the
   prey's body, or from observing the orcas' feeding activity. Groups of
   orcas will even prey on larger cetaceans such as minke whales, gray
   whales, female and juvenile sperm whales or young blue whales. A group
   of orcas take a young whale by chasing it and its mother through the
   sea, wearing them out. Eventually the orcas manage to separate the pair
   and surround the young whale, preventing it from returning to the sea's
   surface to breathe. Large whales are typically drowned in this manner.
   Pods of female sperm whales can sometimes protect themselves against a
   group of orcas by forming a protective circle around their calves with
   their flukes facing outwards. This formation allows them to use their
   powerful flukes to repel the orcas.

   Other marine mammals, including most species of seal and sea lion, are
   preyed upon by Orcas. Walrus and sea otters are hunted less frequently.
   Several species of bird are also preyed upon, including penguins,
   cormorants and sea gulls. Sea lions are killed by head-butting or by
   being slapped and stunned by a tail fluke.

   A captive orca in Friendship Cove discovered that it could regurgitate
   fish onto the surface, attract sea gulls, and eat them. Other orcas
   then learned the behaviour by example. Orcas at Sea World California
   have also been observed hunting birds.

   There has also been one recorded case of probable orca cannibalism. A
   study carried out by V. I. Shevchenko in the temperate areas of the
   South Pacific in 1975 recorded two male orcas whose stomachs contained
   the remains of other orcas. Of the 30 orcas captured and examined in
   this survey, 11 had empty stomachs — an unusually high percentage which
   indicates the orcas were forced to cannibalism through a lack of food.

   Orcas use complex hunting strategies to find and subdue their prey.
   They will occasionally throw seals through the air in order to stun and
   kill them. Often, to avoid injury, they will 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.

   More specialized feeding techniques are used by various populations
   around the world. In Patagonia, and the Iles Crozet in the Indian
   Ocean, orcas feed on South American sea lion and elephant seal pups in
   shallow water; even to the extent of purposely stranding themselves
   (temporarily). Orcas will spy-hop to locate seals resting on ice floes,
   and then create a wave to wash over the floe, causing the seal to be
   thrown into the water where a second orca waits to kill it. This
   behaviour has only been recorded a few times and it is not known how
   often it occurs. The most recent recorded instance in April 2006 ended
   with the group of orcas returning the seal to the ice floe once they
   had shown the younger animals how to properly perform the technique.

Behaviour

   Orcas often raise their body out of the water in a behaviour called
   spyhopping.
   Enlarge
   Orcas often raise their body out of the water in a behaviour called
   spyhopping.

   The day-to-day behaviour of orcas is generally divided into four
   activities: foraging, travelling, resting and socializing. Orcas are
   generally enthusiastic in their socializing, engaging in behaviours
   such as breaching, spyhopping, and tail-slapping. All-male groups often
   interact with erect penises. Whether this interaction is part of play
   or a display of dominance is not known.

   Resident orcas can also be seen swimming with porpoises, other dolphins
   and sea lions, which are common prey for transient orcas. Resident
   orcas are continually on the move, sometimes traveling as much as 100
   miles (160 km) in a day, but may be seen in a general area for a month
   or more. Range for resident orca pods may be as much as 800 miles
   (1300 km) or as little as 200 miles (320 km). Unlike residents,
   transients often travel and hunt in silence.

Social structure of resident orca communities

   Fish-eating orcas in the North Pacific have a complex system of social
   grouping. Unlike any other mammal population whose social structure is
   known, resident orcas of both sexes live with their mothers for their
   entire lives. The basic unit is the matriline, which consists of a
   single female (the matriarch) and her descendants. The sons and
   daughters of the matriarch form part of the line, as do the sons and
   daughters of those daughters (the sons and daughters of the sons join
   the matriline of their mates) and so on down the family tree.

   Because females can live for up to ninety years, it is not uncommon for
   four or even five generations to travel together. These matrilineal
   groups are highly stable over many years. Individuals will only split
   off from their matrilineal group for up to a few hours at a time in
   order to mate or forage. No permanent casting out of an individual from
   a matriline has ever been recorded. The average matriline size as
   recorded in northeast Pacific waters is nine animals.

   Matrilines form loose aggregations called pods, consisting on average
   of about 18 animals. Members of a pod all have the same dialect (see
   the section on vocal behaviour below) and consist of closely related
   matriline fragments. Unlike matrilines, pods will split apart for days
   or weeks at a time in order to carry out foraging before joining back
   together. The largest recorded pod is 49 animals. Orcas within a pod do
   not interbreed; mating occurs only between members of different pods.

   Resident pods are generally larger than the transient and offshore
   pods, having up to 50 or more members. Several pods occasionally join
   to form what are referred to as superpods, sometimes numbering in
   excess of 150 animals.

   The next level of grouping is the clan. A clan consists of those pods
   which have a similar dialect. Again the relationship between pods
   appears to be genealogical, consisting of fragments of families with a
   common heritage on the maternal side. Different clans can occupy the
   same geographical area; pods from different clans are often recorded
   traveling together. When resident pods come together to travel as a
   clan, they greet each other by forming two parallel lines akin to a
   face-off before mingling with each other.

   The final layer of association, perhaps more arbitrary and devised by
   humans rather than the other very natural divisions, is called the
   community and is loosely defined as the set of clans that are regularly
   seen mixing with each other. Communities do not follow discernible
   familial or vocal patterns.

   In the northeast Pacific, three communities of fish-eating orcas have
   been identified:

          + The southern community (1 clan, 3 pods, 90 orcas as of 2006)
          + The northern community (3 clans, 16 pods, 214 orcas as of
            2000)
          + The south Alaskan community (2 clans, 11 pods, 211 orcas as of
            2000)

   It should be emphasized that these hierarchies are valid for resident
   groups only. Transient groups are generally smaller because, although
   they too are based on matrilines, some male and female offspring
   eventually disperse from the maternal group. However, transient groups
   still have a loose connection defined by their dialect.

Vocal behaviour

   Orcas, like this one spotted near Alaska, commonly breach, often
   lifting their entire body out of the water.
   Orcas, like this one spotted near Alaska, commonly breach, often
   lifting their entire body out of the water.

   As with other dolphins, orcas are very vocal animals. They produce a
   variety of clicks and whistles that are used for communication and
   echolocation. The vocalization types vary with activity. While resting
   they are much quieter, merely emitting an occasional call that is
   distinct from those heard when engaging in more active behaviour.

   Fish-eating resident groups of orcas in the Northeast Pacific tend to
   be much more vocal than transient groups living in the same waters.
   Resident orcas feed on fish, particularly Pacific salmon, a prey with
   poor underwater hearing that cannot detect orca calls at any
   significant distance. Transient orcas on the other hand feed mainly on
   marine mammals and occasionally on seabirds. Because all marine mammals
   have excellent underwater hearing, transients probably remain silent
   for much of the time to avoid detection by their acoustically-sensitive
   prey. They sometimes use a single click (called a cryptic click) rather
   than the long train of clicks observed in other populations.

   Resident pods have group-specific dialects. Each pod has its own vocal
   repertoire or set of particular stereotyped underwater calls (call
   types). Every member of the pod seems to know all the call types of the
   pod, so it is not possible to identify a single animal using voice
   alone. A particular call type might be used by only one group or shared
   among several.

   The number of call types shared by two groups appears to be a function
   of their genealogical relatedness rather than their geographical
   distance. Two groups that share a common set of ancestors but have
   grown apart in distance are likely to have a similar set of call types,
   indicating that calls are a learned behaviour.

Orcas and humans

   Although only scientifically identified as a species in 1758, the orca
   has been known to humans since prehistoric times. The desert culture of
   the Nazca created a Nazca line presumably representing an orca
   (although it could be any whale) sometime between 200 BC and AD 600.

   The first description of an orca is given in Pliny the Elder's Natural
   History (written circa 70 AD). The aura of invincibility around the
   all-consuming orca was well-established by this time. Having observed
   the public slaughter of a whale stranded at a harbour near Rome, Pliny
   writes, "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."

Hunting

   Orcas swimming in Prince William Sound off the Alaskan coast.
   Enlarge
   Orcas swimming in Prince William Sound off the Alaskan coast.

   Orcas were targeted in commercial whaling for the middle part of the
   twentieth century once stocks of larger species had been depleted.
   Commercial hunting of orcas came to an abrupt halt in 1981 with the
   introduction of a moratorium on all whaling. (Although from a taxonomic
   point of view an orca is a dolphin rather than a whale, it is
   sufficiently large to come under the purview of the International
   Whaling Commission.)

   The greatest hunter of orcas was Norway, which took an average of 56
   animals per year from 1938 to 1981. Japan took an average of 43 animals
   from 1946 to 1981. (War year figures are not available but are likely
   to be fewer). The Soviet Union took a few animals each year in the
   Antarctic, with the extraordinary exception of the 1980 season when it
   took 916.

   Today, no country carries out a substantial hunt. Japan usually takes a
   few individuals each year as part of its controversial program of
   scientific research as specified in IWC constitution. A similarly small
   level of subsistence whaling is carried out by Indonesia and Greenland.
   As well as being hunted for their meat, orcas have also been killed
   because of competition with fishermen. In the 1950s the United States
   Air Force, at the request of the Government of Iceland, used bombers
   and riflemen to slaughter orcas in Icelandic waters because they
   competed with humans for fish. The operation was considered a great
   success at the time by fishermen and the Icelandic government. However,
   many were unconvinced that orcas were responsible for the drop in fish
   stocks, blaming overfishing by humans instead. This debate has led to
   repeated studies of North Atlantic fish stocks, with neither side in
   the whaling debate giving ground since that time.

   Orcas are also occasionally killed out of fear of their reputation. No
   human has ever been attacked by an orca in the wild, but sailors in
   Alaska shoot the animal occasionally out of concern for their own
   lives. This fear has generally dissipated in recent years due to better
   education about the species, including the appearance of orcas in
   aquariums and other aquatic attractions.

Co-operating with humans

   More unusually, orcas have also been known to co-operate with humans in
   the hunting of whales. One famous incidence of this was near the port
   of Eden in South-Eastern Australia in the 1920s. A pod of orcas, led by
   a dominant male called Old Tom, would assist whalers in hunting baleen
   whales. The orcas would find the target whales, shepherd them into
   Twofold Bay and then alert the whalers to their presence and often help
   to kill the whales. In return the whalers allowed the orcas to eat the
   tongue and lips of the whale before hauling it ashore.

Captivity

   The orca's intelligence, trainability, striking appearance, playfulness
   in captivity and sheer size have made it a popular exhibit at aquariums
   and various aquatic theme parks. The first orca capture and display
   occurred in Vancouver in 1964. Over the next 15 years around 60 or 70
   orcas were taken from Pacific waters for this purpose. In the late
   1970s and the first half of the 1980s, orcas were generally taken from
   Icelandic waters (50 in the five years to 1985). Since that time, orcas
   have been successfully bred in captivity and wild specimens are
   considerably rarer. Orcas in captivity may develop pathologies such as
   dorsal fin collapse, seen in 60-90% of captive males.
   Shamu posing at Seaworld, San Diego
   Enlarge
   Shamu posing at Seaworld, San Diego

   Several theories exists as to why the dorsal fin collapse occurs,
   namely that the cartilage that holds the fin erect is not yet strong
   enough to support the fin when the orca is placed in captivity. The
   hardening of the cartilage occurs in late adolescence, in which the
   orca spends much time in deep ocean waters, and it is theorized that
   the pressure the water exerts on the fin allows it to remain supported
   while the cartilage hardens. In captivity, however, the tank the whales
   reside in lack sufficient water pressure to produce this effect, and
   the fin collapses before the cartilage that would support it in nature
   solidifies. Another theory exists that states that the whale is almost
   always in a state of turning in a tank, since it is not large enough to
   allow swimming in one direction for any normal duration. The constant
   turning exerts pressure on the dorsal fin, which in turn causes it to
   collapse.

   There have been incidents with orcas in captivity attacking humans. In
   1991, a group of 3 orcas (Haida, Nootka, and Tillikum) killed a trainer
   named Keltie Byrne at Sealand in Victoria, British Columbia (where
   employees were not allowed in the water with orcas), the orcas
   apparently not knowing Byrne could not survive underwater. After this,
   and due to Tilikum being bullied by the two females in the tank, Tilly
   (as he is nicknamed) was relocated to SeaWorld of Orlando, Florida,
   where he remains. He is currently the largest orca in captivity.

   In 1999, at the SeaWorld park in Orlando, Florida,Tilikum killed a man
   who snuck into his tank after hours. . The man was found naked and
   draped over the orca's back the next morning. In late July 2004, during
   a show at the SeaWorld park in San Antonio, Texas, an orca pushed its
   trainer of ten years underwater and barred the way to the rim of the
   pool; the trainer could only be rescued from the animal after several
   minutes.

   One of the more infamous incidents involving orca aggression took place
   in August 1989, when a dominant female orca, Kandu V, struck a newcomer
   orca, Corky II, with her mouth during a live show. Corky II had been
   imported from Marineland California just months prior to the incident.
   According to reports, a loud smack was heard across the stadium.
   Although trainers tried to keep the show rolling, the blow severed an
   artery near Kandu V's jaw, and she began spouting blood. The crowd was
   quickly ushered out, and after a 45-minute hemorrhage, Kandu V died.
   Opponents of these shows see these incidents as supporting their
   criticism.

   SeaWorld continued to be under criticism from the Born Free Foundation
   over its continued captivity of the orca Corky II, who they want
   returned to her family, the A5 Pod, a large pod of orcas in British
   Columbia, Canada .

   Orcas in captivity have vastly reduced life expectancies, on average
   only living into their 20s. In the wild, females may live into their
   80s. The captive environment also bears no resemblance to their wild
   habitat, and the social groups that the orcas are put into are
   completely foreign to those found in the wild . Critics claim that
   captive life is stressful due to small tanks, false social groupings
   and chemically-altered water. Organisations such as the WSPA and the
   Whale and Dolphin Conservation Society campaign against the captivity
   of orcas.

   The captive orca Namu developed a bacterial infection which damaged his
   nervous system, causing him to become non-responsive to people. During
   his illness he charged full speed into the wire mesh of his pen,
   thrashed violently for a few minutes and then died. A semi-documentary
   was named after him.

Environmental threats

   The Exxon Valdez oil spill had an adverse effect on orcas in Prince
   William Sound and the Kenai Fjords region of Alaska. One resident pod
   was caught in the spill; though the pod successfully swam to clear
   water, eleven members of the pod (about half) disappeared in the
   following year. The spill had a long-term effect in reducing the amount
   of available prey, such as salmon, and has thus been responsible for a
   local population decline. In December 2004, scientists at the North
   Gulf Oceanic Society said that the AT1 transient population of orcas,
   now only numbering 7 individuals, has failed to reproduce at all since
   the spill. This population is expected to become extinct. Sightings
   Newsletter report on AT1 pod.

   Like other animals at the highest trophic levels of the food chain, the
   orca is particularly susceptible to poisoning via accumulation of
   Polychlorinated biphenyls (PCBs) in the body. A survey of animals off
   the Washington coast found that PCB levels in orcas were higher than
   those in harbour seals in Europe that have been sickened by the
   chemical. Samples from the blubber of orcas in the Norwegian Arctic
   show higher levels of PCBs, pesticides and brominated flame-retardants
   than in Polar bears. However, no direct evidence of sickness in orcas
   has been found. The most likely effect, if any, would be a reduced rate
   of reproduction or decreased ability to fight off disease
   (immunodepression). In 2005, the United States government listed the
   Southern Resident population of orcas as an endangered species under
   the Endangered Species Act (ESA) due to deterioration of the three pods
   which spend most of the year in the Georgia and Haro Straits and Puget
   Sound in British Columbia and Washington state.

   Heavy ship noise can interfere with the acoustic communication and
   echolocation of orcas. In the mid-1990s, loud underwater noises from
   salmon farms were used to deter seals. Orcas subsequently avoided the
   surrounding waters.

   Orcas are popular object of whale watching, which may change orca
   behaviour and stress orcas, particularly if boats approach orcas too
   closely or block their line of travel.

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