Orca 13b Download 2021
Jerry Bradley
The orca (Orcinus orca), or killer whale, is a toothed whale that is the largest member of the oceanic dolphin family. It is the only extant species in the genus Orcinus. Orcas are recognizable by their black-and-white patterned body. A cosmopolitan species, orcas are found in diverse marine environments, from Arctic to Antarctic regions to tropical seas.
The International Union for Conservation of Nature assesses the orca's conservation status as data deficient because of the likelihood that two or more orca 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 human fisheries. In late 2005, the southern resident orcas, which swim in British Columbia and Washington waters, were placed on the U.S. Endangered Species list.
Orcas are not usually a threat to humans, and no fatal attack has ever been documented in their natural habitat. There have been cases of captive orcas killing or injuring their handlers at marine theme parks. Orcas feature strongly in the mythologies of indigenous cultures, and their reputation in different cultures ranges from being the souls of humans to merciless killers.
The genus name Orcinus means "of the kingdom of the dead",[8] or "belonging to Orcus".[9] Ancient Romans originally used orca[10] (pl. orcae) for these animals, possibly borrowing Ancient Greek ὄρυξ (óryx). This word referred (among other things) to a whale species, perhaps a narwhal.[11] As part of the family Delphinidae, the species is more closely related to other oceanic dolphins than to other whales.[12]
Orcinus orca is the only recognized extant species in the genus Orcinus, and one of many animal species originally described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae.[14] Konrad Gessner wrote the first scientific description of an orca in his Piscium & aquatilium animantium natura of 1558, part of the larger Historia animalium, based on examination of a dead stranded animal in the Bay of Greifswald that had attracted a great deal of local interest.[15]
The orca is one of 35 species in the oceanic dolphin family, which first appeared about 11 million years ago. The orca lineage probably branched off shortly thereafter.[16] Although it has morphological similarities with the false killer whale, the pygmy killer whale and the pilot whales, a study of cytochrome b gene sequences indicates that its closest extant relatives are the snubfin dolphins of the genus Orcaella.[17] However, a more recent (2018) study places the orca as a sister taxon to the Lissodelphininae, a clade that includes Lagenorhynchus and Cephalorhynchus.[18] In contrast, a 2019 phylogenetic study found the orca to be the second most basal member of the Delphinidae, with only the Atlantic white-sided dolphin (Leucopleurus acutus) being more basal.[19]
The three to five types of orcas may be distinct enough to be considered different races,[20] subspecies, or possibly even species[21] (see Species problem). 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."[3] Although large variation in the ecological distinctiveness of different orca groups complicate simple differentiation into types,[22] research off the west coast of North America has identified fish-eating "residents", mammal-eating "transients" and "offshores".[23] Other populations have not been as well studied, although specialized fish and mammal eating orcas have been distinguished elsewhere.[24] Mammal-eating orcas in different regions were long thought likely to be closely related, but genetic testing has refuted this hypothesis.[25]
Orcas 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).[28] Orcas may attain larger sizes as males have been recorded at 9.8 m (32 ft) and females at 8.5 m (28 ft).[29] Calves at birth weigh about 180 kg (400 lb) and are about 2.4 m (7.9 ft) long.[30][31] The skeleton of the orca is typical for an oceanic dolphin, but more robust.[29]
With their distinctive pigmentation,[29] adult orcas are seldom confused with any other species.[32] When seen from a distance, juveniles can be confused with false killer whales or Risso's dolphins.[33] The orca typically has a sharply contrasted black-and-white body; being mostly black on the upper side and white on the underside. The entire lower jaw is white and from here, the colouration stretches across the underside to the genital area; narrowing between the flippers then widening some and extending into lateral flank patches close to the end. The tail fluke (fin) is also white on the underside, while the eyes have white oval-shaped patches behind and above them, and a grey or white "saddle patch" exists behind the dorsal fin and across the back.[29][34] Males and females also have different patterns of black and white skin in their genital areas.[35] In newborns, the white areas are yellow or orange coloured.[29][34] Antarctic orcas may have pale grey to nearly white backs.[32] Some Antarctic orcas are brown and yellow due to diatoms in the water.[21] Both albino and melanistic orcas have been documented.[29]
Orca pectoral fins are large and rounded, resembling paddles, with those of males significantly larger than those of females. Dorsal fins also exhibit sexual dimorphism, with those of males about 1.8 m (5.9 ft) high, more than twice the size of the female's, with the male's fin more like an elongated isosceles triangle, whereas the female's is more curved.[36] In the skull, adult males have longer lower jaws than females, as well as larger occipital crests.[37] The snout is blunt and lacks the beak of other species.[29] The orca's teeth are very strong, and its jaws exert a powerful grip; the upper teeth fall into the gaps between the lower teeth when the mouth is closed. The firm middle and back teeth hold prey in place, while the front teeth are inclined slightly forward and outward to protect them from powerful jerking movements.[38]
Orcas 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 the water by emitting clicks and listening for echoes,[39] as do other members of the dolphin family. The mean body temperature of the orca is 36 to 38 C (97 to 100 F).[40][41] Like most marine mammals, orcas have a layer of insulating blubber ranging from 7.6 to 10 cm (3.0 to 3.9 in) thick beneath the skin.[40] The pulse is about 60 heartbeats per minute when the orca is at the surface, dropping to 30 beats/min when submerged.[42]
An individual orca 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 orcas to be counted each year rather than estimated, and has enabled great insight into life cycles and social structures.[43]
In the Antarctic, orcas 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. However, orcas are merely seasonal visitors to Arctic waters, and do not approach the pack ice in the summer. With the rapid Arctic sea ice decline in the Hudson Strait, their range now extends deep into the northwest Atlantic.[47] Occasionally, orcas swim into freshwater rivers. They have been documented 100 mi (160 km) up the Columbia River in the United States.[48][49] They have also been found in the Fraser River in Canada and the Horikawa River in Japan.[48]
Fish-eating orcas prey on around 30 species of fish. Some populations in the Norwegian and Greenland sea specialize in herring and follow that fish's autumnal migration to the Norwegian coast. Salmon account for 96% of northeast Pacific residents' diet, including 65% of large, fatty Chinook.[64] Chum salmon are also eaten, but smaller sockeye and pink salmon are not a significant food item. Depletion of specific prey species in an area is, therefore, cause for concern for local populations, despite the high diversity of prey.[51] On average, an orca eats 227 kilograms (500 lb) each day.[65] While salmon are usually hunted by an individual whale or a small group, 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. They then slap the ball with their tail flukes, stunning or killing up to 15 fish at a time, then eating them one by one. Carousel feeding has only been documented in the Norwegian orca population, as well as some oceanic dolphin species.[66] Some dolphins recognize fish eating orcas (usually resident) as harmless and remain in the same area.[67]
In New Zealand, sharks and rays appear to be important prey, including eagle rays, long-tail and short-tail stingrays, common threshers, smooth hammerheads, blue sharks, basking sharks, and shortfin makos.[68][69] With sharks, orcas may herd them to the surface and strike them with their tail flukes,[68] while bottom-dwelling rays are cornered, pinned to the ground and taken to the surface.[70] In other parts of the world, orcas have preyed on broadnose sevengill sharks,[71] small whale sharks[72] and even great white sharks.[71][73] Competition between orcas and white sharks is probable in regions where their diets overlap.[74] The arrival of orcas in an area can cause white sharks to flee and forage elsewhere.[75][76] Orcas appear to target the liver of sharks.[71][73]
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