虎鲸不见了英文

TaxonomyThe genus Orcinus is considered to be monospecific, with a single species: O. orca. A second species, O. rectipinna, the Pacific killer whale, has been suggested, but is nowadays not considered to be a valid species (Duffield, 1986). Also O. nanus and O. glacialis have been suggested for a dwarf form of killer whale in the Antarctic, but also these species are considered invalid.AppearanceKiller whales are robust animals. Males grow to 6.7 -8.2 m (maximum 9.5 m) and weigh 3,600-5,400 kg). Females are smaller at 5.2-7.3 m and they weigh 1,400-3,600 kg) (Fad, 1996). The head has a characteristic bulbous melon. The flippers are highly mobile and rounded, looking like large paddles. In males, these flipper can measure 2x1.2 m. The most striking feature is the large dorsal fin. It is tall ( 1.8 m or more) and triangular in males and may even be curved slightly forward. In juveniles, the dorsal fin is smaller and falcate (sickle-shaped).The coloration is basically black dorsally and white ventrally. There is a grey "saddle" just behind the dorsal fin, a white patch behind the eye and a white or greyish intrusion on the side above the genital region. There is a lot of variation on the color and shape of the saddle and this can potentially be used for identification of individuals.DistributionKiller whales are true cosmopolitans and can be found in virtually all oceans and major seas. Usually they are found within 800 km from the coast. They occur in groups of 1 to 70-100 animals. Most studies have been done on the resident population in British Columbia and on the North Atlantic population. In the Eastern North Atlantic they are seen along the coast and also pelagically. Occassionally there are strandings and/or sightings in the Baltic Sea, the North Sea and the Mediterranean.Social structureFemale killer whales become sexually mature at 4.6-4.9 m in length (age 8 years) and males at 5.8 m (age 15 years). Physical maturity is attained at 20-25 years. Maximum longevity is at least 35 years.For the BC population, Olesiuk et al (1990) report the following data: The mean life expectancy for females is 50.2 years (translates to an Annual Survival Rate (ASR) of 0.98). Their first viable calf is born at an age of 14.9 years. The maximum longevity is 80-90 years. Most births occur between October and March. Neonate mortality is fairly high at 43%. Males have a mean life expectancy of 29.2 years (ASR=0.966). They become sexually mature at 15 years and physically mature at 21 years. The maximum longevity is about 50-60 years.FeedingThe killer whale is an opportunistic feeder and that is reflected in the wide spectrum of prey species on its diet. It included a range of marine mammals, such as large baleen whales, including the blue whale and the humpback whale (Flórez-González, 1994), beaked whales, dolphins, porpoises, pinnipeds (seals, sea lions, elephant seals and walruses) and sea otters. There is also some evidence for cannibalism in killer whales. The diet also includes a large number of fish species, including sharks, herring, cod, capelin, halibut, mackerel, salmon and tuna. The killer whale also takes marine birds, especially penguins, and turtles as well as squid and octopus. See Hoyt (1990) for an extensive overview, with full references, of the killer whale diet.