Orcinus orca, or simply orca, is in fact the largest of the dolphins, a member of the family of Oceanic Dolphins, within the order of cetaceans. This species of marine mammal is also commonly known as the killer whale, is easily identified by the black and white colouration; the underside is white and there are white patches behind the eyes, and a greyish white area called a saddle-patch behind the dorsal fin. The shape of the saddle is unique in each animal, and can help to identify individuals. The dorsal fin is also used to recognise individuals. Male orcas have the tallest dorsal fin known in the animal kingdom, measuring up to six feet high in mature males (IUCN. 2008). Females have shorter, more curved dorsal fins.

Orca exhibiting porpoising behaviour. Source: Minette Layne

Size comparison of an average human and an Orca. Source: Chris Huh/Wikipedia

Conservation Status:  Data Deficient

Scientific Classification Kingdom: Anamalia (Animals) Phylum:--- Chordata Class:------ Mammalia (Mammals) Order:-------- Cetacea (Cetaceans) Family:-------- Delphinidae    Genus:----------Orcinus Species:----------- Orcinus orca (Linnaeus, 1758)

Common names: Atlantic killer whale Botskop Killer Killer whale Killer-trasher Orca Orka Pacific killer whale Sword grampus Swordfish grampus

Physical description

Killer whales have streamlined, black and white bodies. They are black on the dorsal surface, white extends from the bottom of the chin to just beyond the anus on the ventral surface. There is also a white spot above the eye. In both sexes there is a saddle spot which is a grey spot behind the dorsal fin on the back. In calves, their black is somewhat grey up to a year old. Also, the white on the calf's underside has a yellow tint to it until they reach one year old. The average length for a male adult is 8 metres, with the maximum length at 9.75 m. The average length in females is 7 m with a maximum length of 8.5 m. Newborn calves are from 2.0 to 2.4 m long and weigh about 136 kilogram at birth. The average weight for a male killer whale is 7200 kg. Female average body size and weight is slightly smaller than that of males. In males, the erect dorsal fin can reach up to 1.8 m high; in females and immature males this dorsal fin is only about 0.9 m high. This fin curves over either to the right or left side. (Estes et al., 2006; Heintzelman, 1981; Mann et al., 2000; Watson, 1981) 

Reproduction

Killer whales are polygynandrous; both males and females have multiple mates throughout a season or a lifetime. (Mann et al., 2000; Payne, 1995; Robeck et al., 2004)  While killer whales are difficult to study in the wild, some of their reproductive habits have been recorded and studied in captive whales.

Killer whales can reproduce whenever females enter estrus, which can occur mutiple times a year. However, most breeding takes place in the summer, and killer whales are typically born in the fall. Females reach sexual maturity between 6 and 10 years of age. Males reach sexual maturity between 10 and 13 years old. Female killer whales begin to mate between 14 and 15 years of age. The youngest female whale on record to give birth was 11 years old. Females have a calf every 6 to 10 years and they stop breeding around the age of 40. The result is four to six offspring over a 25 year span. (Estes et al., 2006; Mann et al., 2000; Robeck et al., 2004; Watson, 1981) 

Gestation takes about 14 months, although a gestation length in captivity was recorded at 539 days. Killer whales have a single calf at a time, twins have only been recorded once. Newborn calves nurse for about a year before weaning. Some studies show that almost half of all newborn calves die before their first birthday. (Estes et al., 2006; Mann et al., 2000; Robeck et al., 2004; Watson, 1981) 

Killer whale females invest a lot of energy in raising their offspring. They carry the calf for almost a year and a half, then give birth and nurse for another 12 months. During that time, mothers teach their calves to hunt and include their offspring in the social network of their pods. Because these animals are not monogamous, it is assumed that the fathers exhibit no parental involvement after mating.

When a killer whale calf is born into a pod, it relies on its mother for nutrition and support. Calves remain in their natal pod after independence. (Estes et al., 1998; Mann et al., 2000; Robeck et al., 2004; Slijper, 1979) 

Lifespan

Killer whale mortality rate varies with the age of the animal. Neonatal mortality is very high, and, in captivity, neonatal mortality is between 37% and 50%. The reason for these high mortality rates is unknown, but predation is not considered a primary threat during this time. After six months, mortality rates steadily decline as killer whales learn how to protect and nourish themselves. Mortality rates are said to be the lowest around 12 to 13 years in males and 20 years in females.

The average lifespan for a female in the wild is around 63 years, with a maximum of 80 to 90 years. Male life expectancy is a bit shorter, with the average lifespan being around 36 years, with a maximum of 50 to 60 years. (de Magalhaes, Costa, and Toussaint, 2005; Mann et al., 2000) 

Behavior

Killer whales are highly social, and their social structure is complex. They travel in pods which can contain several to as many as 50 individuals. There has even been reports of hundreds of individuals in one pod, but this was a temporary association between a group of smaller pods. Individuals in pods are generally multiple generations of related individuals and made up of about 20% mature males, 20% calves, and 60% females and immature males. Killer whales have limited dispersal from the maternal pod and young whales are always part of their mother's pod. Individuals in pods swim within 100 meters of each other and coordinate their activities. They may share prey and rarely leave the pod for more than a few hours. Killer whales teach pod members through apprenticeship. Skill in hunting and parenting are among the skills taught to younger whales. (Mann et al., 2000; Matthews, 1978)

Home range size is unknown, but some studies have shown that killer whales live with their pods together in their home range for many years. While home range size is unknown, they have been documented to swim up to 160 km a day. (Mann et al., 2000; Matthews, 1978) 

Orcas are the top predator in the sea and have an extremely broad diet, including fish, gulls, penguins, turtles, squid and marine mammals, even including large whales such as grey and blue whales. They spend their life in stable groups, called pods, which hunt co-operatively (6). Long-term studies off Canada have shown that orcas occur as transient, resident or offshore populations, which have different hunting styles and social organisation. Orcas are extremely active and acrobatic; the species is one of the fastest marine animals and often breach (clear the water), lobtail (slap tail flukes on the surface of the water), and spy-hop (bring the head out of the water). Females become sexually mature in their teens and produce a single calf every three years until they reach around 40 years of age. After the gestation period of up to 17 months, calves are suckled for about a year. Killer whales live to between 50 and 100 years of age (6). 

There are no known adverse effects of Orcinus orca on humans. Only one valid instance has been recorded when a killer whale attacked a human. 

Distribution

Orcinus orca is found living in all oceans of the world, and hence considered a cosmopolitan species. They have been spotted from as far north as the Artic Ocean near pack ice to as far south as the Antarctic Ocean. Although Orcinus orca seems to prefer colder waters, they have also been observed in tropical waters. There seems to be no or very little migration due to weather and water temperature, but killer whales will move to other areas when food becomes scarce. (Estes et al., 2006; Ford, Ellis, and Balcomb, 2000; Heintzelman, 1981; Mann et al., 2000)

Habitat

Killer whales live in aquatic marine habitats, including both offshore and coastal waters. They are found in every ocean of the world. Normally prefering depths of 20 to 60 m, killer whales also visit shallow waters along coastlines or dive to 300 m in search of food. Killer whales generally occupy the same home range year round. (Estes et al., 2006; Heintzelman, 1981; Mann et al., 2000; Norris, 2002; Slijper, 1979) 

Predation

Killer whales have no natural predators, although young killer whales may be attacked by other killer whales or large sharks. They are at the top of the marine food chain. Humans sometimes prey on killer whales, but not in great numbers. 

Ecosystem roles

Orcas are the top predator in the sea and have an extremely broad diet, including fish, gulls, penguins, turtles, squid and marine mammals, even including large whales such as grey and blue whales  

Food habits

Killer whales are exceptionally successful predators. Orcinus orca diet is difficult to study and is most frequently assessed through looking at stomach contents. They eat a wide variety of large prey cluding: Phocidae, Otariidae, smaller Odontoceti, Actinopterygii, Chondrichthyes, Sepidae, Octopoda, Cheloniidae, sea birds, Enhydra lutris, Lutrinae, and other animals.

Killer whales eat on average 45 kg of food a day, but they can eat much more than that. They swallow small prey whole, but tend to tear up larger prey before consumption. Killer whales are social hunters, as are Canis lupus and Panthera leo. They often hunt in packs and use coordinated social behavior and communication to hunt prey larger than themselves, such as larger Cetacea.(Heintzelman, 1981; Mann et al., 2000; Watson, 1981) 

Conservation status

The Orca is classified on the IUCN Red list as Data Deficient; moreover, in the USA, the Orca has been listed as an endangered species. This marine mammal appears on Appendix II of the CITES site, which means they are not immediately threatened by extinction, but conservation efforts are required to keep them from reaching an extinction vortex. Killer whales have been less directly impacted by human exploitation as some other whale species. They are occasionally hunted but management of harvests has been used as a conservation tool.

Threats

Killer whales are top predators in most marine ecosystems and impact the populations of common prey, such as Phocidae and Otariidae in breeding areas. Killer whales are host to some endoparasites and ectoparasites. They are host to killer whale lice (Cyamus orcini), trematodes (Fasciola skiranini), cestodes (Trigonocotyle spasskyi), and nematodes (Anasakis simplex). 

Toxoplasmosis (Toxoplasma gondii) is a frequently studied disease that affects killer whales. While this parasite is often benign, it can have serious and fatal effects. (Chadwick, 2001; Endoh et al., 2004; Estes et al., 1998; Heyning and Dahlheim, 1988; Mann et al., 2000) 

The orca is threatened by hunting, prey depletion, and exposure to human activities such as disturbance from boats including whale-watching crafts, particularly when they venture closer to shore (Deeke et al. 2005). As it is the top predator it is particularly vulnerable to contaminants, which build up in the tissues of prey species and subsequently affect the predator (Heintzelman. 1981). Furthermore, the captivity industry has posed a threat, taking live individuals for the aquarium trade (Bower. 2000). 

Killer whales are hunted and used for a number of things. In various parts of the world, they are used for oil and meat. Meat is sold for human consumption or used for fertilizer or bait.  

References

• Encyclopedia of Life: Orca
• IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
• Bower, B. 2000. Culture of the Sea. Science News, Vol. 158, Iss.18: 284-286
• Chadwick, D. 2001. Evolution of Whales. National Geographic, Vol. 200 Issue 5: 64-78.
• Deeke, V., J. Ford, P. Slater. 2005. The Vocal Behaviour of Mammal-Eating Killer Whales: Communicating with costly calls. Animal Behaviour, 69/2: 385-405.
• Estes, J., D. Demaster, D. Doak, T. Williams, R. Brownell, Jr.. 2006. Whales, Whaling, and Ocean Ecosystems. Berkely and Los Angeles, California; London, England: University of California Press.
• Ford, J., G. Ellis, K. Balcomb. 2000. Killer Whales. University of Washington Press, 104.
• Heintzelman, D. 1981. A World Guide to Whales, Dolphins, and Porpoises. Tulsa, Oklahoma 74101: Winchester Press.
• Mann, J., R. Connor, P. Tyack, H. Whitehead. 2000. Cetacean Societies: Field Studies of Dolphins and Whales. Chicago, Illinois: The University of Chicago Press, Chicago 60637
• Miller, P. 2006. Diversity in Soundpressure Levels and Estimated Active Space of Resident Killer Whale Vocalizations. Journal of Comparative physiology, 192: 449-459.
• Murata, K., K. Mizuta, K. Imazu, F. Terasawa, M. Taki, T. Endoh. 2004. The Prevalence of Toxoplasma gondii Antibodies in Wild and Captive Cetaceans from Japan.. The Journal of Parasitology, 90: 896-898.
• Norris, S. 2002. Creatures of Culture? Making the Case for Cultural Systems in Whales; and Dolphins. Bioscience, vol. 52, no. 1: 9-14.
• Northwest Atlantic Ocean species (NWARMS)
• Payne, R. 1995. Among Whales. New York, New York 10020: Charles Scribner's Sons.