The Orca or Killer Whale (Orcinus orca) is the largest member of the oceanic dolphin family Delphinidae. They are sometimes referred to as blackfish, a group including pilot whales, pigmy 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, deadly predator, eating fish, turtles, birds, seals, sharks and even other juvenile and small cetaceans. This puts the orca at the pinnacle of the marine food chain. Orcas have been known to attack massive baleen whales, in particular gray and Blue whales.
The name “killer whale” reflects the animal’s reputation as a magnificent and fearsome sea mammal that goes as far back as Pliny the Elder’s description of the species. Today it is recognized that the orca is a dolphin rather than a whale and that it is not a danger 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.
The name “orca” (plural “orcas”) was originally given to these animals by the ancient Romans, possibly borrowed from the Greek word á½„ÏÏ…Î¾ which (among other things) referred to a species of whale.
The term “orc” (or its variant “ork”) has historically 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 – leading to confusion. 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.
Taxonomy and evolution
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 palaeontologists believe that the killer whale 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.
Three distinct populations
Modern research indicates that there are three distinct population types or classifications of orcas off the western coastline of North America. While each looks similar, they have distinct genetic differences, food preferences, and habits. These are the called the transient, resident and offshore types.
Transient orcas generally travel in small groups, usually up to 7 or 8 animals. Unlike residents, transients may not always stay together as a family unit. Transients are often seen cruising along the shorelines hunting for prey, which commonly includes seals, porpoises, and sea lions. Female transients are characterized by dorsal fins that are pointier than those of residents. Male transients often have scarred dorsal fins, probably from injuries resulting from hunting and killing prey. Unlike residents, transients often travel and hunt in silence. The range for transient killer whales is from southeast Alaska to California.
Resident orcas are the most commonly sighted of the populations, often observed in coastal waters. Female residents characteristically have a rounded dorsal fin tip that terminates in a sharp corner. While nomadic, their range is much smaller, and they are known to visit certain areas consistently. The resident orca’s diet consists primarily of fish, including salmon and herring and they frequent areas where their preferred fish are abundant. They are continually on the move, sometimes traveling as much as 100 miles in a day, but may be seen in a general area for a month or more. Resident orcas live in complex and cohesive family groups known as pods. Resident pods are generally larger than the transient and offshore pods, having up to 50 or more members.
Offshore orcas were given this name for what the name implies. They remain offshore cruising the open oceans feeding primarily on fish. 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.
The animals 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” behind it. Males can be up to 31 ft (9.5 m long) and weigh in excess of 6 tons; females are smaller, reaching up to 28 ft (8.5 m) and a weight of about 5 tons. Calves at birth weigh about 396 pounds (180 kg) and are about long 8 ft (2.4 m). Unlike most dolphins, the pectoral fin of an orca is large and rounded – more of a paddle than other dolphin species. Pectoral fins of males are significantly larger than those of 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. There are also minor variations in physical characteristics between resident and transient Killer Whales.
Females become 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 analyzed resident pods, birth occurs at any time of year, with the most popular months being those in winter. New-born 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 30 on average, and to 50 in exceptional cases.