Orca (Orcinus orca)

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Orca in the Ross Sea

The orca (Orcinus orca), also known as the killer whale, is the largest member of the dolphin family and the top predator in the ocean. They are found in all oceans, from the polar regions to the tropics, and have a varied diet and culture depending on their population and ecotype. Some populations of killer whales are endangered or depleted due to human activities, such as hunting, overfishing, pollution, and noise disturbance.

Description

Orcas are mostly black on top with white undersides and white patches near the eyes. They also have a gray or white saddle patch behind the dorsal fin. These markings vary widely between individuals and populations. Adult males develop disproportionately larger pectoral flippers, dorsal fins, tail flukes, and girths than females.

Types

Orca types. Credit to NOAA Southwest Fisheries Science Center.

Orcas have a cosmopolitan distribution and several distinct populations or types have been documented or suggested. Three to five types of orcas may be distinct enough to be considered different races, subspecies, or possibly even species. 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.".

In the eastern North Pacific Ocean, there are three distinct types of orcas recognized—transient, resident, and offshore. Residents live close to shore in large pods of about 10 to 20 individuals and feed primarily on fish.

Offshore orcas are similar to residents but are distinguished by their smaller overall size and rounded, nicked fins.

Behaviour

Killer whales are highly social, and most live in social groups called pods (groups of maternally related individuals seen together more than half the time) where they hunt together and share responsibility for raising young and taking care of the sick or injured. Individual whales tend to stay in their natal pods. Pods typically consist of a few to 20 or more animals, and larger groups sometimes form for temporary social interactions, mating, or seasonal concentrations of prey.

Killer whales rely on underwater sound to feed, communicate, and navigate. Pod members communicate with each other through clicks, whistles, and pulsed calls. Each pod in the eastern North Pacific possesses a unique set of calls that are learned and culturally transmitted among individuals. These calls maintain group cohesion and serve as family badges.

Communication

Orcas communicate through pulsed calls and whistles, which form a unique dialect for a family. They express their identity through their cultural habits, and their prey choices are central to this, and so it shapes their language. Orca language is learned and inherited, and just like human babies, orcas can hear their mother in the womb, and so they’re learning their family’s language before they’re born.

The Southern Resident killer whales’ language is so sophisticated that it contains three distinct dialects, one for each of the pods—J, K, and L—with vocalizations that are unique to each pod. However, some calls are common across all three pods, facilitating communication across the community, which allows them to socialize, bond, and mate with other pod members.

Diet

Orcas have a diverse diet, although individual populations often specialise in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as seals and other species of dolphin. Their diet consists of chinook and coho salmon, herring, halibut, rockfish, and mackerel.

Killer whale pods have eating habits comparable to the individual food cultures of different countries. Variation in diets across pods is very common, even when they live in the same habitat, as each pod learns a different set of hunting behaviors that dictate what prey they catch and eat.

Hunting

Orcas are precise and efficient hunters that use different strategies depending on their prey and region. They feed on over 140 species, including great white sharks, which they rip open for their livers and hearts¹. They can flip the sharks over to induce a state of paralysis and make them easy to eat. They can also come ashore to hunt seals and sea lion pups, hiding their dorsal fins and beaching themselves.

Some Antarctic orcas use the cunning tactic of regularly hunting in packs and making waves to wash seals off floating ice. These hunting techniques are almost ritualistic and are passed down from generation to generation.

Distribution and habitat

Killer whales are found in all oceans15. While they are most abundant in colder waters like Antarctica, Norway, and Alaska, they are also found in tropical and subtropical waters16. The most well-studied killer whale populations occur in the eastern North Pacific Ocean17. Resident killer whales have been seen from California to Russia19. Offshore killer whales have the largest range of any community, and often occur more than 9 miles offshore20. They are not, however, exclusively “offshore”, as they are sometimes seen in coastal nearshore waters21. Transient killer whales also occur throughout the eastern North Pacific, and are often seen in coastal waters18. Their habitat sometimes overlaps with Resident and Offshore killer whales22.

Reproduction and lifespan

The average lifespan for male killer whales is about 30 years, but they can live up to at least 60 years23. Females typically live about 50 years, but can live up to at least 90 years in the wild24.

Females reach sexual maturity when they are between 10 and 13 years old25. They are typically pregnant for 15 to 18 months and give birth to a single calf26. Calves nurse exclusively for at least a year, but remain in close association with their mother for the first two years27. There is no distinct calving season, so birth can take place in any month28. The birth rate for killer whales is not well understood. In some populations, birth rate is estimated at every 5 years for an average period of 25 years29. Killer whales, beluga whales, narwhals, short-finned pilot whales, and humans are the only known species that go through menopause30.

Conservation status

All killer whales are protected under the Marine Mammal Protection Act (MMPA) in the United States. Only two populations receive additional special protections under federal law:

• Southern Resident Distinct Population Segment (listed as endangered under the Endangered Species Act)
• AT1 Transient stock (designated as depleted under the MMPA).

Threats

• Entanglement in fishing gear
• Prey depletion
• Chemical contamination
• Oil spills
• Noise disturbance

Captivity

Wanda the first captive orca

Orcas have been captured from the wild for display in captive facilities since the 1960's. The first orca to be captured in 1961 was found off the coast of California and given the name Wanda. Many orcas are held in captivity for breeding or performance purposes. They soon became popular attractions at public aquariums and aquatic theme parks due to their intelligence, trainability, striking appearance, playfulness, and sheer size.

The practice of keeping orcas in captivity is harmful to the animals due to the separation from their familial pod during capture, and their living conditions and health in captivity.

See also

• Cetacean entanglements
• List of deceased captive orcas
• List of living captive orcas
• Category:Orca (videos)

External links

• Killer Whale NOAA