Orcinus orca, commonly known as the “orca” or “killer whale”, is the largest dolphin in the cetacean family. They are the most widespread cetacean, present in every ocean across the world, and represented in varied habitats. There are several ‘subtypes’ of orca, which some scientists suggest may be separate species or subspecies. Certain populations or subtypes are considered threatened or endangered due to varying factors, such as food scarcity, human threat, and pollution; the Southern Resident population are classified as Endangered under the ESA, and the AT1 Transient Stock is classified as depleted under the MMPA. All orca populations are protected under the MMPA, although the Southern Resident is the only endangered population. There are an estimated 50,000 orca worldwide.

Taxonomically, orca are a part of Delphinidae – while Delphinidae as a group diverged from the rest of Odotoceti approximately 12-15mya, Orcinus are thought to have diverged shortly after. Phylogenetic placement of the species is under some debate, but the most recent studies suggest that Orcinus is one of the most basal Delphinidae species. There are two recognised extinct genera in Orcinus: O. citoniensis and O. paleorca. These species were both smaller than O. orca, suggesting that they slowly evolved to eat bigger and bigger prey.

Orca are the largest extant member of Delphinidae. While exact sizes can vary depending on ‘type’, on average males are 6-8 meters long and 6 tonnes, and females are 5-7 meters long and 3-4 tonnes. The largest recorded size for males is 9.8m and 10t, and for females is 8.5m. Calves are around 2.4m at birth. Males have larger dorsal fins than females – while the dorsal of the female is generally gently curved and about 91cm tall, male dorsals are tall and straight, sometimes reaching 1.8m in height. Orca reach sexual maturity between 10 and 18 years of age, and females can continue breeding until their 40s. Orca are one of the few species besides humans that go through a menopause and live past their reproductive prime – this is theorised to be because orca engage in communal care, and elder females play an important role in teaching and supporting new mothers. Females live on average between 50-80 years in the wild, with the eldest (J2 Granny) being around 80. Males live between 29-60 years in the wild, and often die along with their mothers.

Orca are easily recognised by their stark black and white pigmentation; the back and flank are mostly black, with a white underbelly that extends across the entire lower jaw, and up the flank in lateral patches. Iconically, they also have a white ‘eye patch’ – an oval patch of white situated just above and behind both eyes. There is also generally a lighter grey patch behind the dorsal fin, called a ‘saddle patch’. Both the eye patches and saddle patches are important for identification, both of ‘types’, and of individuals. Newborn orca can often appear orange or yellow tinted over their white markings, but this fades as they grow. Some types of Antarctic orca may have yellow tinting to their white markings, and this is thought to be due to diatoms in the water where they live.


An orca breaching


An orca surfacing for breath

Orca markings

A pod of orca swimming underwater

A pod of orca rubbing against pebbles


There are three main ‘types’ of orca recognised in the North Hemisphere, mostly defined by their diet and lifestyle.

‘Resident’ orca stay in a regular territory, generally near coasts, and have a fish-based diet with occasional squid. The most famous Resident population are the Southern Residents (SRKW), which consists of the J, K and L pods, but there are also the Northern Resident (NRKW), Southern Alaskan Resident, and Western Alaska North Pacific Resident populations. Salmon is the preferred food source of the NRKW and SRKW, with the Southern Residents preferring specifically Chinook salmon; their depleted populations contribute to the problems facing the SRKW.

‘Transient’ orca travel over much wider ranges and are almost exclusively mammal hunters. These orca share some of the same ranges as the Resident populations in the North Atlantic, however the two groups do not interact and avoid each other. Transients can be distinguished from Residents by their solid grey saddle patches, and the more triangular dorsal fins of the females. Three “stocks” of Transients are recognised; the AT1 stock, GOA/AI/BS stock, and West Coast stock. AT1 is considered ‘depleted’ after being affected by the Exxon Valdez oil spill.

‘Offshore’ orca have lifestyles and appearances somewhat similar to Residents, with notable differences including their diet (consisting of mostly schooling fish, as well as sharks and potentially some mammals) and habitat (open water, as opposed to the Resident’s coastal ranges). They have not been observed and studied as much as Transients and Residents, but they are known to be genetically distinct. Offshore orca are generally smaller than Transients or Residents, and females have a much more rounded dorsal fin.

There are many other subtypes of orca, and their diversity is thought to be massive. As well as the Resident, Transient and Offshore populations, NOAA recognises a Hawaii stock and a Gulf of Mexico stock which seem to be generally unrelated to the others. North Atlantic Type 1 orca are generalists, observed in Norway, Scotland, and Iceland. North Atlantic Type 2 orca are open-ocean mammal hunters. In the Southern Hemisphere, there are several types of ‘Antarctic’ orca recognised: Type A, Type B1, Type B2, Type C, and Type D.