Species Spotlight: Northeast Pacific Orca Ecotypes

Orcas (Orcinus orca) are one of the first animals that drew me to marine biology as a child. They swam through many of the marine sciences library books I obsessed over. They were the mascot of my childhood swim team. Everything about them is iconic, from their distinct coloration to their fascinating behaviors.

Orcas are found across the globe, in distinct populations each with different learned behaviors. These populations are referred to as ecotypes.

While previously viewed as one, globally-distributed species, recent taxonomic debate casts doubt on whether the ecotypes are simply subspecies or if these ecotypes should be classed as distinct species.

The northeast Pacific Ocean is a hotspot for orca research, even though the whale occurs globally. As a result, these populations are very well-studied.

Acrylic marker illustration of an orca (O. orca), created by me. ©LivInSeas, 2026

Northeast Pacific Ecotypes:

Resident orcas (Orcinus orca ater):

The North Pacific’s resident killer whales are broken up into several subpopulations. These include the Southern Residents (including the famous J, K, and L pods), Northern Residents, and Southern Alaska Residents.

Resident killer whales diet on fish. Northern and Southern resident populations prefer to mostly eat salmon. Due to salmon migration patterns, this means that they share a food source.

However, as salmon migrate south from Alaskan waters, Northern Residents are able to exploit the food source first. Both populations of orcas also have to contest with prey shortages driven by anthropogenic impacts, such as commercial fishing efforts and habitat loss.

Southern Alaska resident populations also dine on salmon, but they include other fish in their diets as well. Even during seasons where salmon are abundant, these orcas will supplement their diets with Pacific halibut, arrowtooth flounder, and sablefish.

Resident killer whales have extremely stable matrilineal social structures. Offspring of both sexes live with their mothers for their entire lives. Dispersal from these groups is extremely rare.

Resident killer whales have vocal dialects which are distinct to maternal groups. Additionally, they are able to visually and acoustically recognize close maternal kin. While this helps facilitate outbreeding, it does not identify paternal kin.

The distinct subpopulations of resident killer whales typically do not associate with each other. However, scientists have documented occasional interbreeding.

Three resident orcas hunting a salmon. NOAA Fisheries, Public domain, via Wikimedia Commons.

Bigg’s/Transient Orcas (Orcinus orca rectipinnus):

Bigg’s orcas, more commonly known as transient orcas, occupy a broader range than residents. They can be found from Southern California up to the Arctic Circle.

Bigg’s orcas prey primarily on marine mammals, such as seals, sea lions, and other cetaceans. They occasionally feed on seabirds as well.

Within populations of Bigg’s orcas, males maintain strong social bonds with their mothers throughout their entire lives. However, females tend to disperse from the group after having at least one calf, following reductions in close social associations with their mother.

Bigg’s killer whales have higher levels of genetic diversity compared to resident killer whales. While both groups tend to form large groups for the purpose of outbreeding, the higher frequency of dispersal from the natal group in Bigg’s orcas likely reduces inbreeding.

While the ranges of transient orcas and residents overlap, the groups seem to actively avoid each other. Similar to the resident orcas, subpopulations of Bigg’s orca also seem to stay somewhat isolated from one another. However, scientists have noted occasional gene flow between the inner West Coast transient population and the southeastern Alaska transient population.

Scientists have proposed that Bigg’s orcas and resident orcas are separate species from Orcinus orca, based on genetic data. However, for the time being, they are still considered subspecies of Orcinus orca.

Offshore Orcas:

Offshore killer whales, like residents, are piscivores. Their diet is comprised on fish, and they may specialize in feeding on sharks.

Far less is known about the social structures of offshore orcas compared to the other northeastern Pacific groups. They have been observed in groups of 20-75, but larger groups up to 200 whales have also been spotted.

Offshore orcas have a greater range than the other northeast Pacific ecotypes, and generally occur 15 kilometers (9 miles) or more offshore.

They also seem to be genetically distinct from other orca populations, and are the smallest of the northeast Pacific ecotypes.

A southern resident orca showing off its acrobatic skills, slapping the water with its fluke. National Marine Sanctuaries, Public domain, via Wikimedia Commons.

Fun fact: Orcas are dolphins, and they’re also whales! Orcas, as well as other dolphins (Family: Delphinidae) are part of the Parvorder Odontoceti. The Odontocetes are the “toothed whales” (Odont – Greek for “tooth”, Cetus – Latin for “whale”, derived from the Ancient Greek “Kêtos“).

Odontoceti includes sperm whales, river dolphins, oceanic dolphins, and porpoises. Which, by definition, are all considered to be whales, along with the baleen whales (Mysticeti).