Orcas and their ecotypes

There are many factors that ensure that every orca ecotype remains separate. The main reason is reproductive isolation. Orcas from different regions feed on different foods, communicate in different languages, interact only with each other and have even evolved into distinct groups that play different roles in the ecosystem. Many ecotypes are even subdivided into sub-populations!

A number of species can be broken down into ecotypes, or subspecies. Scientists use this term when the group or population is genetically adapted to its environment. Even if they are moved, animals of a subspecies will retain their distinctive traits.

The Earth is constantly changing. When a new habitat becomes available, speciation — when two populations become different species — occurs. The ancestors of modern orcas adopted these different habitats and specialized to make the most of them. Though they may look similar at first glance, certain traits make them quite distinct, both in terms of form and function.

In an earlier study, scientists argue that the transient clade in the North Pacific separated ∼700,000 years ago, which would have been much earlier than what the previous study mentioned. This date is more generally accepted, but several studies propose that the divergence occurred between 700,000 and 350,000 years ago. A separate secondary diversification event occurred between the Antarctic and Atlantic species. The authors explain that the Atlantic species (Types 1 and 2) are more closely related to each other than with the Antarctic ones (those in the southern hemisphere).

Within the Antarctic species, Type 1 diverged earlier, and Resident and Offshore species share the most recent common ancestor. This paper, along with more recent ones, further argues that due to their strong genetic differences, the transient and the Pacific resident ecotypes (Orcinus rectipinnus and Orcinus ater, respectively) deserve species status.

Many populations have specialized hunting techniques that are unique to their needs and geographical location. For instance, wave washing, a technique whereby orcas hunting in packs will create waves to knock seals into the water, has been observed multiple times in orcas in Antarctica. Another example of specialized feeding found more recently describes how transient orcas would surround their prey and take turns ramming or hitting it. If it was a small prey, like a sea lion or a seal, they would sometimes toss it into the air, shake it by the fins, or even drown it. Once the prey was dead, they would share their spoils. For larger prey, such as grey whale calves, the matriarch would direct the pod to separate the mother from its calf before ramming, biting and drowning the calf. For as many different types of prey that orcas have, there are more hunting techniques that exist.

There are two communities of resident killer whales in British Columbia: northern and southern residents. With less than 75 remaining individuals according to a census from December 2023, the southern resident killer whale is on the brink of extinction. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated the species as endangered in 2001. The Species at Risk Act (SARA) has listed the species as endangered under Schedule 1 (i.e. species that are extirpated, endangered, threatened, and of special concern) since 2003. The main threats that they face include contaminants in their natural environment, a decline in the availability of Chinook salmon (their main prey), and physical and acoustic disturbances.