Two Types Of Orcas Are Actually Two Separate Species, Scientists Argue

For a long time, orcas (or killer whales) were all believed to be one species but with different “ecotypes” in various regions, but scientists have now identified at least two distinct species in the North Pacific Ocean. They argue there are enough differences to declare the Bigg’s killer whales and resident killer whales separate species. This discovery was based on a suite of information, including morphological, behavioral, acoustic, genetic, and other data.

The wolf or wolves of the ocean?

In 1758, Carl Linnaeus, the grandfather of species classification, described killer whales as a single species – Delphinus orca – which was later moved to the genus Orcinus. From then on, various scientists have claimed to have identified other species of the iconic and easily recognizable marine mammal (they are actually the largest member of the dolphin family, just to complicate things) that roam and ravage the world’s oceans. However, many of these claims were based on single skeletons, which have been insufficient for scientists to accept more broadly. 

Then, in the 1860s, a Californian whaling captain called Charles Melville Scammon (a name worthy of the sea) produced a manuscript describing several large marine mammals that he had seen during his voyages. Among the entries were orcas, which Scammon referred to as “the wolves of the ocean”, which, he eloquently wrote, lived “by violence and plunder.” 

According to his observations, killer whales could be separated into two species, one that had tall, sharp dorsal fins (which he called high-finned orcas) and one that had shorter, blunt dorsal fins (low-finned orcas). 

After compiling his descriptions, Scammon sent them for review to Edward Drinker Cope, the infamous Secretary of the Smithsonian Institute who is better known today for his involvement in the ridiculous dinosaur Bone Wars

Examples of the illustrations Scammon included in his manuscript. It is not clear whether he drew them himself or they were created by someone following his descriptions. (A) shows O. ater, () shows O. rectipinnus
Image credit: Morin et al, 2024, Royal Society Open Science.

True to his character, Cope ended up editing and then publishing Scammon’s manuscript without his permission (though he did credit the whaling captain for his descriptions). According to his changes, the tall-finned whales were named to be named Orca rectipinna (Latin for “erect wing”), and the shorter-finned ones were called Orca ater (Latin for “black”).

Despite their efforts, it is likely Scammon and Cope got it wrong in many ways. They may have merely described differences between male and female orcas (the former are known to have taller, sharper-looking dorsal fins while the latter have shorter, blunter ones). However, it seems they were on the right track. 

The differences are more than fin deep 

Over the centuries, regional differences in various characteristics have led to the recognition of several sub-forms of orcas that are separated into “types” and “ecotypes”, rather than separate species. The factors here include the animals’ body size, color, patterning, social structure, vocalization patterns, and foraging strategies. 

In the North Pacific, there are three known ecotypes. The Bigg’s (or sometimes ‘transient’) orca, so-called resident orcas, and Offshore orca. Each one has its own individual characteristics related to its distribution, preferred habitat, and diet. For instance, Bigg’s orcas are most commonly observed on the continental shelf in temperate to Arctic waters. They prefer to feed on other marine mammals, including seals and whales, whereas resident orcas prefer coastal waters in the eastern Pacific, and tend to eat fish, especially salmon. 

The Offshore orcas, on the other hand, primarily live in waters off the continental shelf and are far more mysterious than the other two. But they are known to hunt fish, including elasmobranchs (cartilaginous fish, such as sharks, rays, skates, and sawfish). 

For some time, biologists have increasingly taken notice of key differences between Bigg’s and resident orcas. In addition to their differing diets, residents tend to move in tight-knit family pods, while Bigg’s prefer to roam in smaller groups. 

They’re the most different killer whales in the world, and they live right next to each other and see each other all the time. They just don’t mix.

In the 1970s, the Canadian scientist Michael Bigg noticed that the killer whales that ended up with his name did not mix with their residential counterparts. This is typically a sign of two different species. But now researchers from National Oceanic and Atmospheric Administration Fisheries (NOAA) and universities have confirmed Bigg’s suspicions – they are indeed two different species. 

“We started to ask this question 20 years ago, but we didn’t have much data, and we did not have the tools that we do now,” Phil Morin, an evolutionary geneticist at NOAA Fisheries’ Southwest Fisheries Science Center said in a statement. “Now we have more of both, and the weight of the evidence says these are different species.”

The results from genetic data show that the two species probably diverged around 300,000 years ago and emerged from opposite ends of the orca family tree. Subsequent genomic research confirmed that they evolved as genetically and culturally distinct groups that just happen to occupy similar waters. 

“They’re the most different killer whales in the world, and they live right next to each other and see each other all the time,” said Barbara Taylor, a former NOAA Fisheries marine mammal biologist who was part of the science panel that assessed the status of Southern Residents. “They just do not mix.”

The proposed names for these two species of orcas are now being based on the original names offered by Scammon and Cope. If their proposals are accepted by the Taxonomy Committee of the Society of Marine Mammalogy later this year, then the Bigg’s orcas will become Orcinus rectipinnus, while the resident orcas will be known as Orcinus ater.

While orcas are among the most widespread mammals in the world, second only to humans, there are still many mysteries surrounding them. It is likely that, in the near future, we will see the identification of other killer whale species. These may well include the so-called “Type D” orcas that have been seen in the Southern Ocean around Antarctica. 

The paper is published in the Royal Society Open Science

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