April 13, 2024

Two types of orcas are actually two distinct species, scientists argue

For a long time, it was believed that orcas (or killer whales) were 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 that there are enough differences to declare Bigg’s killer whales and resident killer whales as separate species. This discovery was based on a set of information, including morphological, behavioral, acoustic, genetic and other data.

The wolf or the ocean wolves?

In 1758, Carl Linnaeus, the grandfather of species classification, described orcas as a unique species – Delphinus orca – which was later transferred to the genus orcinus. Since then, several scientists have claimed to have identified other species of the iconic and easily recognizable marine mammal (they’re actually the largest member of the dolphin family, just to complicate matters) that roam and ravage the world’s oceans. However, many of these claims have been based on single skeletons, which have been insufficient for scientists to accept more widely.

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

According to his observations, orcas could be separated into two species, one that had tall, sharp dorsal fins (which he called high-finned orcas) and another 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 Institution, best known today for his involvement in the ridiculous Dinosaur Bone Wars.

Examples of the illustrations Scammon included in his manuscript. It is unclear whether he designed them himself or whether they were created by someone following his descriptions. (Sample O. after() shows O. retipinus

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 (although he gave credit to the whaling captain for his descriptions). According to his changes, high-finned whales were named to be named retipine orca (Latin for “erect wing”), and those with shorter fins were called Orca after (Latin for “black”).

Despite their efforts, it is likely that Scammon and Cope erred in several 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 dorsal fins). However, it looks like they were on the right track.

The differences are more than profound

Over the centuries, regional differences in various characteristics have led to the recognition of various subforms of killer whales that are separated into “types” and “ecotypes” rather than separate species. Factors here include the animals’ body size, color, pattern, social structure, vocalization patterns, and foraging strategies.

In the North Pacific, there are three known ecotypes. The Bigg (or sometimes ‘transient’) orca, so-called resident orcas, and the offshore orca. Each has individual characteristics related to its distribution, preferred habitat and diet. For example, Bigg’s killer whales 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, while resident orcas prefer the coastal waters of the eastern Pacific and tend to eat fish, especially salmon.

Offshore orcas, on the other hand, live mainly in waters outside the continental shelf and are much 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 now, biologists have increasingly noticed key differences between Bigg’s killer whales and resident killer whales. In addition to their different diets, residents tend to move in close-knit family groups, while Bigg’s prefer to roam in smaller groups.

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

In the 1970s, Canadian scientist Michael Bigg noticed that the orcas named after him did not mix with their residential counterparts. This is typically a sign of two different species. But now researchers from the National Oceanic and Atmospheric Fisheries Administration (NOAA) and universities have confirmed Bigg’s suspicions – they are in fact two different species.

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

The results of the genetic data show that the two species likely 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 happen to occupy similar waters.

“They are the most different killer whales in the world, they live close 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 scientific panel that assessed the status of the southern residents. . “They just don’t mix.”

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

Although 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 species of killer whales. These may well include the so-called “Type D” orcas that have been seen in the Southern Ocean around Antarctica.

The article was published in Royal Society Open Science.

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