Mysterious shark-bitten orcas feeding on sperm whales don’t fit into any known category

Marine biologists are trying to understand a range of 49 killer whales whose physical characteristics are a mix of those normally associated with separate populations. Animals have been seen attacking sperm whales, a northern elephant seal and a turtle, while also bearing the marks of frequent duels with sharks. There’s a reason Orcinus killer whale have been lumped together with the popular name they have – but it seems this group is fearless even among killer whales.

“The open ocean is the largest habitat on our planet and observations of killer whales on the high seas are rare,” the new population study’s first author, University of British Columbia master’s student Josh McInnes, said in a statement. That’s why McInnes and colleagues were intrigued by reports of the whales far off the coasts of California and Oregon. That interest grew as they found more information about them.

Orcas are distinguished by the fact that different populations have very varied diets and behaviors. Some live on fish, but others target larger (but rarer) marine mammals. Off the west coast of America, some are considered ‘residents’, located in the same territory, while others are classified as ‘transients’ or ‘offshores’.

Although the population in question has been sighted since 1997, encounters with humans – at least those that have been reported – are rare. McInnes and co-authors have compiled nine reports that appear to be from the same group. These come from fishermen, whale watchers and researchers, who are between 15 and 370 kilometers (10-220 miles) offshore.

Orcas that live closer to shore are seen often enough to become very familiar. Without such reports, McInnes and coauthors had to be sure that the reports from that time were in the same population. They were surprised to find traits normally associated with different population types in one group.

“Although the sizes and shapes of the dorsal fins and saddle surfaces are similar to those of transient and offshore ecotypes, the shape of their fins varied, from pointed like transients to round like those of offshore killer whales,” says McInnes. “Their saddle spot patterns also differed: some had large uniform gray saddle spots and others had smooth, narrow saddle spots, similar to those of killer whales in tropical regions.”

A comparison of the known lifestyle of killer whales and the newly described population.

A comparison of the known lifestyle of killer whales and the newly described population.

Image credits: University of British Columbia

If such a mixed population were found among the humans, one might conclude that they were outcasts from different societies, coming together like bandits to make the badlands their own. Too much anthropomorphization can be dangerous, but observations suggest something similar.

McInnes stressed to IFLScience that this is not a new species, as some media have reported.

“During one of the first encounters researchers had with a group of these oceanic killer whales, they were observed taking on a herd of nine adult female sperm whales, ultimately making off with one. This is the first time killer whales have been reported attacking sperm whales on the West Coast,” McInnes said. “Other encounters include an attack on a pygmy sperm whale, predation on a northern elephant seal and Risso’s dolphin, and what appeared to be a post-meal break after capturing a leatherback sea turtle.”

Catching larger whales such as humpback whales can be dangerous enough for orcas, but sperm whales will likely be more difficult again. There’s a reason Moby Dick Nothing has been written about a blue whale – sperm whales are not as large as some of their baleen cousins, but they are much fiercer. It was the sperm whales who may have figured out how to fight back against the whalers and shared that information.

Nevertheless, reports indicate that it was the killer whales that had the upper fin.

“The sperm whales were in a rosette formation,” the authors write. “Small concentrated groups of four to five killer whales randomly targeted individual sperm whales in the rosette […] run in and lunge at the sperm whales or hit them from below. After each attack, fresh blood and an oil slick of animal fat could be seen on the surface. Several sperm whales had serious injuries […] One of the sperm whales was killed and dragged away from the rosette, while several killer whales fed on the carcass. The remaining sperm whales were all believed to have been seriously or fatally injured.”

On the other hand, an attack was thwarted five days later: additional sperm whales arrived to relieve a vulnerable group, and the orcas retreated.

Yet these orcas are not the only tough guys in the sea. All but three of the 49 have marks from cookie cutter shark bites. Because cookie cutters prefer tropical waters, the frequency of the bites indicates that the orcas likely spend a lot of time in the deep waters further south.

Maybe they should team up with Starboard, the orca who was recently seen eating a great white shark alone, though there’s a small matter of an ocean and a continent between them.

“We hypothesize that these killer whales may represent a distinct oceanic subpopulation of transient killer whales, or an undescribed oceanic population that feeds on marine mammals and sea turtles in the open ocean beyond the continental shelf,” McInnes and co-authors write.

Hopefully further observations will reveal more.

The study was published in the journal Aquatic Mammals.

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