(CNN)Swimming deep in the Pacific Ocean, a group of little-known killer whales that eat large sea mammals including grey whale calves has been found, researchers say.
In a recently-published catalog, researchers from the University of British Columbia examined 13 years of photo-identification data and more than 100,000 photographs taken off North America's west coasts. What they encountered was a group of what they referred to as "outer coast" transient whales, which rarely traveled to California's coast and hunt massive elephant seals or sea lions.
"What we did with this catalog is report 150 killer whales that seem to be different from other groups of killer whales," said Andrew Trites, director of the Marine Mammal Research Unit at the University of British Columbia, who co-authored the study.
According to Trites, there are different types of killer whales in the Pacific: residents, which eat fish; offshores, which consume sharks; and transients, which specialize in eating marine mammals. Trites noted how it has been known there are two populations of resident killer whales, northern and southern, which have been extensively studied since they live very close to shore.
"We've got some evidence suggesting that the transient population should be considered as two distinct populations, and the one that we're seeing most frequently in California, we suspect they may specialize in eating small whales and elephant seals," said Trites.
Trites told CNN around Monterey Bay, the continental shelf -- the edge of a continent which lies under the ocean -- comes in very close to land, which is where the population of "coastal" whales has been primarily seen. Yet the researchers encountered a group of mammal-eating "outer coast" whales that rarely travel to the coast, preferring deeper water and living offshore near canyon systems.
Of the 155 encounters from 2006 to 2019, most of the whales were found in offshore waters between Oregon and central California, though 26 were spotted near Vancouver Island. Outer coast whales also exhibit a way of communicating with each other outside of California waters, distinct from other transient whales in coastal waters of the Pacific Northwest.
"In the same way that when the distinction [was] made between Northern and Southern Resident killer whales, that shaped the understanding of their needs in terms of conservation or threats they faced," Trites said. "If indeed there are two distinct related populations of transient killer whales, they presently have different needs as well."
A "significant contribution" to killer whale research
Brad Hanson, a wildlife biologist with NOAA's Northwest Fisheries Science Center who has researched Southern Resident killer whales, commented many of the whales had not previously been matched to existing photo ID catalogs until the new findings. Now, with many more individual whales cataloged, researchers can start to understand more about their ecology.
"[This research] is a significant contribution in my mind because these photo ID catalogs are essentially the foundation of virtually all the work that we do on killer whales," Hanson told CNN.
Jenny Atkinson, executive director of The Whale Museum in Friday Harbor, Washington, told CNN there have been conversations over whether fish-eating and marine mammal-eating populations are different species, because right now, they are all classified as just killer whales.
"We didn't really see transients before, we didn't see them in these numbers," said Atkinson. "We didn't know how they were associated. We always thought it was this rogue group of killer whales that got together for successful hunting strategies, and they traveled up and down the coast looking for marine mammals to predate on. But the more encounters you have, the more you can add a data point or information to your long-term research."
In 2010, according to Atkinson, researchers used to say transients come in groups of three or four and were not necessarily associated. By 2011, though, they started seeing groups of 20 to 25 that come into the waters, and now transients come back year after year as a family group with their offspring.
Although Atkinson is not a researcher, she told CNN as far back as 10 years ago, transients were recorded coming into inland waters and predating on adult gray whales right in front of whale-watching boats. She believes the new catalog will be helpful in furthering research on diverse transient whale behaviors.
"They're starting to suss out associations and relationships and starting to look at whether or not these different, for lack of a better term we'll call it sub-pods or groups, are associating as an acoustic plan or developing hunting strategies," she said. "What's cool is that they've looked at all this different data, they're trying to make sense of it in a way that we've not been able to do before."
Unknown group of killer whales also found
The catalog also pointed to another astonishing discovery: an unknown group of killer whales that resembled transients but eat sharks like offshores.
Trites said a few whales were found washed up on shore dead which were not previously known, and their teeth were ground down almost to the gum line. This suggested there must have been something very abrasive that ground down their teeth.
"And what's more abrasive than the skin of a shark?" Trites asked.
The whales looked like transients and had cookie-cutter bite marks, or circular scars on the body of the whale. These may have been caused by parasitic sharks living offshore, which may point to where the killer whales spend their time.
The next step, according to Trites, is to continue updating the catalog, since there are still many more types of whales to be discovered. In addition to increased efforts for sightings and acoustics research, scientists will continue to find out more about transients and better understand how killer whales establish themselves as the top predators of the oceans.