UBC researchers find little-known type of killer whale that preys on large sea mammals

A group of University of British Columbia researchers, set on uncovering the mysteries of the deep, have discovered a little-known type of transient orca that preys on grey whale calves and other large sea mammals.

After analyzing over 100,000 photographs taken off the Canadian and U.S. west coasts, scientists encountered a group of "outer coast transient whales," who rarely travel to the coast.

"These whales prefer deep water. So they were found offshore near canyon systems, which are very productive areas where there is a lot of nutrient upwelling, and it attracts other marine life," said Josh McInnes, a marine mammal researcher at UBC who led the study.

Of the 155 encounters from 2006 to 2019, most of the whales were found in the offshore waters between Oregon and central California, but 26 were spotted off of Vancouver Island.

McInnes says the outer coast whales are thought to be a subset of mammal-eating transients, also known as Bigg's killer whales. Before the study, coastal and outer-coast transients were assumed to belong to a single population.

He says the difference between the two goes beyond just habitat. 

"We see a seasonal trend where they show up in the spring and they follow the grey whale calves that are migrating up from Baja," McInnes told CBC.

He says they will target the whales as prey along with elephant seals and oceanic dolphins, where Bigg's transients prefer smaller mammals like harbour seals and porpoises. 

Whales exhibit unique dialect

The study revealed that when encountered outside of California waters, the outer coast whales have been observed associating with other known coastal transient groups but exhibit a unique vocal dialect, distinct from other transient dialects in the coastal waters along the Pacific Northwest.

McInnes says the study, which was a collaboration between UBC and the National Oceanic and Atmospheric Administration (NOAA), also made another astonishing discovery.

He says that far past the continental shelf in the open waters of the Pacific, they found an unknown group of killer whales who were eating sharks.

"We have no idea who they are," McInnes said. "They looked like transients. There was some similarities to them as well. Some of them had what we call cookie-cutter bite marks, which are these circular scars on the body of the animal."

He says these were caused by parasitic sharks that live far offshore, giving researchers an idea of where the killer whales might be spending their time. 

McInnes says this is only the first chapter of the work his team is trying to conduct. 

"For me, this is big because there's been a lot of information missing for some of these animals," he said. 

The next step will be to continue the research into new avenues of comparisons between different communities of whales in B.C. and compare the diets and behaviours, McInnes says.