A rare subspecies of killer whales, also known as orcas, is seen Monday in Kachemak Bay. -Photo by Craig Matkin

A rare subspecies of killer whales, also known as orcas, that prey on sharks was seen on Monday in Kachemak Bay. Dave Lyon of Ashore Water Taxi

first reported the pod of about 25 whales, and

researchers with the North Gulf Oceanic Society investigated.

Whale biologist Craig Matkin said that based on the shape of the whales’ dorsal fins and their behavior he thinks they are offshore killer whales, a subspecies that migrate between California and Alaska. Other subspecies include resident killer whales that feed on salmon and transient killer whales that feed on marine mammals.

“I get out there and expect them to be residents or transients, and I get out there and I go, ‘what the hell, these don’t look familiar,’” Matkin said.

“I’ve never seen them in here. … It was really cool, a big surprise.”

This was the first documented sighting of offshore killer whales in the bay, and the earliest arrival of offshores in Alaska for the season, he said.

About 13 to 15 feet long, offshores feed on the fat-rich livers of sharks. They swim erratically and dive deep to hunt sharks. Matkin collected liver samples from scraps bobbing on the surface and said he believes the sharks hunted were Pacific sleeper sharks. Genetic testing will prove that.