A team exploring Canada's largest underwater volcano had a close encounter with a two-metre-long salmon shark about 250 kilometres off Vancouver Island.

The sighting happened July 19 while scientists were deploying equipment in the water near the volcano.

For about an hour, the team watched in awe as the shark leapt out of the water and heaved its body against a floating log.

"It was absolutely incredible," said Cherisse Du Preez, a deep-sea marine biologist with Fisheries and Oceans Canada.

"It slid along kind of like you'd expect a skateboarder to on a rail."

Get a rare, up-close glimpse of the shark:

A team exploring Canada's largest underwater volcano came across a two-metre salmon shark about 250 kilometres off Vancouver Island. 0:40

The adventure started when the team spotted a log in the middle of the ocean.

The crew — made up of Fisheries and Oceans Canada, the Canadian Coast Guard and at least one member of the Tseshaht Nation — grabbed a rope and pulled the log away, concerned it would interfere with their equipment, Du Preez said.

In the process, they dislodged some barnacles off the log, which drifted in the water.

That's when a coast guard member shouted, "Fin."

'We were in its world'

A salmon shark jumped out of the water and started scratching itself against the log, a pattern it repeated for about an hour, Du Preez said.

While that unfolded, crew members placed a GoPro on a pole and started filming underwater, she said. A crew in a nearby coast guard ship dispatched a drone.

When later reviewing the footage, the team realized the shark had large parasites attached to its fins.

The parasites live off the shark's blood and sap their energy, and the shark had tried to scratch them off, Du Preez said.

"It's the behaviour that's so shocking and unexpected," she said.

Salmon sharks, which are common off the B.C. coast, can grow up to three metres in length. They're considered potentially dangerous to humans, but have never been identified in a shark attack.

Du Preez said it was even more unusual to spot the shark in the middle of the ocean, during its yearly migration between Japan and Canada.

Josh Watts, a marine biology student at the University of Victoria and a member of the Tseshaht First Nation, was also on board. He said the shark's "artistic display" was a powerful moment.

"Even now still, when I reflect, I get emotional about it," Watts said.

"We were in its world at that time. Even just to get a glimpse of that is incredible."