Imagine floating down from above a mountain peak as high as the Rockies and passing by rugged slopes carpeted in ancient forests that are bursting with animal life.

Now, imagine that instead of flying through the air, you're slowly sinking underwater.

That peak is a previously undiscovered extinct volcano deep in the Pacific Ocean off B.C.'s Central Coast. Instead of trees, that ancient forest is made up of red tree corals, and the animals may include numerous species that, before now, have never been seen by humans.

This surreal experience was Robert Rangeley's life for 16 days earlier this month. As science director for the non-profit Oceana Canada, Rangeley was part of a team of researchers who watched from a video feed as two remotely operated unmanned vehicles mapped and explored seamounts — active or dormant volcanoes that rise from the ocean floor — thousands of metres below the ocean's surface.

"We were just glued to the screens," Rangeley told CBC News. "We would dive from 7 in the morning to 7 at night and every turn was different."

Scientists watch a livestream of footage from remotely operated vehicles exploring seamounts off the B.C. coast. (Northeast Pacific Seamount Expedition Partners)

The mission was to explore three seamounts — the SGaan Kinghlas-Bowie off the coast of Haida Gwaii, and the Dellwood and Explorer seamounts further south.

The team also discovered six new seamounts during the expedition and collected more than 150 specimens that have been sent out for genetic analysis. Rangeley believes those specimens include new species of sponge and sea snail, and potentially some new corals.

"It was just sort of a wonderland for a biologist to see," he said.

"We saw hundreds of species — dozens and dozens of different kinds of fishes, and a range of invertebrate species, from fabulous feather stars and crinoids and cucumbers and crabs, to lobsters and octopus and so on."

A remote-operated vehicle called Hercules is deployed from the EV Nautilus for its first dive of the expedition. (Northeast Pacific Seamount Expedition Partners)

Representatives from Fisheries and Oceans Canada, the Haida Nation, Oceana Canada, and Ocean Networks Canada were all part of the expedition aboard the Ocean Exploration Trust's ship EV Nautilus.

They wanted to learn more about these unique ecosystems that begin up two kilometres underwater and are still largely unknown to science.

Just a small percentage of the world's seamounts has been mapped to date. Researchers estimate that the Pacific Ocean contains as many as 50,000 that rise 1,000 metres or more.

B.C. is a hot spot for these underwater mountains. About 87 per cent of known seamounts in Canada are located in what scientists call the "Pacific Offshore Area of Interest" — a 139,700-square kilometre patch of ocean west of Vancouver Island.

The scientists gathered more than 150 specimens from the seamounts. (Northeast Pacific Seamount Expedition Partners)

"It's really a complex habitat of pillow lavas, ripples in the rock, cliffs and everything else, and they've been all colonized ... by all these animals — corals and sponges and anemones," Rangeley said.

B.C.'s seamounts are also home to delicate metre-high vase sponges, threatened rockfish species, and bizarre deep-sea species like the longfin dragonfish, which Rangeley compares to the monsters in the Alien movies.

Prowfish like these are rarely seen and rarely photographed. (Ocean Exploration Trust, Northeast Pacific Seamount Expedition Partners )

The sheer diversity of life the researchers saw has Rangeley calling for the seamounts to be protected from bottom-contact fishing and other potentially destructive industry.

He said the team saw lost fishing gear on the slopes of the seamounts and found fishing lines tangled up on the ocean floor.

"Around the world, seamounts have been targeted for fishing because they are highly productive areas," he said.

"The fragile nature and the importance for marine life is such that we just can't be dragging fishing gear or deep-sea mining into these habitats."

During the expedition, the unmanned vehicles also installed long-term monitoring equipment on the Dellwood seamount to keep an eye on how the ecosystem changes over time.