Schools of rockfish play among coral forests. Brittle stars cling to massive trumpet-shaped sponges. Octopi and crabs are tucked into every crevice. It’s a scene you’d expect to see on a tropical reef, not hundreds of kilometres from shore, in the lightless depths of the open ocean.

But it’s exactly what a team of scientists discovered when they set out to map an extensive undersea mountain range off the coast of British Columbia earlier this month. Now, Oceana Canada says their findings support a case for protecting these seamounts from bottom contact fishing and other potentially destructive activities.

“The biodiversity within those corals and the amount of productivity [on the seamounts] was phenomenal,” says Robert Rangeley, Science Director of Oceana Canada, which was a partner in the expedition along with Fisheries and Oceans Canada, the Haida Nation, and Ocean Networks Canada. “These are important refuges for healthy oceans, and they should be permanently protected.”

Expedition members spent 16 days aboard the Ocean Exploration Trust’s EV Nautilus, mapping and exploring a chain of underwater extinct volcanoes as high as the Rocky Mountains, thrust up from the seafloor more than 100,000 years ago by the same massive tectonic forces that continue to shape the Pacific Northwest today. Every day brought new surprises, from previously unidentified species of sponges to unbelievably complex and interdependent colonies of corals, anemones, snails, crabs and fish.

“You’d think if you dove into the deep sea, you’d see the abyssal plain — mud and not much else,” says Cherisse du Preez, a marine biologist with Fisheries and Oceans Canada. “As a seasoned scientist, I didn’t know that the deep sea could be so plentiful, so rich.”

But the team also found discarded fishing gear in parts of the range that were previously open to bottom contact fishing, including within the SGaan Kinghlas-Bowie Seamount Marine Protected Area off the coast of Haida Gwaii. The Bowie Seamount and two neighbouring seamounts have been federally protected since 2008, but were only closed to bottom contact fishing earlier this year at the request of the Haida Nation.

“We were finding the gear wrapped up in the corals, wrapped up in the sponges, and the animals they were entangled with were not in good condition,” says du Preez. “It’s hard to see a thousand-year-old coral that’s being choked out.”

Seamounts are often targeted by bottom trawlers precisely because they attract a wide variety of marine life. Outside of Canadian waters, seamounts in the same chain have been depleted by extensive fishing. There are also fears that seamounts could be targeted for deep-sea mining or oil and gas exploration as technology evolves.

In 2017, Fisheries and Oceans Canada identified a 140,000-square-kilometre area off the coast of Vancouver Island containing 13 seamounts as a candidate for a new marine protected area. The expedition team says their findings demonstrate why the MPA is needed.

“It’s not an empty place; it’s rich, abundant, with this diversity of life playing out, and we as Canadians can actually do something about it because it’s in our waters,” says du Preez. “We’re looked upon as a leader in marine science, and I think if we step forward and are progressive with our thought, it will go a long way toward setting an example for other countries to follow.”