There’s a narrow window when Hakai researchers are able to dive British Columbia’s Hoeya Sill, a site of rich biodiversity hidden within dynamic currents and challenging depths.
Research diver Ondine Pontier illuminates a rare red tree coral near the Hoeya Sill in the Gwa̲xdlala/Nala̲xdlala Marine Refuge in Knight Inlet, British Columbia.
Scientific diver Zach Monteith floats in the frigid black waters 40 meters below the surface of Knight Inlet, British Columbia, taking measurements of rare red tree corals. At this depth, he has only a few minutes before his time is up and he must surface and return to the boat waiting in the middle of the inlet.
To signal his surfacing location to the boat, he fills a marker buoy with air from his tank and releases it, expecting it to blast upward. But instead, as he lets go, the balloon-like marker moves sideways, pulled by the currents. This is one of the difficulties of doing scientific dives at Hoeya Sill, a raised ridge on the seafloor formed by glacial deposits halfway up Knight Inlet.
“Because you have no reference point, it feels pretty calm and normal as you ascend,” says Monteith. “And then when you shoot the surface marker and it goes sideways, you realize, Oh, I’m whipping along in the current.”
Underwater videographer Grant Callegari prepares to reboard a dive boat in Knight Inlet, burdened by his heavy dive camera as he swims against a strong current.
With limited windows for slack tide and reduced dive time due to the depth, the experienced divers have learned that it’s next to impossible to dive at this location when the tide is rushing in or out. Monteith and his fellow divers plan carefully in advance to hit the 10- to 15-minute window at slack tide for each survey. Even then, currents can be strong and the divers must adapt their dive plans to fit the local conditions. Monteith says it’s easily the most technical diving done by Hakai Institute dive teams. Local experience and knowledge of the conditions are critical.
Monteith and his highly skilled colleagues are part of a team of Hakai Institute scientists working alongside the Mamalilikulla First Nation Guardians, who are traditional stewards of the area and have extensive knowledge about these waters. The dives are part of a survey program now entering its fourth year in the Gwa̲xdlala/Nala̲xdlala Marine Refuge in Knight Inlet: more than 20 square kilometers designated in 2021 as an Indigenous Protected and Conserved Area (IPCA).
“The Mamalilikulla are extremely grateful to have formed a partnership with the Hakai divers,” says Barb Drennan, resource stewardship coordinator for Mamalilikulla First Nation. “Without them, we would not have valuable information about the sill.”
The underwater surveys are part of a multifaceted approach to studying and monitoring the inlet. They include bathymetric surveys and the collection of environmental DNA (eDNA) samples in the water. Dive surveys are well suited to recording conspicuous invertebrates like sea stars and corals; eDNA is effective at capturing a snapshot of the local biodiversity, from fish to algae and marine fungi.
By identifying the rare shallow occurrence of gorgonian corals like the red tree coral, and shedding light on the biodiversity that thrives in these deep inlets—home to basket stars, glass sponges, and endangered sunflower sea stars—the project partners hope to detect changes in these underwater ecosystems and prevent the unintentional destruction that can occur without the protections of IPCA status.
The dive team has observed monofilament fishing line entangled in red tree coral on numerous occasions, as seen on the right-hand coral in this photo. Sometimes fishing line breaks off the delicate branches of the coral.
On the request of the Mamalilikulla First Nation’s stewardship team, the divers have been keeping their eyes open for signs of human impacts on the corals. The dive team has observed fishing lines tangled in the intricate coral branches on several occasions. “There was a fan that I found that was knocked over on the sill, lying down and in the process of dying,” says Monteith.
Upon further inspection, they discovered there was monofilament line tangled around in it. The team suspects that came from a trolling fisherman and got wrapped in the coral, pulling it over and breaking the line.
Red tree corals grow less than two centimeters each year, so finding a coral fan the size of a hula hoop means the organism could be well over 100 years old. To explore ways of quantifying the growth rate of red tree coral, the research team is experimenting with techniques like photogrammetry, a method of creating a three-dimensional model from a series of photos.
Red tree coral can be found at the upper extent of their preferred depth, where currents whirl over the Hoeya Sill. The sill restricts water entering the inlet and results in strong currents that surge over it—creating a high-nutrient shallow environment that teems with life.
But finding the pinnacles—the coral hotspots—and staying on them is a challenge unto itself. The inlet ranges from 300 to 700 meters deep, and landing on a pinnacle without the help of instrumentation and data would be like playing a blind game of Battleship.
The old Mamalilikulla village site and float house can be seen on Village Island with Knight Inlet extending beyond.
Fortunately, thanks to multibeam surveys, researchers can map out the seafloor ahead of time and target the pinnacles and boulders that might be good habitat for red tree coral.
Ondine Pontier, a fellow Hakai Institute research diver on the project, describes the satisfaction of nailing the slack tide and seeing the habitat in all its glory.
“You’ll be down there and all of a sudden all the fish just come out when it’s slack,” she says. “So you’re lighting up this scene of pink, orange, and gold like you’re in a dragon’s lair.”
In October 2024, Hakai research divers found a nudibranch on Hoeya Sill that they believe has never been described before.
The team also benefits from deploying an ROV, or remotely operated vehicle, which Hakai Institute hydrographer Nick Viner uses to film the seafloor and scout proposed dive sites.
The divers refine their strategy for surveying with each passing season, learning from the conditions as they go. Luckily it’s a team effort.
“You have your dive tender who’s helping you do all those checks beforehand and getting you into that mental space … and helping with the dive tables,” says Pontier. “It’s great to have a team that you really trust in the end.”
Underwater videographer Grant Callegari has been diving with the team for two years and has the additional task of making sure all his camera gear is arranged perfectly for each dive. With all the work that goes into these dive trips, it can sometimes be hard to tear himself away from that perfect shot while they’re underwater, he says.
“I remember the last dive of my first trip, going down and just at the very end of that intense dive on the sill, I swam a little bit farther on from where we usually go and I found this motherload of giant corals,” says Callegari. “But I’d run out of time, so we had to go back up and wait a whole other year before we were able to dive at that exact same spot.”
