Bering Sea Canyons and Deep-Sea Corals: The Case For and Against Closing Them to Fishing

The Bering Sea off Alaska is one of the most productive ecosystems anywhere: nutrient-rich water wells up and feeds everything from crabs to whales. It also supports some of the world's most valuable fisheries, including salmon, king crab and the biggest of them all, Alaska pollock, and they last only as long as the ecosystem stays healthy.

This explainer, written by NOAA Fisheries in 2014, sets out the question then before the North Pacific Fishery Management Council: whether to close the Bering Sea canyons, or parts of them, to fishing to protect deep-water corals.

Why pollock is counted as sustainable

Pollock is the nation's largest catch and one of its most sustainable:

• nearly all the big ships that land most of it carry independent, NOAA-trained observers, who record both the catch and the bycatch of other species;
• bycatch is limited by closed areas, changes to gear, and caps that close the fishery when reached;
• a catch-share system gives fishermen a stake in protecting the stock;
• NOAA Fisheries surveys pollock at sea every year, and the North Pacific Fishery Management Council sets catch limits from those stock assessments.

That model, regional councils deciding on NOAA science, dates back almost 40 years, and Bering Sea pollock has never been overfished in that time. But new questions keep arising. One is whether fishing gear, including pollock nets, is damaging deep-water coral in the Bering Sea canyons. The Council opened a public process to decide whether and how to protect those corals; NOAA Fisheries' part is to give it independent science and advice.

Near the Aleutian Islands, 307 meters down: bubblegum corals, hydrocorals and sponges, sheltering a rougheye rockfish. NOAA Fisheries.

Corals in cold, dark water

Most people know corals from shallow, sunlit tropical reefs, where they give fish and invertebrates shelter, food and places to breed. Corals also grow in the deep, cold sea, out of the sun's reach. With no light they cannot host the photosynthetic algae of reef corals, and filter their food from the water instead. They live beyond the depth divers can reach, so little is known about where they grow, how they live, or how much fish and invertebrates depend on them.

The canyons

Several hundred miles offshore, the floor of the Bering Sea drops toward the abyss. Most of the slope falls gently, but in places canyons cut deep into the slope and shelf. They are not the V-shaped canyons of land: some are broad, gently sloping amphitheaters, others broad but steep and rugged. Pribilof Canyon is so wide that it covers about 10 percent of the whole Bering Sea continental slope.

Parts of the canyons hold deep-sea coral communities that shelter many fish and crustaceans, commercial species among them. Those habitats are easily damaged by fishing gear and slow to recover, which is why several environmental groups asked the Council to close the canyons, or parts of them, to fishing.

The questions, answered

Are the canyons unique habitat? A NOAA Fisheries study in 2012 of corals, sponges, crabs and fish found that what lives on the slope changes mainly with depth and latitude. At the same depth and latitude, the mix of species inside a canyon was much like the mix outside: dropped at random onto the slope, you could not tell from the animals around you whether you were in one.

The study did find relatively dense corals in western Pribilof Canyon, but they ran on beyond the canyon onto the neighboring slope. Dense for the slope, they appeared to reach only about one-fourth the density typical of the Aleutian Islands, and about one-twentieth that of the Aleutian coral gardens, closed to fishing in 2006.

Is closing the canyons the best protection? The canyons are huge, much of them has little or no coral, and plenty of coral grows outside them. If the aim is to protect sensitive habitat, closing the canyons as such may not be the best tool.

Why not protect only the dense patches? There was not yet enough information to find them. Submersibles had visited the seafloor only a few times, and the area is far too large to cover that way. Scientists rely instead on models that predict where corals are likely from bottom type, depth and currents, and those models were then coarse and highly uncertain: too uncertain to draw tight boundaries.

Then why not close large areas now, as a precaution? High uncertainty usually argues for caution. But NOAA Fisheries expected to cut that uncertainty sharply that summer with the first large-scale survey targeting corals in the Bering Sea, whose results would test and sharpen the models and, if dense coral exists, point to it for focused protection. The coarse models could have been used to close Pribilof Canyon and its neighboring slope, more than 10 percent of the slope, but a closure that large risks side effects: fishing pushed elsewhere could raise Chinook salmon bycatch, for example, or move the damage to other habitats.

What would the survey add? A camera lowered at 300 sites along the eastern Bering Sea slope, from roughly 150 to 1,000 meters deep, the band where most fishing, and all trawling such as pollock's, takes place, though the canyons go far deeper. No systematic, large-scale coral survey had been tried there before, and it would greatly improve knowledge of where corals and other bottom life occur, and how much of it there is.

How the Council decides

In April 2014, the Council voted to study whether and how to protect corals in and around Pribilof Canyon, chosen first because the models placed the densest corals there. That set off defined steps: gathering data, taking public comment and weighing alternatives, with the summer survey informing them.

The process is open and pauses for public comment along the way; it is the same channel environmental groups used to raise the issue. Judging by earlier closures, it would take 2 to 3 years, and the outcome could be anything from large closures to small ones to none.

The Council has a record of protecting habitat through it:

• 2006: six marine protected areas around the Aleutian Islands coral gardens;
• 2008: the Northern Bering Sea Research Area, closed to bottom trawling over an area the size of Arizona;
• 2009: all U.S. waters north of the Arctic Circle closed to commercial fishing until there is the science to fish there sustainably, even as retreating summer sea ice opens the Arctic to shipping and energy.

Each of those rested on the same kind of science and the same deliberation. The argument NOAA Fisheries made was one of timing: industrial fishing had gone on in these waters for more than 50 years, there was no emergency, and if the corals are worth protecting, the research needed to protect them in the right places is worth the time.

Sources

• NOAA Fisheries, "Canyons, Corals, and Sustainable Fishing in the Bering Sea"; rewritten in hubnx's own words. Image: NOAA Fisheries. Maps credited to Wikimedia, Esri and the North Pacific Fishery Management Council, and submersible photos co-credited to Greenpeace USA and UC Santa Barbara, are not reproduced here.