Legend has it that in the 1600s, one could walk across the ocean on the backs of Atlantic cod. The Gulf of Maine’s iconic groundfish was so plentiful the species spawned colonial America’s first true industry: groundfishing.

But after centuries of overfishing and failed regulation, the Gulf of Maine looks drastically different. There are few spots where Atlantic cod approach being as plentiful as they once were. One of the few is Cashes Ledge, a 530-square-mile area of ocean 100 miles southeast of Portland.

A coalition of conservation groups, supported by more than 200 marine scientists from across the U.S., are pushing for President Barack Obama to designate the area, essentially a submerged mountain range, a marine national monument. The designation would protect Cashes Ledge permanently from commercial fishing — phasing out the limited amount allowed now — and other activity that could exploit or disturb the area’s ecosystem.

The push to make Cashes Ledge a marine national monument has drawn opposition from groups representing fishermen, which point out the area is already largely off limits to commercial fishing and that the designation would circumvent the nation’s established fishery management system. It also is opposed by those, such as Gov. Paul LePage, who are wary of a potential federal designation.

Indeed, the most ecologically destructive kind of commercial fishing is already barred in Cashes Ledge, and the area has enjoyed that level of protection for more than a decade. There also is widespread agreement among fishermen, fishery managers and environmentalists on the area’s unique ecological value.

Still, the area — which has been subject to overfishing before — deserves the permanence of the marine national monument designation.

The president can apply it without congressional approval. Under the 1906 Antiquities Act, “historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest” are eligible for the designation, which would require an act of Congress to reverse.

Cashes Ledge certainly meets that admittedly vague Antiquities Act standard. It also meets the stricter definition in federal law of a Habitat Area of Particular Concern — a designation for areas of the ocean that have a particularly important ecological function, are especially sensitive to human disturbance, and are a rare habitat type worthy of scientific exploration.

Scientists who have studied it regard Cashes Ledge as an area that shows how the entire Gulf of Maine once functioned — as an ecosystem with groundfish such as the Atlantic cod as the primary predators, nutrient-rich waters because of the confluence of currents along the underwater ridge, the deepest kelp forest in the gulf and a level of biodiversity that’s largely unmatched. Since it shows how the Gulf of Maine once functioned, Cashes Ledge can show how the gulf will respond to environmental threats such as climate change.

Scientists also have found the ecosystem is particularly vulnerable to groundfishing — especially the type that relies on towing a net along the ocean floor, which can prove disruptive to the entire ecosystem. Researchers have calculated that it could take up to 268 years for some of the rarest species found in Cashes Ledge to rebound from such a disturbance.

Atlantic cod depend on that ecosystem, and if they stand a chance of recovering from their current state of near depletion, there’s a good chance Cashes Ledge will play an important part in the recovery, Robert Steneck, a University of Maine marine ecologist, said.

While fishery regulators have designated Cashes Ledge a Habitat Area of Particular Concern for these reasons, the designation provides no additional protections beyond the potentially temporary fishing restrictions already in place.

Proponents of designating Cashes Ledge a marine national monument have highlighted the designation’s ability to spare the area from energy exploration, such as oil and gas drilling. But it’s unlikely that the Gulf of Maine holds significant oil and gas deposits, and Cashes Ledge doesn’t come anywhere near proposed underwater electric transmission line routes.

Proponents’ stronger case is Cashes Ledge’s indisputable scientific value and the importance of setting it aside as a monument with scientific research as the primary purpose.

The same coalition also is pushing to designate another area, the farther-offshore Coral Canyons and Seamounts Area, as a national marine sanctuary. Those deep-sea canyons are significant — perhaps the marine equivalent of the Grand Canyon — but protecting Cashes Ledge has more practical value and should be the more urgent priority.

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The BDN Editorial Board

The Bangor Daily News editorial board members are Publisher Richard J. Warren, Editorial Page Editor Susan Young, Assistant Editorial Page Editor Matt Junker and BDN President Todd Benoit. Young has worked...