The high seas—the vast roiling ocean that reaches beyond a coastal states’ 320-kilometer exclusive economic zone, or EEZ—is Earth’s largest biosphere. It represents about 58 percent of our planet’s oceans and is mostly unexplored, exhaustively exploited and in rapid decline. That’s why there was cause for celebration a few weeks ago when, after a decade of hair-pulling discussions, national representatives at the United Nations finally agreed that the high seas need protection.

“For the first time in history, states recommended by consensus that an international treaty be negotiated to address the urgent crisis of biodiversity loss on the high seas,” says Daniela Diz, a marine policy expert at WWF (World Wildlife Fund), who sat in on the consultations, “It’s an important step forward.”

And it’s also about time, based on the findings of the Census of Marine Life, a decadelong survey of the global oceans, which estimated that 90 percent of large predatory fishes, such as tuna, billfish and swordfish, have disappeared from the seas. Harmful fishing practices add to the threat. Bottom trawling, which accounts for most of the deep-sea fishing in the high seas, works by scraping heavy nets across the seafloor, annihilating thousands of years of growth—where vulnerable marine ecosystems such as deepwater corals and sponges, seamounts and hydrothermal vents, house slow-growing fishes like orange roughy, which live longer than humans—in an industrial minute. Much of the trawl’s catch, or bycatch, is thrown back dead.

The reason for this unrestrained use? Although not utterly lawless, high seas management is a jumble of institutions and regulations. There’s the International Maritime Organization for shipping; for mining, the International Seabed Authority; and, where they exist, Regional Fisheries Management Organizations for fishing. This fragmentation of governance has made it virtually impossible to safeguard a slice of the high seas, no matter how large or small. “The new agreement will be about what we keep in the seas, instead of what we extract,” says Karen Sack, director of The Pew Charitable Trusts’ International Marine Program, who has been involved in these discussions since the beginning in 2004. In terms of overfishing the agreement would, among other things, make it much easier to establish marine protected areas (MPAs) in international waters.

MPAs are the oceans’ national parks. They range in size and level of protection. Twelve percent of the world’s land is currently protected in national parks and wildlife preserves. In sharp contrast about 1 percent of the high seas is protected. The plan is to increase this number to 10 percent by 2020 and eventually to 30 percent, an ambitious goal considering the huge strides in international cooperation that will be necessary.

A recent report by the Global Ocean Commission (pdf), an international panel of heads of state, government ministers and business leaders, pinpoints lack of adequate governance as the crucial issue causing the demise of the high seas. It calls on countries to promptly negotiate and adopt this new agreement. According to the commission, other problems include harmful fishing subsidies, lack of tracking for fishing vessels, little accountability for offshore oil and gas exploration, and plastics pollution. Should these measures not be implemented adequately within five years, the commission suggests closing the high seas to fishing. “This proposal is not anti-fishing,” says Rémi Parmentier, commission deputy executive secretary. “There is a body of scientific evidence that if you stopped fishing in the high seas there would be dividends or benefits in terms of fishing within the EEZs.” Coastal states would benefit from the measure, he says, “A lot of them are suffering from fish being depleted by high-seas fishing fleets and distant water fleets, particularly in west Africa.”

Parmentier is referring to a piece in PLoS Biology published in March 2014. It suggested that preventing fishing in the high seas is the best way to boost the recovery of large, migratory fishes as well as increase fisheries' profits and yields.

The fear, says Matthew Gianni, co-founder of the Deep Sea Conservation Coalition, an environmental group that aims to save the high seas, is that a complete closure may incite countries to expand their EEZs (they originally extended only 20 kilometers) and regulate themselves. “There’s a lot of merit to collective regulation,” Gianni says.

And yet, the evidence in favor of closing the high seas to fishing is mounting. On February 12, a study from the University of British Columbia (U.B.C.) proposed that closing the high seas would not only have ecological and economic benefits but social advantages as well.

Researchers examined where the overlaps occur between fishes caught in the high seas and within coastal zones. They found that over 40 percent exist in both, and closing the high seas would cause an upsurge in the amount of fishes caught annually, a greater number of countries could access these fishes within their EEZs and the high seas would become the “biggest savings account on the planet.” Major fishing nations, including Japan, South Korea and Taiwan, however, would lose hundreds of millions of dollars each year.

If the implementing agreement is successfully negotiated though, there may be no need for closing down the high seas to fisheries because some key areas would be set aside for marine protection, and areas outside the MPAs would be subject to impact assessments, helping ensure this health is maintained in the long run. “I realize what we have lost,” says Enric Sala, a National Geographic Society Explorer-in-Residence and co-author of the U.B.C. paper, who dives in some of world’s least-touched waters. “I also see what the ocean of the future can be,” he adds. “It’s the difference between the places that are degraded and places that are pristine and beautiful that gives us hope.”