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Fishing and climate change threaten the open ocean. The high seas treaty could help.

What’s the largest habitat on Earth?

It’s not the Amazon rainforest or the African savanna. It’s not even the Great Barrier Reef.

It’s the high seas — a.k.a. the open ocean.

The high seas start 200 nautical miles offshore (about 230 miles), beyond any country’s national jurisdiction. This region is truly massive. The high seas cover nearly half of the planet’s surface, make up about two-thirds of the entire ocean, and represent an estimated 95 percent of all occupied habitat on Earth. 95 percent! All of the world’s forests and grasslands and lakes and rivers make up just a tiny fraction of Earth’s space for wildlife.

This gargantuan ocean habitat isn’t just some big, empty pool. It’s full of life — of whales and octopuses, albatrosses and turtles, and schools of fish that end up in restaurants and grocery stores. Plus, the high seas are teeming with microscopic critters called phytoplankton, which supply about half of the oxygen we breathe. The Amazon isn’t the lungs of the Earth. The high seas are.

A school of yellowfin tuna in the Mediterranean Sea.
Giordano Cipriani/Getty Images

Nonetheless, the high seas are nearly entirely undefended. Protected areas cover only about 1 percent of the open ocean, leaving this habitat vulnerable to overexploitation, plastic pollution, and commercial shipping — all of which harm wildlife and threaten to upend entire ecosystems on which many of us depend.

But big changes are coming, and they could help shield the high seas from many of these threats. In early March, after nearly 20 years of planning and heated negotiations, more than 190 countries agreed on a global treaty to conserve the high seas. It’s a big deal: The treaty marks the first time in history that the world has a cohesive strategy to sustain this enormous, life-supporting region.

The centerpiece of this groundbreaking treaty is a plan to establish new protected areas. These are basically big parks in the open ocean — like Yellowstone or Yosemite, but out at sea — that prohibit certain human activities that harm ecosystems and their inhabitants. As countries create more and more of them, these protected areas will count toward a big target, known as 30 by 30, to conserve at least 30 percent of all land and water by 2030. (Today, 3 to 8 percent of the ocean is protected.)

A key question now is what these protected areas will actually look like, and whether they’ll work. In some ways, parks make less sense in the open ocean than they do on land. Sharks and whales and other marine animals are highly mobile; to them, park borders are meaningless. Climate change, meanwhile, is shifting the distribution of all kinds of ocean creatures, potentially undermining the value of any protected area that’s stuck in place.

The open ocean is far from empty

From the bow of a ship, much of the open ocean looks the same. It’s blue. There are often waves. It’s overwhelmingly vast. It looks like … the ocean. But dip below the surface and a whole other world appears. Underwater in the high seas, no two locations are the same, though many of them are spectacular.

Consider a region about 1,500 miles east of Miami, in the middle of the Atlantic Ocean. Known as the Lost City, it’s a field of hydrothermal vents — towers formed around what are essentially hot springs in the seafloor that expel mineral-rich water. Some of the structures are nearly 200 feet tall, stretching as high as a 15-story building.

“It looks like an underwater metropolis,” said Nichola Clark, a high seas expert at the Pew Charitable Trusts who was involved in the treaty negotiations.

The top of a 200-foot-tall vent in the Lost City.
Courtesy of Deborah Kelley/University of Washington

Hydrothermal vents like these may hold secrets to how life on Earth began. They also support a wide array of life forms today. There are microorganisms that can turn chemicals released by the vents into energy but also larger creatures like crabs, shrimp, and octopuses, many of which are unique to this region. Remarkably, more than half of the species here may live nowhere else on Earth.

More than 1,000 miles west of the Lost City is another extraordinary site called the Sargasso Sea. It’s the only sea on Earth that has no land borders; the sea is bounded instead by ocean currents, which form a soft barrier between the sea and the rest of the ocean.

The Sargasso Sea is calm and clear and blanketed by thick, green mats of Sargassum seaweed that provide shelter to frogfish, seahorses, and other marine animals. The sea is also the only known place on Earth where American and European eels spawn (until recently, the origin of eels has been something of a scientific mystery).

The high seas have many incredible spots like these, and together they’re home to millions of species — many of which are still unknown to science. They also sustain the increasing number of people who eat seafood, such as yellowfin and skipjack tuna. While a small percentage of the fish we eat are caught in the open ocean (most of which is destined for wealthy nations), ecosystems in these regions support fisheries near shore, too.

A man fishes on Aldabra Island in the Seychelles.
Majority World/Universal Images Group via Getty Images

“Our ocean is connected,” said Sheena Talma, a marine biologist in the Seychelles who was also involved in the treaty negotiations. The Seychelles and many other island nations rely on tuna in coastal waters, Talma said, which often travel in and out of one country’s national jurisdiction (also known as its exclusive economic zone, or EEZ). “A lot of things that happen on the high seas will affect our EEZ,” Talma said.

But while island nations and many scientists have long recognized the importance of the high seas, this region has largely been overlooked by global conservation efforts. Fewer than a dozen marine parks dot the open ocean, covering just a tiny fraction of its habitat. Plus, some of them provide little in the way of protection, Clark said. And while there are many existing organizations involved in governing different activities in the high seas, including seabed mining and fishing, they don’t work coherently. Existing governance is “a hot mess,” said Sara Maxwell, an associate professor of marine science at the University of Washington.

How to protect the high seas

Without protection, the high seas have sustained damage. A 2010 study examined 48 different fish stocks in the high seas and found that two-thirds of them were “depleted or being overfished.” A more recent assessment indicates that fishing companies have overexploited more than a third of the ocean’s fish stocks (though it does not distinguish between fisheries in the high seas and those within national jurisdictions).

A Chinese fishing vessel near the Galapagos Islands on July 19, 2021.
Joshua Goodman/AP

Commercial shipping is a problem, too. As vessels carrying our TVs, cookware, and other goods travel through the high seas, they inadvertently kill whales and other marine animals, including the world’s largest fish.

Indirect threats, such as climate change, only make these problems worse. Rising temperatures are causing some marine animals to shrink, which can disrupt ecosystems that have been carefully calibrated over thousands of years. Carbon dioxide emitted by our power plants and cars, meanwhile, is making the sea more acidic, putting corals and shell-building creatures at risk.

Marine protected areas (MPAs) are one solution. Research shows that protected areas in the ocean tend to benefit resident fish and other animals if they restrict all or most destructive activities, such as bottom trawling. And that’s where the new treaty comes in: It provides a way for countries to create new marine parks in the high seas that will be recognized under one international organization.

The wing of a plane over protected ocean.

A view from above of Hawaii’s Papahānaumokuākea Marine National Monument, one of the world’s largest marine protected areas.
Saul Loeb/AFP via Getty Images

How do you put a park in the open ocean? It’s a little different from creating one on land. Forests, wetlands, and other terrestrial ecosystems often have somewhat clear borders, hemmed in by highways and other human developments. The open ocean, however, is fluid (literally) and unbounded. Many of its inhabitants are also long-distance travelers like whales and sharks.

“It is a little bit wonky that we’re trying to apply something that works really well on land in the ocean,” Maxwell said of marine parks. “The habitat is fluid, the animals are fluid, and the users — including humans in a boat — are fluid.”

But the idea of parks in the open ocean makes more sense when you consider, again, those unique underwater features. The high seas are full of submerged canyons, valleys and hills, and different currents and temperatures. These features create somewhat discrete ecosystems with assemblages of marine animals, not unlike what you find on land. While parks in the US protect, say, the Rocky Mountains, there are also mountain ranges underwater, such as the Salas y Gómez and Nazca ridges off the west coast of South America.

“How cool is that?” Clark said of these ridges. “It’s an underwater mountain range, and the diversity of life there is overwhelming.”

It’s these kinds of unique spots with identifiable features that the new treaty seeks to conserve. Marine scientists have actually already pinpointed several potential locations for protection, including the Salas y Gómez and Nazca ridges as well as the Lost City and the Sargasso Sea. These lists take into account things like the diversity of species in the area and how unique they are.

A striped marlin chases a school of sardines off the coast of Mexico.
Bernard Radvaner/Getty Images

There are still some questions about how well these parks will work. MPAs are only as effective as the rules that govern them and how well those rules are enforced. While MPAs are by definition protected, many of them — including a number of those in the US — allow for destructive activities, like commercial fishing, said Kristina Gjerde, an expert in marine law who was also involved in the treaty negotiations.

“We call the US marine protected areas ‘sanctuaries,’ and yet the only thing that’s actually prohibited is maybe oil and gas [drilling],” Gjerde said. “There’s still bottom trawling; there’s still pollution coming in from coastal regions.”

Climate change creates other challenges. Rising temperatures are reshaping the range of species and, in some cases, pushing them towards the poles, where it’s colder. Ocean plants and animals have, for example, moved poleward by an average of about 59 kilometers (37 miles) per decade, according to a 2022 report by the Intergovernmental Panel on Climate Change, making static park boundaries less relevant.

That’s one reason some scientists have floated the idea of “mobile MPAs” — essentially, parks with flexible boundaries that can move along with the shifting range of species. This concept is largely untested but doable, said Maxwell, who co-authored a 2020 study (linked above) that advocates for this approach. “It’s a really promising way to keep up with animals,” she said.

We know how to protect the planet

The treaty itself is mostly final, but it will likely be a few years before new parks in the high seas are established, according to experts. The UN has yet to formally adopt the agreement — that could happen in June, Clark said — at which point nations will have to ratify it through their own governments.

Once 60 nations ratify the treaty, known as the Biodiversity Beyond National Jurisdiction treaty, or BBNJ, the agreement will enter into force. (It’s not clear whether the US will sign on. Ratification requires a two-thirds majority vote in the Senate, and conservative lawmakers infamously do not like signing on to global treaties. Some US senators apparently do not even know what the High Seas Treaty is.)

But even then, conserving the high seas won’t be smooth sailing.

“The implementation part of the framework still needs an awful lot of work,” said Lance Morgan, president of the nonprofit Marine Conservation Institute, who also helped negotiate the treaty. “There are a lot of pitfalls potentially.”

A laysan albatross, one of the many seabirds that depend on the high seas.
Kevin Schafer/Getty Images

Leatherback sea turtles on a beach in Trinidad.
Martino Motti/Education Images/Universal Images Group via Getty Images

The process for designating new parks in the high seas is meant to be inclusive, allowing a wide range of groups — including those who advocate for fisheries — to weigh in on how these areas are managed, Morgan said. That process could ultimately weaken the regulations governing them. There’s also still a lack of data showing the range of marine species and how climate change will affect them. In short: All of the existing issues with MPAs could also affect parks in the high seas.

Still, many environmental advocates are hopeful — more hopeful than they’ve been in years. The treaty is just one tool the world now has to protect nature. Just a few months ago, nearly every country signed on to a historic plan to safeguard wildlife and ecosystems globally by, among other things, conserving at least 30 percent of the planet. “We have all of the tools we need,” Clark said. Now it just comes down to whether the world will use them.

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