Protecting the High Seas to Safeguard Migratory Marine Species

Every day, as planes carry passengers high in the sky, seabirds soar across the waves. While trains crisscross on terrestrial tracks, eels swim their way to and from a saltwater station. And as cars around the world complete their four-wheeled commutes, whales navigate superhighways to feed and breed. These creatures are just some of the many marine organisms designated as migratory species — animals whose lives revolve around traveling great distances to locate prey, give birth, and engage in different kinds of essential behaviors.

Oceanic organisms like sea turtles and sharks are true global citizens, advancing far beyond national waters and extending their range into the international waters known as the high seas. As species migrate across ocean basins, they unknowingly cross the borders of established Marine Protected Areas, the vast majority of which are designated within 200 nautical miles of shores, also known as Exclusive Economic Zones or EEZs.

The world’s first official MPAs originated in the mid-20th century, inspired at the time by a new wave of action, including the documentaries of Jacques Cousteau, the writings of Rachel Carson, and an official recommendation to create “marine parks or reserves” at the First World Conference on National Parks in 1962. Fast forward to today — when just over one-fifth of migratory marine species are considered threatened — and there exist “nearly 1,000 MPAs within U.S. coastal, oceanic, and Great Lakes waters,” according to the National Oceanic and Atmospheric Administration.

Currently, less than 2 percent of the high seas are protected as MPAs, but the United Nations 2023 Biodiversity Beyond National Jurisdiction agreement (also known as the High Seas Treaty) would allow countries to jointly establish MPAs in these international waters beyond any nation’s EEZs. The High Seas Treaty is aimed at safeguarding species from unregulated threats and giving migratory animals the chance to not only survive but to thrive.

At their most effective, MPAs increase the biomass of fish, maintain a balance between predators and prey, and allow ecosystems to develop resilience in the face of a warming planet. Created as a conservation method, they serve as key refuges for species in a world otherwise dominated by human development. Further maintained as a location of livelihood, they secure better food and higher income for coastal communities, benefiting those who live nearby.

High seas MPAs offer an opportunity to practice the art and science of marine conservation. “I think it will be really fascinating to learn and study more about how high seas marine protected areas may differ from those that are found within EEZs, in part because, of course, these places are so, so far away, and we can expect that they’re going to tend to be larger,” said Nichola Clark, senior officer at The Pew Charitable Trusts.

Following Along from Afar
For most of human history, the movements of underwater organisms remained a mystery. Out of sight for a major portion of their lives, these species have compelled scientists to follow them far offshore for research purposes, which costs both money and time. But with modern tracking technologies, researchers can dial in to the remote marine hubs where animals congregate to feed and breed.

“Animal tracking methods have been incredibly useful to quantify just how many species spend most of their year on the high seas or use the high seas as a migratory corridor,” said Dr. Autumn-Lynn Harrison, a research ecologist at the Smithsonian National Zoo and Conservation Biology Institute’s Migratory Bird Center. “Putting numbers on this and mapping important areas has been critical to the process. Today, we have longer time-series of data and more detailed observations than ever before.”

We now know that, as part of their life cycles, European and American eels traverse thousands of transatlantic miles from rivers and streams in their respective countries to spawn in the seaweed-rich waters of the Sargasso Sea. Off the coast of South America, leatherback sea turtles and waved albatrosses move through the Salas y Gómez and Nazca ridges. In the Gulf of Guinea, humpback whales and yellowfin tuna meet up with productive oceanic currents west of Africa. Some organizations have showcased these and other selected sites across the global ocean as promising candidates for protection.

“If you really want to effectively protect these highly migratory species, you need to be able to protect them at all of the important places where they spend their lives, and we know that includes high seas areas, as well,” said Clark.

Historically, the act of tracking marine animals has helped inform the establishment of protected areas. In one study, scientists analyzed over 260,000 days of animal tracking data to pinpoint the locations of 14 marine predator species throughout the Pacific Ocean. As a result, they discovered that 797 individual organisms, from blue sharks to blue whales, paid a visit to the high seas between the years 2000 to 2009. Some species, like the Laysan Albatross (near threatened), spend 75 percent of their year over the high seas.

In fact, Harrison — the paper’s lead author — presented the research at the UN’s first High Seas Treaty negotiations session in 2018. “It was incredibly fulfilling to know that I had produced science that would be used directly by global policy-makers,” she said. “This was always my goal in becoming a marine conservation biologist.”
Some migratory marine species even reap additional benefits on the high seas, according to Dr. Dan Costa, distinguished professor of ecology and evolutionary biology at University of California, Santa Cruz. He cited the example of loggerhead sea turtles that breed on the beaches of Japan and migrate across the ocean to feed off Baja California — it is these turtles that do better than their counterparts that remain in the Central Pacific, to some extent.

“The ones that go all the way over to Baja do much better because the California Current is a rich and highly productive environment,” he said. “The interesting thing is that the loggerheads that go off Baja grow faster than the ones that are staying in the Central Pacific, but the ones that go off Baja are often taken. It’s a higher probability of being harvested in an artisanal fishery.”

Monitoring for Impacts
From maps that enable MPA managers to track when migratory species overlap with fishing activities to advanced drones that can monitor animals moving around ships, the possibilities for connecting real-time data to real-world outcomes are as limitless as the ocean itself.

“If you look at a textbook in the 1990s, it showed elephant seals are just along the coast of California. With satellite tags on, we found out they use the whole northeastern Pacific,” said Costa. “We only knew where elephant seals were because that’s where we looked for them, so one of the advantages of tagging animals is that it allows us to follow them where they go, and we don’t have to go to the places where they are.”

Some argue that the most effective high seas MPAs will be those that account for human impacts — pollution, overfishing, and other development. For example, over 200 species are known to succumb to the harms of plastics — either through entanglement or ingestion — while hundreds of thousands of animals are fatally wounded each year when caught as bycatch in fishing gear.

“MPAs have been scientifically shown as an area-based management tool to help reverse population declines and maintain thriving ecosystems,” said Harrison. “For migratory species, connected networks of MPAs confer greater benefit than isolated areas, helping to maintain connectivity across their breeding, foraging, and migratory corridors.”

But it’s also important to recognize that based upon how species interact with the environment, some threats are more impactful than others. “For some species, like the big whales, which don’t feed on the breeding grounds, you don’t really have to worry about what’s happening with the prey resource,” said Costa. “Anything that might compromise their feeding behavior really isn’t an issue, but things that might compromise their breeding behavior do become an issue.”

Of course, the effects of global warming pose additional risks. In a changing climate, seabirds and marine mammals find less food as fish turn up smaller and krill become less abundant; meanwhile, sharks may shift their ranges towards the poles in search of preferred habitat. In response, some argue that mobile high seas MPAs with shifting boundaries based on species detection or sea surface temperatures could allow animals’ whereabouts to determine the most significant habitat at any given time.

Although high seas MPAs comprise just 1.4 percent of the area of the 100 largest MPAs across the globe, two-thirds of them are fully and highly protected, rendering them a significant piece of both the marine conservation — and human livelihood — puzzles.

“Yes, they are far from home, but they are inextricably connected to the shores that we are familiar with,” said Clark. “They are critical habitats for whales and seabirds and sharks and turtles and all of these other charismatic species that people are really interested in, and, of course, critical for general ocean functioning and for our habitat. They’re an incredibly important part of what makes our planet livable.”

The notion of drawing attention to international waters is, in fact, not new. In 2005, it was famed oceanographer Sylvia Earle who wrote that they demonstrate the ocean’s value to “human health, to economies, to security, to the existence of life itself.”

Twenty years later, anything can happen on the high seas.