Not far off the islands of the Republic of Vanuatu, a deserted trawl-fishing net undulates in the azure tropical Pacific. No one knows whom it belonged to or how it was lost, but it has twisted around a delicate garden of coral and damaged the reef.

It is just one example among at least 640,000 metric tons of fishing gear that goes missing at sea each year, according to the United Nations. Known as "ghost gear," it gums up ship propellers, entangles passing whales and settles atop sensitive habitats. A recent study estimates it accounts for nearly half of the large debris in the Great Pacific Garbage Patch. Because most is made of plastic, it does not biodegrade but instead breaks down into tiny particles that can enter the food chain and potentially harm animals and ecosystems.

Much of the research and cleanup efforts involving plastic ocean debris have focused on the bottles and bags that come from sources on land. But growing evidence ghost gear is also a major concern has catalyzed work to understand how best to clean it up, recycle it and (most importantly) keep it out of the water in the first place. “I went from feeling like this is such a niche topic and wondering how we were going to make any progress to now, [when] every day the phone is ringing with people who want to collaborate," says Christina Dixon, the global campaign manager for the Global Ghost Gear Initiative (GGGI) of World Animal Protection, a nonprofit animal welfare organization.

Ghost gear is so ubiquitous it affects many of those who work at sea, from merchant shippers to ocean-floor mappers. Seismic survey teams (who image the seafloor subsurface for oil and gas exploration) often find themselves acting as ad hoc cleanup crews, says Gail Adams, spokesperson for the International Association of Geophysical Contractors, an industry group for companies that run ocean-floor surveys. The organization has set up a database to track the nets its members pull from the water in the course of doing business.

But cleaning up after the fact is far from an ideal solution. Take that trawl net entangled near Vanuatu, which the GGGI and the Vanuatu Fisheries Department aim to remove by March 2019: These nets can be the width of a football field, which makes removing them from the reef a huge undertaking, says Ingrid Giskes, global head of the GGGI’s Sea Change campaign. “We will probably have to cut the net in segments, bring them up with lift bags and then winch them onto a large enough vessel," she says, adding this process requires specialist divers trained to work around fragile reefs.

It would be better to prevent the nets from becoming ghost gear in the first place by holding fishers legally responsible for their lost equipment and making disposal and recycling of nets easier and economically worthwhile, experts say.

Battling the problem of ghost gear requires knowing where it comes from, but data on how gear gets lost is sketchy. According to one survey of Australian and Indonesian fishers published in October in Marine Policy, about four fifths of lost equipment can be blamed on bad weather and one fifth of it gets tangled with gear set by other crews. Illegal fishers are also believed to be a major contributor to the problem, based on anecdotal reports, says Joanna Toole of the U.N. Food and Agriculture Organization (FAO). Unsanctioned fishing crews are likely to dump gear to avoid detection by authorities, and to dispose of worn-out items by simply throwing them into the ocean. Another problem, Dixon says, is recycling or trash facilities are not accessible at many harbors.

To combat these issues and help get a better handle on where ghost gear comes from, this past summer the FAO issued its first-ever guidelines for national governments on labeling fishing materials—in a way that “gives you the ability to track the gear all the way back to the manufacturer,” Toole says. But adopting the guidelines is voluntary, and they do not specify how equipment should be labeled. Where guidelines already exist, they can vary widely: The European Union, for example, requires tags with port letters or vessel numbers to be attached to buoys or gear; U.S. rules change from region to region, some stricter than others.

Gear-marking can be helpful in places like the Maldives islands in the Indian Ocean—where nets often drift in from other jurisdictions—because it helps focus regulatory and cleanup resources on the actual sources of the pollution, says Martin Stelfox, CEO of the U.K.’s anti–marine debris Olive Ridley Project and a researcher at the University of Derby in England. But labeling alone will not stop illegal fishing crews from creating ghost gear, he says, “If they’re illegal fishers, they’ll just remove that tracker, so you’re back to square one.”

Toole argues gear marking could theoretically help combat illegal fishing and its ocean litter. If unmarked gear is discovered in an area with gear-marking rules, it “rings alarm bells” that something illegal is happening, she says. But for those alarm bells to matter, someone has to be listening. Countries with poor fisheries management are going to have to improve their regulations and enforcement across the board, says Eric Gilman, who researches the ecological effects of fisheries at Hawaii Pacific University and consulted on the drafting of the FAO guidelines.

Labeling isn’t the only anti–ghost gear effort afoot. In Vanuatu the GGGI is helping attach GPS devices to keep tabs on large floating nets called “fish aggregating devices.” These nets are anchored to catch open-sea fish such as tuna but can slip from their moorings and end up adrift in knotted, car-size masses.

The GGGI is also working to help major fishing countries such as Indonesia set up trash-collecting and recycling facilities at harbor sides. Last month the organization announced a goal of getting, each year, at least as much ghost gear out of the ocean as goes into it by 2030. In Chile a separate campaign called Net Positiva works with small-time fishers and large commercial fisheries to collect and recycle nets into plastic pellets that can be used to make skateboards, office furniture and outdoor gear. So far Net Positiva recycles about 200 tons of fishing nets a year, co-founder Ben Kneppers says. He hopes to boost that to 1,000 tons annually within a few years.

Similarly, a project called Net Works—run in the Philippines by the Zoological Society of London—collects used nets and sells them to a U.S. company to be turned into carpet tiles. The project provides an economic incentive for poor fishing communities that lack waste management systems to keep their used nets out of the ocean.

For landlubbers who will never have to learn the difference between a seine and a gillnet, consumer pressure can prompt grocery stores and seafood retailers to clean up their suppliers’ acts, Dixon says. She and other experts point to fixes needed all along the seafood supply chain. “There’s no silver bullet to this,” Kneppers says. “It has to be a movement.”