The tuna in your sandwich was likely caught with the help of drifting rafts called fish aggregating devices, or FADs. New Canadian research finds that abandoned FADs are smashing into coral reefs and endangering wildlife — even in marine protected areas. But there are ways to make tuna fishing more sustainable.
Drifting FADs have entered more than 1,500 or half of the world’s marine protected areas, meant to protect vulnerable species, despite bans on fishing in those areas, estimates the new study published this week in Science Advances.
What are FADs and how are they used in tuna fishing?
Drifting FADs are used to catch smaller tropical tuna, especially skipjack, that is sold in cans.
The floating rafts are made of wood or bamboo with plastic elements and they’re about the size of a boardroom table, said Boris Worm, marine conservation professor at Dalhousie University and co-author of the new study.
Traditionally, nets or ropes are hung underneath them to a depth of about 80 metres to attract fish and slow their drift. But because mesh nets entangle wildlife, they were banned on FADs worldwide in 2025 and replaced with just ropes.
The rafts attract small fish that seek them as shelter, like driftwood. That makes schools of predators like tuna gather, so they can be more easily and efficiently netted and caught by a fishing boat.
FADs are generally equipped with a plastic GPS buoy and a fish detector. Fishing boats can return and fish near them with a purse seine net once enough fish have gathered underneath.
About 100,000 FADs are released into the ocean in each year, and about 90 per cent eventually get lost, said Worm: “The problem is they’re sort of expendable.”
FADs are typically in use for about a year, said Hilario Murua, director of science for the International Seafood Sustainability Foundation (ISSF). But they can continue to drift through the ocean for up to five years after that, although most strand or snag somewhere in that time.
What problems can they cause in protected areas?
When FADs drift into marine protected areas, they can strand on beaches and in coral reefs, causing damage and plastic pollution, said Laurenne Schiller, postdoctoral researcher at Dalhousie University and lead author of the new study.
The study documented more than 6,000 strandings of FADs in 174 protected areas.
Schiller said people who work there described the rafts “hitting corals and just shearing off large chunks of coral in many protectors or getting stuck and … going back and forth and just breaking corals.”
She added that many marine protected areas host rare and threatened coral species.
Sharks and turtles have also become entangled in FAD netting, which hopefully will happen less now. “It’s really great progress that these nets are no longer permitted,” said Schiller, although some older FADs with netting are still drifting through the ocean.
Ultimately, FADs become waste. The study found they tend to accumulate in certain hot spots, such as French Polynesia, the Seychelles and the Maldives. On beaches, the litter poses a problem for wildlife such as nesting sea turtles.
“It actually prevents the turtles from either being able to dig a nest or the baby turtles from getting to the ocean,” Schiller said.
Local communities often end up doing the costly, difficult cleanup. That’s partly because fishing companies worry about being accused of illegal fishing if they go into a marine protected area to retrieve a FAD. Schiller said that’s a legal issue that needs to be addressed.
The study was funded by Pew Charitable Trusts, which has raised concerns about the impacts of FADs, and the Natural Sciences and Engineering Research Council of Canada.
What can be done to reduce their impact?
Sustainability certifications such as Marine Stewardship Council (found on the label of tuna cans) have been a “huge incentive” for fishing companies to make improvements such as reducing or removing netting (even before regulations came into place), or using more biodegradable materials, Schiller said.
The International Seafood Sustainability Foundation helps tuna fisheries implement best practices for sustainability certification. It recently released a design for a completely biodegradable (except for the GPS buoy) “jelly FAD” made of bamboo and cotton, and inspired by the neutral buoyancy of a jellyfish. The ISSF’s Murua says its smaller size also reduces its impact when it strands.
Murua agreed that FADs cause marine pollution that needs to be addressed, but he said now that FADs are designed not to entangle wildlife, they won’t necessarily have an immediate impact on species in marine protected areas even when they drift there.
Schiller and Worm also recommend limiting the total number of FADs deployed, avoiding release where they’re likely to strand and encouraging retrieval of old ones at fishing companies’ expense.
A Spanish fleet near the Seychelles is already doing that, said Adrian Gutteridge, senior fisheries standards manager for the Marine Stewardship Council, with a designated buffer zone between their fishing ground and local coral reefs. When FADs enter, either they will retrieve them or alert local environmental organizations.
He added that research like the new study helps direct how to better mitigate the environmental impacts of FADs, since MSC requirements are updated regularly, and fisheries need to publicly show they’re improving on these measures to maintain their certification.
Worm noted that some years ago when dolphins were being entangled during tuna fishing, public awareness pushed the industry to quickly fix the problem. Similarly, he said with the impacts of FAD fishing, “the more people that know about this, the better.”
