Tuna fishing devices drift through a third of oceans, harming corals, coasts: Study

A recent study reveals that drifting fish aggregating devices (dFADs), widely used in tuna fishing, have spread to more than a third of the world’s oceans.  These devices harm ocean life and coastal communities, but weak rules and lack of accountability make it hard to manage them properly, some conservationists say.

The study, published in May in Science Advances, estimates tuna boats deployed 1.41 million dFADs between 2007 and 2021. They drifted through the waters of 157 countries and across at least 134 million square kilometers (nearly 52 million square miles) — about 37% of the world’s oceans. Many were lost at sea and stranded in 104 maritime jurisdictions, the study showed, polluting coastlines and harming marine habitats.

“Stranded dFADs can cause local habitat loss and pollution, especially where they involve the use of plastic netting, which is now being phased out,” study co-author Boris Worm, a marine ecologist at Dalhousie University in Nova Scotia, Canada, told Mongabay via email. “Cleaning up stranded dFADs can be very costly, and so far no progress has been made to make companies liable for the damage their devices cause.”

Stranded dFads

dFADs are floating rafts with underwater netting used by tuna purse seiners to attract skipjack, yellowfin and bigeye tuna (Katsuwonus pelamis, Thunnus albacares and T. obesus). The tuna school around such floating objects in pursuit of the prey that gather in their shade. One vessel can deploy hundreds of dFADs annually. Fitted with GPS and echo-sounder buoys, they drift with currents for weeks or months, allowing fishers to track and assess fish aggregations in real time, then capture them en masse.

Tuna industry groups say the use of FADs is vital for efficiently catching tuna — a key global protein source — while meeting the rules for regional fisheries management organizations (RFMOs) and supporting eco-certified selective fishing practices.  Europêche, the EU’s main fishing industry trade group, argues that advanced FADs improve catch precision, lower bycatch and vessel fuel use and emissions, support scientific research, and contribute to economic development in both Europe and the island nations in whose waters the European tuna fleet fishes.

The study analyzed data on dFAD use from RFMOs, the London-based eco-certifier Marine Stewardship Council (MSC), scientific studies and other public sources. It found that dFAD strandings were most frequent in key tuna fishing regions, especially the Indian and Pacific oceans. The Seychelles, Somalia and French Polynesia accounted for 43% of all recorded cases.

Worm recalled visiting French Polynesia in 2024, where numerous dFADs had stranded on coral reefs, breaking corals. Local communities and grassroots groups were left with the difficult work — and great expense — of cleaning them up.

“The fact that these impacts might occur thousands of kilometers from the actual fishing grounds makes it impossible to trace them back and assign some accountability,” Worm said.

Glen Holmes, a marine ecologist and an international fisheries expert with the U.S.-based Pew Charitable Trusts, called the study a strong “one-stop shop” for understanding three decades of dFAD fishing that spotlights key issues with RFMO regulations and the MSC certification process.

He noted that one of the biggest challenges in compiling such research is gaining access to data — an issue common across all international fisheries. This, along with data gaps acknowledged by the researchers, likely makes the findings conservative and limits precise estimates of dFAD deployments and impacts.

“The authors have done a good job in pulling what they can from publicly available data and made logical estimations to fill in the gaps,” he told Mongabay by email. “They also acknowledge the limitations of their approach, but it is logically presented and I can’t fault it.”

Environmental impacts

The study also highlights how dFADs have transformed tuna fishing by increasing juvenile catches, raising concerns about long-term stock sustainability. And it notes that the rapid rise of dFAD use in the 2000s may have conditioned tuna to associate floating objects with food, potentially altering their natural feeding, migration and schooling behaviors.

According to the researchers, dFADs disrupt open-ocean ecosystems by changing animal behavior and habitat structure, and, contrary to the claims of groups like Europêche, they actually increase bycatch of non-target species. Sharks and rays are especially vulnerable due to widespread fishing pressure and sharp global declines. Corals are also harmed when stranded dFADs cause entanglement, smothering and physical breakage.

“Both shark and rays as well as corals are slow to recover from additional mortality and their loss can affect tropical ecosystems and economies profoundly,” Worm said.

Researchers warn that dFAD strandings increasingly threaten biodiversity hotspots and marine protected areas (MPAs), with five of the top 20 affected jurisdictions being protected zones. Since drifting dFADs aren’t classified as “fishing,” vessels can catch aggregated fish once the devices leave protected zones, which undermines regulations and fuels illegal, unreported and unregulated (IUU) fishing, the paper notes.

Solutions to date

Despite decades of warnings and discussions at RFMO forums, concrete action to reduce dFAD impacts remains limited, the study notes. Governments began advocating for scientific regulation or bans on dFADs as early as the 1990s. However, key measures, such as capping the number of active dFADs per vessel, weren’t introduced until 2017. Still, there are no hard limits on how many dFADs a vessel or company can deploy each year, according to the study.

Seasonal fishery closures have been the main tool used by RFMOs to reduce juvenile overfishing, but despite urgent calls — especially in the Indian Ocean where juvenile tuna catches remain high — no seasonal ban has yet been implemented, according to the researchers.

Meanwhile, efforts to mitigate the impacts of lost dFADs have prioritized making the devices non-entangling and biodegradable rather than limiting their overall numbers at sea. Although growing NGO and industry concerns about bycatch, ghost fishing and plastic pollution have driven this shift, a timeline for full adoption remains unclear. “The next steps are working toward dFAD deployment limits and ensuring more dFADs are actually retrieved at sea and not left to drift away from fishing grounds to strand or sink,” said Laurenne Schiller, study lead author and postdoctoral fellow at Dalhousie University.

Despite the concerns, the study shows that MSC, the most prominent seafood eco-certifier, has made a striking uptick in certification of dFAD fisheries since 2020. While MSC certification purports to promote better fisheries management, it focuses on individual companies rather than entire dFAD fisheries, overlooking cumulative environmental impacts across ocean basins, the paper notes. Schiller said the MSC doesn’t comprehensively assess damage to coral reefs and other coastal habitats when certifying dFAD tuna fisheries — a gap she said needs to be addressed.

However, fishing industry representatives push back on the notion that dFAD use should be limited. “We do not believe that purse seiners should move away from FAD fishing, which is highly regulated in all RFMO[s], and fundamental in terms of food security,” Europêche Tuna Group director Anne-France Mattlet told Mongabay via email. She added that phasing out dFADs would unfairly disadvantage European fleets, which operate under strict social, environmental and monitoring standards not required of competing fleets.

Closing regulatory gaps

Regulatory gaps in dFAD management persist partly due to political differences within RFMOs, where some member states prioritize economic interests and at times challenge or weaken proposed rules, delaying stronger tracking and accountability measures despite scientific recommendations, the paper notes.

Schiller and Worm said that although market pressure has improved tuna fishery management, companies remain largely unaccountable for dFAD damage due to limited requirements that they register their devices or mark them so they’re traceable to their owner.

Currently, the cost and effort of removing stranded dFAD debris fall on the affected country or community, highlighting a major gap in dFAD management, Schiller said.  “Moving toward clear dFAD ownership rules and responsibilities combined with regional dFAD registries would really help when it comes to improving accountability,” she added.

The study highlights early progress on dFAD tracking, such as the world’s first registry launched by the Parties to the Nauru Agreement in 2022 and a similar move by the Indian Ocean Tuna Commission set for 2026. However, adoption by other RFMOs remains uncertain. Researchers urge a global framework with stricter deployment limits, full observer coverage, better rules to reduce beachings and abandonment and standardized reporting across all RFMOs.

“Clearly, these devices have a near-global impact on one of the largest and least well-understood ecosystems on our planet: the open ocean,” the paper notes.

Banner image: Drifting fish aggregating devices often strand in regions far away from tuna fishing grounds, leading to coastal pollution. This one, found on a beach in Texas, was likely deployed off the coast of West Africa. Image courtesy of Jace Tunnell.

Citation:

Schiller, L., D’Costa, N. G., & Worm, B. (2025). The global footprint of drifting fish aggregating devices. Science Advances, 11(19). doi:10.1126/sciadv.ads2902

FEEDBACK: Use this form to send a message to the editor of this post. If you want to post a public comment, you can do that at the bottom of the page.

Credits

Rebecca Kessler Editor

This story first appeared on Mongabay

This article is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.

You may republish this article, so long as you credit the authors and Mongabay, and do not change the text. Please include a link back to the original article.