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Study reveals large environmental footprint of fish aggregating devices used by industrial tuna fisheries, proposes steps to address impacts

Wednesday, May 7, 2025 (Halifax) __ Most consumers enjoying a tuna salad or sandwich are not aware that the fish they're eating is often caught with the help of a device that can cause unintended harm to imperiled marine species and ecosystems.

Introduced in the 1990s to produce ‘dolphin-safe’ tuna, drifting Fish Aggregating Devices (dFADs) have now become so common that research shows they pose pervasive environmental risks at a vast scale. A comprehensive study in Science Advances has now detailed their impacts and shows where and how such harms can be addressed.

DFADs are large satellite-tracked rafts, traditionally equipped with long submerged nets, that attract fish in an otherwise featureless ocean environment. Used most often to catch skipjack tuna -- the species caught at the highest rates globally -- these devices drift over thousands of kilometres and facilitate the formation of schools of fish that can then be scooped up by industrial tuna fishing vessels.

The study, by researchers at Dalhousie University, Carleton University and Manta Trust, estimates that 1.4 million devices were released between 2007 and 2021, and used to help catch nearly one-third of the world’s tuna during this time. The research shows that more than 90 per cent of some tuna species are not yet mature when caught because smaller fish are more likely to seek shelter under the raft.

The study also reveals that lost devices have washed ashore in more than 100 coastal countries, contributing to marine pollution and damaging coral reefs.

The magnitude of these impacts surprised researchers.

"We found that these devices have drifted through at least 37 per cent of the global ocean — an area as large as all inhabited continents combined. Yet most people have never heard of dFADs because tuna fishing occurs mostly in the tropics," says study lead author Laurenne Schiller, a postdoctoral research fellow at Dalhousie and Carleton.

The authors also document that concerns about the growing use of dFADs have been voiced by scientists, regulators and the fishing industry for more than 20 years.

Tropical tuna fisheries are managed through four Regional Fisheries Management Organizations, or RFMOs, and progress to address concerns has historically been slow but is increasing, say the authors. Since research and regulation of dFADs occurs mostly at a regional scale, this study represents the first attempt to present a global overview.

"Because the ocean is all connected, there are no boundaries for dFADs in their global travels and their impacts are often felt far from where they were initially deployed. We need to consider how many devices can be in the water at once and make sure they all get retrieved," says senior author Boris Worm, a marine ecology professor at Dalhousie.

Transparency and accountability are major problems, according to the study, which calls for better labelling of dFADs so that any damage they cause can be traced back to a fishing vessel or company. It will also help to identify responsible fisheries that are adhering to the conditions for Marine Stewardship Council sustainable seafood certification, a coveted eco-label held by most tuna fishing companies.

The authors show that many fisheries that use dFADs have recently been certified, but most have open conditions related to minimizing ecosystem impacts.

"Programs like the MSC can really motivate companies to improve their practices, but it's also important that this improvement is continuous and doesn't just end with certification," says Dr. Schiller. "In the case of dFAD tuna fisheries, many companies still have a lot of work to do and consumers should be aware of that."

The authors are hopeful that progress can be made and have documented comprehensive management measures that have been proposed or are already implemented to lessen the impacts of this fishing method.

"Most dFADs are deployed by a few large companies from wealthy countries, but their effects are felt across some of the world's least developed island nations with little capacity to address the damage that is caused," says study co-author Nidhi D’Costa, a fisheries researcher from Bangladesh now working for the Manta Trust:

More information, including a copy of the paper, can be found online at the Science Advances press package: https://www.eurekalert.org/press/vancepak/

Photos are available here.

Author contacts, languages and expertise:

o   Laurenne Schiller (English) – international fisheries, legislation and governance, public perception and market pressure on fishing companies
Email: laurenne.schiller@dal.ca
Phone: 1-902-414-8466 (Pacific time)

o   Boris Worm (English, German) – Marine fisheries and conservation
Email: bworm@dal.ca

o   Nidhi D’Costa (English, Bangla): Marine fisheries, policy and management, community-based conservation
Email: nidhi.dcosta@mantatrust.org

Media contact:

Alison Auld
Senior Research Reporter
Dalhousie University  
Cell: 1-902-220-0491  
Email: alison.auld@dal.ca