Tuna fishing gear is harming oceans more than we thought

Tuna fishing relies on rafts that drift for thousands of kilometers, silent and unmoored, following ocean currents across vast, empty waters.

These floating devices, often made with netting tails dangling beneath the surface, aren’t just drifting aimlessly – they’re designed to attract fish. Once surrounded by schools of tuna, the fish are scooped up by large industrial vessels.

Known as drifting Fish Aggregating Devices, or dFADs, these tools have been a staple of commercial tuna fishing since the 1990s.

They were created to help produce “dolphin-safe” tuna by reducing the need to chase tuna schools that often swim with dolphins. But these devices have brought along a new set of problems that stretch far beyond their original intent.

How far the devices really travel

Scientists from Dalhousie University have taken a closer look at how the aggregating devices are used and where they go. In a new global study, they tracked just how far these devices have traveled and how much damage they may be causing.

“We found that these devices have drifted through at least 37% 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,” said study lead author Laurenne Schiller.

The researchers found that dFADs have left a lasting mark on oceans across the globe.

“Our results demonstrate that the cumulative environmental footprint of dFADs reaches far beyond tuna fishing grounds and remains inadequately mitigated at the global scale.”

Tuna fishing gear pollution

The numbers are staggering. The team, which included researchers from the Manta Trust, estimates that 1.4 million dFADs were deployed between 2007 and 2021. These devices were used to catch nearly one-third of the world’s tuna supply.

In eastern Canada, fishers don’t typically use dFADs. The devices are more commonly used in tropical fisheries, particularly in the Pacific.

Unfortunately, many of these rafts don’t stay at sea. They often wash ashore in more than 100 coastal countries. Some are made of natural materials, but many are synthetic and contribute to marine pollution. As they break apart, they entangle marine life and damage coral reefs.

There’s also the issue of the tuna being caught. More than 90% of some tuna species are snagged before they reach maturity. That’s because younger fish are more likely to gather under floating objects.

Scientists and environmental groups have warned about these problems for over two decades. Fishing methods have shifted from chasing free-swimming tuna to targeting fish that gather near floating structures. That change has added new risks.

Why tuna chase rafts

Fish naturally seek cover. Floating debris, like logs or clumps of seaweed, can offer shelter in the otherwise open ocean. Tuna tend to gather under these objects, and that instinct is what dFADs exploit.

These artificial rafts have become essential equipment in tuna fishing – especially for skipjack, yellowfin, and bigeye tuna. Skipjack, in particular, is the type most often used in canned tuna.

Each dFAD can include a GPS tracker, which allows vessels to deploy the raft, leave it adrift, and return weeks or even months later. By then, fish have usually gathered beneath the device.

“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,” said senior author Boris Worm, a marine ecology professor at Dalhousie.

“We need to consider how many devices can be in the water at once and make sure they all get retrieved.”

Lack of global regulation

Tropical tuna fisheries are overseen by four Regional Fisheries Management Organizations (RFMOs). Historically, they’ve been slow to respond to the growing list of concerns.

Only recently have rules started to limit the use of netting in dFADs, to reduce bycatch of other marine animals like sea turtles and sharks.

Still, there are no global rules that limit how many dFADs a company can use. That lack of regulation makes it hard to hold anyone accountable when problems arise.

The researchers argue that transparency is a major issue. Right now, it’s difficult to trace where a dFAD came from or who deployed it. Better labeling is essential to track damage and improve responsibility.

In 2026, the Indian Ocean Tuna Commission will launch a new dFAD registry. Every device will be assigned a unique code that links it back to the fishing vessel. This step is expected to improve accountability across the board.

It may also help verify which companies meet the requirements for Marine Stewardship Council (MSC) certification – a label that many tuna brands use to market their products as sustainably sourced.

Reducing the impact of tuna fishing gear

The study revealed that while many dFAD-using fisheries now carry sustainability labels, most still fall short of meeting requirements related to minimizing damage to ocean ecosystems.

“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,” said 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 researchers remain hopeful that change is possible. Their study highlights several proposed solutions – some of which are already in place – that could lessen the environmental cost of tuna fishing gear.

Study co-author Nidhi D’Costa is a fisheries researcher from Bangladesh who is now working for the Manta Trust.

“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,” said D’Costa.

The full study was published in the journal Science Advances.

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