Experts raise concerns about damage to fish stocks by aggregation devices

Canadian researchers are warning of the impacts of drifting fish aggregation devices commonly used across the globe in commercial tuna fishing.

They say improvements to FADs and their mass deployment are having detrimental impacts on vulnerable marine species.

Fish aggregation devices (FADs) float on the ocean’s surface, or just below and cast a shadow. This attracts fish, particularly in the open ocean where shelter is scarce.  Smaller fish congregate, attracting larger predators and so it goes on.

Fishermen have always used natural FADs, such as free-floating logs and even large marine mammals such as whale sharks. Anchored FADs (aFADs), are also common, supporting subsistence and commercial fisheries, in many parts of the world, including the Pacific islands.

It is the FADs designed to drift (dFADs), that have researchers concerned. These can be entangling, with nets hanging into the water column or non-entangling, with rolled up nets or ropes used, says the Marine Stewardship Council. 

Lead author of a paper published in Science Advances, Laurenne Schiller of Canada’s Dalhousie University in Halifax, Nova Scotia, says technological advances since the 1990’s have led to large-scale deployment of dFAD rafts by tuna fisheries. Installed global positioning systems (GPS) and high-resolution echo sounder satellite buoys also let purse seine fishers know what and how much they might catch beneath each dFAD.  

A purse seine vessel circles a target school using a net that hangs like a curtain in the water — with floats on the top and weights on bottom. Once surrounded the tuna are trapped as the crew pulls on a drawstring running through the net’s bottom, closing it like a purse.

Purse seiners may have 500 dFADS on-board, with 200 licenced to be deployed at any one time, says Bill Holden, Senior Tuna Fisheries Outreach Manager at the Marine Stewardship Council (MSC).

Holden says about 50% of vessels in the Western and Central Pacific Commission Regional Fisheries Management Organisation (WCPO) use dFADS. This region includes Australia and New Zealand and many of the other nations in or bordering on that stretch of ocean.  

This industrialisation of dFADS may be having major impacts on at-risk species say Dalhousie researchers.

Schiller and her team tracked the global distribution of dFADs and looked at how regulations had changed over the last 30 years. Around 1.4 million FADs were deployed between 2007 and 2021, ranging across about 134 million square kilometres, or 37% of the ocean surface, she says. Strandings were also common, says Schiller; abandoned dFADs with broken GPS trackers were concentrated the Seychelles, Somalia, and French Polynesia.

Drifting FADs may be changing pelagic open-ocean habitats, and the behaviour of many of its inhabitants, says Schiller, with little action being taken to halt or reverse this trend, she adds.

Holden disagrees that there is ‘little action’.

“Industry, is often ahead of the curve.” In the WCPO, it’s 100% observer coverage. So we’re really lucky in this region. And for MSC-certified fisheries, in the Indian Ocean and the Atlantic Ocean, they voluntarily do 100% observer coverage. In the eastern Pacific they mandate 100% observer coverage for the larger purse seiners.” 

Observers, are independent specialists onboard to monitor fishing operations, including overfishing, by-catch and interactions with threatened, endangered and protected species. In Australia the program is run by AFMA, the Australian Fisheries Management Authority.

“Fifty-one percent of WCPO commercial tuna catch is MSC-certified. Globally its 54%,” says Holden.

“MSC certification only includes commercial tuna stocks (albacore, bigeye, bluefin, skipjack and yellowfin) as there are many minor tuna stocks (ie bullet tuna, longtail tuna, slender tuna etc) that are more or less inshore artisanal stocks.

“It’s an expensive game,” Holden says, “There’s not so many cowboys anymore in the purse seine industry. Vessels cost $25 million and there’s crew to hire and provisions to buy and other expenses.

“You’re seeing the less efficient, less economical purse seiners drop out of the out of the industry.”

Compliance within industry is also getting tighter. Many vessel owners are installing video cameras on board, to catch shark-finning and other illegal practices, says Holden.

Dealing with dFAD impacts is a work in progress.

“Our results demonstrate that the cumulative environmental footprint of dFADs reaches far beyond tuna fishing grounds and remains inadequately mitigated at the global scale,” says Schiller. Regulating dFADs can also be challenging, she adds, as multiple countries fish for tuna within the same ocean and agree on management can be difficult.

Schiller calls for reductions in the impacts of dFADs on marine ecosystems, particularly the unsustainable bycatch of nontarget species, and pollution and damage to marine life from disintegrating, nonbiodegradable rafts.

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