NEW YORK -- The vulnerable stocks of bigeye tuna beloved by sushi fans face an even deeper threat as the juveniles become an unintended casualty of weakly regulated buoyed devices that lure vast numbers of fish, the Pew Charitable Trusts said ahead of World Tuna Day on Wednesday.
No one knows how many of these fish aggregating devices, known as FADs, are scattered across the oceans. The devices, which attract plentiful skipjack tuna like moths to a flame, allow purse seines to scoop up massive quantities of fish at once. But they also can catch the young of more endangered species like bigeye and yellowfin tuna in the process.
"FADs have increased the mortality of juvenile bigeye, so they're being caught before they have a chance to reproduce and grow into adult fish," Dave Gershman, an officer at Pew's global tuna conservation program, told the Nikkei Asian Review. "You can be dealing with 100 tons of tuna in that one school, so it's difficult to separate out the fish by species."
Japan catches the most adult bigeye tuna, snaring 12,610 metric tons in 2016. South Korea, Taiwan and mainland China follow, while the U.S. ranks fifth. Threats to the bigeye population would trouble sushi lovers, who could lose the lean meat from many of their favorite dishes.
The aggregating devices have been controversial for years, with some conservationist groups such as Greenpeace advocating for an outright ban. Pew does not oppose the use of FADs, suggesting that they improve the efficiency of skipjack fishing, which helps those employed in the industry and provides a food source for many people.
"But like with any other fishing gear, FADs need to be managed appropriately," Gershman said. "And the international organizations ... have been slow to look at the impacts of FADs and manage them appropriately."
Fishing companies that deploy the devices track their own use, but they are not required to share data with the regional fishery management groups that set bigeye catch regulations.
One such group, the Western and Central Pacific Fisheries Commission, enacted closure periods: timed, temporary bans on the deployment of the devices. But after receiving optimistic data on bigeye stocks last year, the commission raised catch limits and reduced the closure periods.
Pew thinks the commission "went too far in relaxing controls" on bigeye fishing, Gershman said, and ignored scientific advice calling for stricter catch limits to maintain healthy stock levels.
The fisheries commission meets again in December to consider stock management, which Pew views as a chance to discuss FAD regulations. Gershman sees a limit on the number of times a vessel can use the devices as one potential fix.
Recent progress has been made regarding data collection, Gershman said, as more fisheries join a trial tracking and monitoring program. The data sharing platform came from the eight Pacific island countries that formed the Nauru Agreement focusing on tuna supplies.
"We're hopeful that the analysis of this data will yield some new insights into FADs and the behavior of the FAD fishery," Gershman said. Pew provided funding to a company that is developing software for this program.
The United Nations designated May 2 as World Tuna Day in 2016 to boost awareness of the global importance of tuna and the challenges the fish face.
"The day seeks to recognize the critical role of tuna to food security, economic opportunity, and the livelihoods of people around the world," Farhan Haq, deputy spokesman of the UN Secretary-General said on Wednesday. "Tuna species account for 20% of the value of all marine capture fisheries and over 8% of all globally traded seafood, and as a result, the fish are threatened by an overwhelming demand."