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VIET SEAFOOD

Don’t Catch Only Tuna Global, March 6, 12

Balanced Fishing Is More Ecosystem-Friendly, Say Scientists
Balanced fishing could be better for ecosystems than current sustainable practices that target mature tuna and limit by-catch, according to a recent report published in Science Magazine.

Researchers found that fishing for the largest possible range of species, stocks, and sizes, both maximizes the total catch weight and maintains the structure of the ecosystem. Under this less selective approach, by-catch would no longer be “an operational nuisance,” but a valuable product.

“The idea is that much of the by-catch could actually be retained and sold,” says Paul van Zwieten, a fisheries management professor at Wageningen University in the Netherlands.

There are a number of species caught accidently with FADs, such as mahi-mahi and rainbow runner, that are already being retained and increasingly utilized, he says. The focus should now be to find or create new markets for these viable fish.

“You shouldn’t see yourself just as a tuna fisherman anymore. You should start thinking that you are fishing a range of species,” he says.

The report, “Reconsidering the Consequences of Selective Fisheries,” examined 36 ecosystem models and compared the effects of conventionally selective, unselective, and balanced fishing methods. The results indicate selective fishing does not maximize the total yield available and it only conserves biodiversity when fishing catches are negligible and with little profit.

Exclusively targeting large mature fish should therefore be reduced, according to the report, because it destabilizes the aquatic community by affecting population size and composition. Continuous fishing for large fish could also cause genetic changes in the stock, such as earlier maturation and smaller adult growth.

“Ecologically speaking, it’s not a problem to catch juvenile fish. But for many fisheries, it’s an optimization problem; you earn more if you catch a larger tuna. Economically speaking, it’s better to wait until these juvenile fish grow a bit longer,” says van Zwieten.

Catching baby bigeye tuna would not be a problem if the total catch on this species was moderate, he says. Since a total harvest from a FAD fishery normally yields an average of 7% of bigeye as by-catch, the total catch of tuna must be reduced to yield unintentionally caught bigeye at a sustainable level.

With the bigeye stock’s current overfished state in the Western and Central Pacific, however, van Zwieten says catching it is a problem at the moment, no matter its size, that should be mitigated. He could not say how to avoid catching these fish, but he did say the fishing pressure on tuna would decrease if all the by-catch was retained and sold in a balanced fishery.

“If you have the same number of boats and their hulls are being filled earlier with all kinds of fish except tuna, then instead of a full boat of tuna, you only have half a boat of tuna.”

It’s clear that if these scientists get their way, fisheries would catch less tuna and consumers would be introduced to the diverse tastes of so-called “by-catch.”
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