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A Life Sentence For Yellowfin And Bigeye Tuna

Written by Megan Bailey, PhD student at the Fisheries Center at the University of British Columbia in Vancouver, Canada
Sixty percent of the world's tuna catch comes from the western and central Pacific Ocean, and skipjack makes up almost 70% of that catch. Fishers often use purse seine nets and fish aggregating devices (FADs) to catch skipjack, taking advantage of the propensity of tuna, and other marine species, to gather around floating objects. Some are simply a few logs tied together, while others are complicated devices with sonar and radar capabilities. Recent video footage and some media reports have raised a major sustainability issue associated with FAD fishing: by-catch of juvenile tuna and non-tuna species such as swordfish and dolphinfish.
Skipjack are fast growing, but yellowfin and bigeye tuna don't mature until individuals are upwards of 1 m in length. Juvenile tuna associate with skipjack stocks under FADs, and are harvested when they are only 15 to 20 cm in size. Up to 100% of purseseine caught bigeye is immature. This leads to a phenomenon that biologists call growth overfishing. When fish are captured too young, they are not able to reach the size that produces the maximum yield. This is economically wasteful, representing a loss of potential future harvest, but because the tuna are caught before they can reproduce, growth overfishing also hurts the long]term ability of the population to thrive.
Juvenile yellowfin and bigeye are sold to canneries along with harvested skipjack. If left in the ocean to grow and mature, those tuna could end up being targeted as adults by pole and line or longline fishers. Adult tuna are worth more per kilogram to fishers, and they have had the chance to reproduce. You would have to remove more than 20 times as many juvenile tunas to catch the same weight in adults. FADs seem to make economic sense. It is far less costly to make the fish come to you (or your FAD) than having to go find the fish. But this is a very short term economic view, as future sustainability, and thus future economic return, is at stake.
Simulation studies we have developed at UBC suggest that there are real ecological and economic benefits possible from solving the growth overfishing problem, writes Megan Bailey in Fishing News International.
Purse seining is probably here to stay because people want canned tuna. But there are more ecological ways to do it that are also more economically sustainable. One such way is to set purse seine nets on schools of tuna that are not associated with floating objects (called unassociated schools), as long as there are also strong restrictions on setting nets on other vulnerable marine species, such as whale sharks and dolphins.
When considering your can of tuna, you have a couple of options. The first is to actually eat less tuna, because global demand really does influence fishing methods. Secondly, you can pressure tuna companies to source their inputs from sustainable fisheries. FAD use needs to at least be regulated, which has not been an international priority of yet. Better still, FADs should be eliminated. The purse seine FAD fishery is jeopardizing the ability of the western and central Pacific Ocean to continue providing the majority of global tuna supply, and supporting the livelihoods of tuna fishers in over thirty countries. Managers and governments would be wise to expand their time horizons to better appreciate how myopic policy decisions threaten ecosystems and economies.