Japanese call bluefin tuna “the king of fish”. They eat about 40,000 tonnes of it a year—80% of the global catch. Demand is also growing rapidly elsewhere. Yet Pacific bluefin stocks are down by 97% from their peak in the early 1960s, according to a recent report from the International Scientific Committee, an intergovernmental panel of experts. (Japan disputes its findings.) In some places, fishing is three times the sustainable level, the committee says.
Aquaculture might seem to offer a way out of this impasse. But the bluefin is hard to breed in captivity. In the open sea, it can roam for thousands of miles and grow to over 400kg. It is highly sensitive to light, temperature and noise. Early attempts to farm it fizzled, but Kindai University persisted long after an initial research grant from the government ran out in the early 1970s. In 2002, funding itself from sales of other fish, it managed to rear adult tuna from eggs for the first time, rather than simply fattening up juveniles caught at sea. Now the chefs in Ginza can have a tuna zapped with an electric prod and yanked out of the university’s tanks on demand.
However, just 1% of the bluefin the university rears survive to adulthood. “We expect this to improve but it will take time,” predicts Shukei Masuma, the director of its Aquaculture Research Institute. Worse, the tuna gobble up lots of wild mackerel and squid. Scientists have experimented with soy-based meal and other alternatives. A company in south-western Japan said this month that it had managed to raise tuna using feed made of fishmeal, but it is costly and the fish are slow to thrive. Using wild fish for feed makes bluefin farming unsustainable, says Atsushi Ishii of Tohoku University. He sees aquaculture as a distraction from the thorny task of managing fisheries properly.
This debate is slowly seeping into the public consciousness. In 2014 the media made much of the decision of the International Union for Conservation of Nature, a conservation body, to put bluefin tuna on its “red list” of species threatened with extinction.
Excerpts from The Japanese Addiction to Tuna: Breeding Bluefin, Economist, Sept 24, 2016