TOKYO -- Unexpectedly large numbers of Pacific bluefin tuna have been winding up in nets set off Hokkaido, raising concerns that Japan will exceed its quota for the endangered fish.
The prized fish are being caught in fixed nets placed for salmon, yellowtail and other fish.
Japan's overall bluefin catch so far this year has been twice as large as in ordinary years. It is on track to exceed the overall quota imposed by an international regulatory regime trying to ensure that the bluefin population recovers.
Years of overfishing have put bluefin on the endangered list.
In early October, bluefin began unexpectedly arriving in nets off the coast from the city of Hakodate. Fishing vessels leave the port there at around 3 each morning. In about 15 minutes they reach especially rich fishing grounds, where their set-nets stretch for several hundred meters.
The nets are meant for less expensive salmon, cuttlefish and other marine life, but on some days so many bluefin get trapped that they suffer skin lesions from rubbing against one another.
"I have been fishing for 40 years around here," one fisherman said, "but I have never caught so many bluefin."
The quota is applied to bluefin weighing less than 30kg. So far, 600 tons of small bluefin have been netted off Hokkaido. This exceeds Japan's quota for bluefin caught in nets for the year through next June, which is slightly over 580 tons. The catch off Hokkaido alone could surpass Japan's overall bluefin quota, which includes rod-and-line and other fishing methods.
Fish wholesalers are struggling to deal with the situation. In early October, "we began receiving shipments of hundreds of small bluefin every day," said a major wholesaler operating at Tokyo's Tsukiji fish market.
Bluefin caught beyond the quota wholesale for 400 yen to 600 yen ($3.50 to $5.30) per kilogram. This is less than half what ordinary small bluefin fetch -- 900 yen to 1,200 yen.
Some of the "irregular" caches have been sold directly to supermarkets instead of being auctioned off.
Each country's quota is determined by the Western and Central Pacific Fisheries Commission, a treaty-based international body for conserving and managing stocks of tuna and other migratory fish in the western and central parts of the Pacific.
Unintended catches with set fishing nets are not exempted from the quota.
Currently, Japan only keeps tabs on the total annual national catch its fishermen make with set-nets. Under this system, rich hauls in some areas early in the fishing year can force other areas to limit their catches. This could give fishermen a sense of unfairness.
The Fisheries Agency is thus considering setting a quota for each prefecture.
Some fishermen are working to develop devices and schemes to allow unintentionally netted bluefin to escape.