Bluefin getting smaller in Tottori port's catch

TOTTORI (Kyodo) The average weight of bluefin tuna caught in the Sea of Japan and brought to a port in Tottori Prefecture is less than half of what it was 25 years ago, according to local statistics.

Not what they used to be: Tuna are hoisted from a fishing boat at the port of Sakaiminato, Tottori Prefecture, in July. KYODO PHOTO

Experts suspect overfishing resulting from improved technology has contributed to the significant weight decline observed at Sakaiminato port.

Advanced sonar technology allows fishermen to target schools of tuna, including young fish in spawning season.

"Large tuna are rapidly vanishing and overfishing is strongly suspected. We need to have some kind of regulation or it could affect their reproduction," said Toshio Katsukawa, an associate professor and expert on marine resources at Mie University.

A decrease in the size of bluefin became an issue in the Atlantic Ocean in the 1990s, and Katsukawa said this is the first finding of its kind regarding tuna in the Sea of Japan.

He called for setting an upper limit on catches because roll-net fishing common in the area "has a significant impact on (marine) resources."

Bluefin catches reported at Sakaiminato account for 10 percent to 20 percent of Japan's total haul.

In the past, less than 10,000 bluefin tuna were brought to Sakaiminato annually, but the number has increased to between 20,000 and 40,000 since fiscal 2004, according to local statistics.

The weight of the fish, on the other hand, has gone down over the years, with the average tuna weighing in at 110 kg to 160 kg in the early 1980s but weighing less than 70 kg in the 1990s and as little as 44 kg in 2007.

While the trend will probably continue, the city of Sakaiminato has declined to disclose data for fiscal 2008, saying it does not want to mislead people into thinking the fish are being caught recklessly.