The population of large Pacific bluefin tuna with reproductive capacity is shrinking at an alarming rate, and they may be facing a crisis similar to the one their Atlantic peers are facing, according to a recent study by Japanese researchers.
The results indicate the need to accelerate efforts to restrict the catch of both Atlantic and Pacific bluefin.
The study by a team led by Toshio Katsukawa, an associate professor and expert on marine resources at Mie University, also found that an overexploitation of large fish has led to a rise in the catch of small fish less than 3 years old that have yet to produce eggs.
“It is imperative to suspend the catch during egg production periods and reduce the capture of juvenile fish,” Katsukawa said. “If we wait to catch them until they get bigger, the resources will recover and the revenue of fishermen will also increase.”
Japan accounts for more than 70 percent of the bluefin tuna caught in the Pacific, of which about 55 percent are caught with encircling nets. In recent years, it has also become popular to catch young fish and breed them.
Estimates by Katsukawa based on the fish caught with encircling nets and the number being traded at Tokyo’s Tsukiji fish market found the average weight of bluefin is around 50 kg, compared with 100 to 160 kg in the 1980s.
The proportion of bluefin tuna aged less than 1 year among the fish caught stood at around 60 percent during the 1960s, but climbed to more than 70 percent after 2000.
The study indicates that the number of large fish aged 6 years or older that were caught by trolling has been declining dramatically since 2004, while the catch of bluefin using encircling nets fell sharply in 2009. The data reflect deterioration in marine resources, according to the study.
Meanwhile, the average annual value of tuna less than 2 years old stood at ¥2.7 billion on landing at ports between 2004 and 2008.
If the young fish are not caught until they reach 7 years old, the study estimates, the average value will jump to ¥223.5 billion.
According to the Fisheries Agency, Japan caught about 17,800 tons of Pacific bluefin and imported about 3,800 tons in 2008, nearly equivalent to the quantity of Atlantic bluefin consumed here.