Study shows steep drop in Pacific bluefin tuna

(Mainichi Japan) May 11, 2010 TOKYO (Kyodo) — The population of large-sized Pacific bluefin tuna with reproductive capacity is shrinking at an alarming rate, in a sign they may face 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 the Atlantic and Pacific bluefin tuna, which are consumed in massive numbers in Japan, for the protection of resources. The study by a team led by Toshio Katsukawa, an associate professor and expert on marine resources at Mie University, also showed that an overexploitation of large-sized fish has led to a rise in the catch of juvenile small fish below 3 years or before egg production. “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 over 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. According to estimates by Katsukawa based on the amount of fish caught with encircling nets and the number being traded at Tokyo’s Tsukiji fish market, the average weight of bluefin tuna is around 50 kilograms, far lighter than the average of 100 to 160 kg in the 1980s. The proportion of bluefin tuna aged less than 1 year old among the fish caught stood at around 60 percent during the 1960s, but climbed to over 70 percent after 2000. More recently, the combined proportion of fish of less than 2 years old has surpassed 90 percent. The study shows the number of large fish aged 6 years or older that were caught using the so-called pole-and-line fishing method has been dramatically declining 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. …