The International Commission for the Conservation of Atlantic Tuna (ICCAT) over the weekend reduced the eastern Atlantic bluefin tuna quota by nearly 40 percent for 2010, to 13,500 metric tons.
In Japan — which consumes about 80 percent of the roughly 60,000 metric tons of bluefin tuna caught worldwide annually — restaurateurs, retailers and consumers fear that the quota cut will cause prices to jump.
But with the recent reduction in consumption of expensive fish, including tuna, the quota cut is not expected to immediately lead to higher prices in Japan. Some supermarket chains have already switched to offering bigeye or yellowfin tuna in place of bluefin to keep prices down.
Hirotaka Akamatsu, Japan’s fisheries minister, said at a press conference on Tuesday that Japan has ample supplies of frozen tuna due to the recession.
“I want people to know that there is no reason to fear tuna prices will spike or that the inventories of tuna will run out,” he said.
Inventories of frozen bluefin tuna in Japan have increased yearly, and as of September there were about 24,600 metric tons in cold storage, about 10,000 metric tons more than a decade ago.
Another concern is that the quota cut will encourage mislabeling of Atlantic bluefin tuna. However, Japan has been fighting mislabeling using DNA testing since fiscal 2004.
In November 2005, a random DNA test conducted by the Fisheries Agency of Japan revealed that a report for 148 metric tons of tuna exported to Japan by a Chinese tuna longliner was falsified. The tuna, actually caught in the Atlantic, was labeled as originating from the Pacific, in an apparent bid to evade tighter regulations for Atlantic bigeye tuna. Japan urged China to investigate the case and take disciplinary action, and temporarily banned tuna imports from the vessel.
Separation between Atlantic bigeye and Indo-Pacific bigeye is based on DNA samples. There are two genotypes for Atlantic bigeye, while Indo-Pacific bigeye has only one, said Naozumi Miyabe, international research coordinator for tuna and tuna-like species at the Fisheries Research Agency’s National Research Institute of Far Seas Fisheries.
Even though different stocks of Atlantic bluefin tuna are the same species, the birthplace of the fish can be estimated from the existence of rare earth element isotopes. To discriminate between Atlantic bluefin tuna populations from eastern (Mediterranean Sea) and western (Gulf of Mexico) spawning areas, chemical signatures in the otoliths of yearlings from regional nurseries are used.
The otolith, part of the inner ear of finfish, can be examined using mass spectrometry to identify rare earth element isotopes peculiar to specific areas. The two Atlantic tuna populations mix significantly in the Atlantic but show high rates of returning to their respective spawning areas.
Miyabe said that among tuna exporting countries, New Zealand tests extensively, as the catch limits for the southern Pacific bluefin tuna are stricter than for the northern Pacific bluefin tuna that migrate into New Zealand waters.
Northern and southern bluefin tunas are physically similar and can easily be misidentified, posing problems in fishery management and marketing, so variation in mitochondrial DNA is used to distinguish between the two species. In Australia, the presence of northern bluefin tuna as far south as southwestern Tasmania has been confirmed using such tests.
A new test method reported in an October scientific paper co-authored by Dr. Jordi Viñas, a fish genetics specialist at Girona University in Spain and Dr. Sergi Tudela, head of fisheries at WWF Mediterranean, proposes a method for analysis of the DNA sequence variability of two unlinked genetic markets, a segment of the mitochondrial genome and a nuclear gene that enables full discrimination between all eight tuna species.
