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Holy mackerel: A breakthrough in tuna science?

Can Japanese scientists save a species, and that tasty sashimi on your plate?

A Japanese fisherman delivers tuna to an auction at the Katsuura Fishing Port in Nachi-Katsuura Town, central Japan June 5, 2008. The Katsuura Fishing Port, one of Japan's prominent ports, is known for the largest catch of fresh tuna in Japan. Japan's high consumption of bluefin tuna is blamed for reducing stocks of the fish, but Japanese scientists are working on ways to increase stocks of bluefin tuna. (Issei Kato/Reuters)

TOKYO — The next time you dine at a Japanese restaurant, try to steer clear of the tuna sashimi. If you're unable to resist the temptation  — and, let's face it how many of us can? — make sure you savor every last slice. In just a few years, it may have disappeared from the menu for good.

Our appetite for the undisputed “king of sushi,” whose succulent flesh is prized by diners at high-class restaurants from Tokyo to London and New York, is far from being sated.

Only last week the conservation group WWF warned that Mediterranean bluefin tuna stocks were on the verge of collapse, and the breeding population just three years from extinction, as a result of overfishing and a failure to curb our desire for melt-in-the mouth otoro.

Demand in Japan, and increasingly the U.S., Europe and China, is decimating stocks among the world’s four bluefin populations. The number of Mediterranean bluefin, for example, has more than halved since the 1950s.

Attempts at imposing ambitious quotas have had little impact. Although fisheries from several countries agreed on new bluefin quotas late last year, they were still some 47 percent higher than the levels recommended by their own scientists — a political fudge that environmental groups condemned as a “disgrace.”

While Japan is often cast as the villain of the piece for its voracious consumption of bluefin, it may also offer the key to the species’ survival, thanks to a team of researchers working out of a laboratory in Tokyo.

The team’s leader, Goro Yoshizaki, a professor at Tokyo University of Marine Science and Technology, has perfected a method of assisted reproduction in which sperm and ovaries from donor trout are implanted in salmon recipients. When the salmon reach maturity and mate, they produce a large number of hybrids, but also a smaller number of pure trout.

Last year his work reached a critical point when he identified the presence of sperm of a nibe croaker in the testes of a mackerel, saltwater fish that have physiological similarities to tuna.

Now Yoshizaki is in a race against time to save the imperiled bluefin.