Outer Banks tuna study begins to yield results Electronic tags provide chronicle of fish's movements


PACIFIC GROVE, Calif. - Late last winter, in 8-foot seas 20 miles off Cape Hatteras, N.C., Dr. Barbara Block, a Stanford University marine biologist, and two teams of sometimes seasick researchers undertook a bold experiment. They spent five weeks wrestling more than 200 fish in the 300- to 500-pound class to the lurching decks of tiny charter fishing boats.

In rapid-fire movements carefully orchestrated to minimize the time the tuna were kept out of the water, they implanted two new types of computerized tags - 40 that pop up and disconnect from the fish after gathering data, and 160 that remain implanted and are removed only when the fish are caught. Then they released the fish.

Eight months later, the scientists were delighted with the results. Twelve of the pop-up tags were recovered within two weeks, by tracking the fish, just to make sure they were working. Over the summer, most of the other pop-up tags triggered their own timed release and started sending information to a satellite that was relayed to Block as e-mail. In recent weeks, two fishermen found and returned permanently implanted tags, which provided the researchers with the first moment-by-moment chronicle of six months in a bluefin tuna's travels.

'Icing on the cake'

"This is everything we dreamed about," said Block, who organized the multi-institutional research effort, financed by the Packard Foundation, the National Marine Fisheries Service, the MacArthur Foundation and the National Science Foundation. "This is the icing on the cake."

Dr. Eric Prince, chief of the migratory fishery biology division of the National Marine Fisheries Service in Miami and co-director of the two-year $550,000 project, said: "We're all extremely excited. When you know what the animal is doing every two minutes," information the internal tag provided, "nothing can compare with that."

Although scientists have suspected for years that giant bluefin tuna dive to great depths, Block was surprised to see how often the two recovered fish with internal tags dived deep, once to more than 2,400 feet, where the bluefin stayed for two hours. Researchers have also known that tuna are warmblooded, but information from the internal tags showed that the tuna maintained an internal body temperature of 80 degrees in the 40-degree waters the entire time at depth, offering evidence that warmbloodedness does not vary much as water temperature decreases.

The pop-up tags also revealed for the first time the initial migration paths of the bluefin as they fanned out across the western North Atlantic.

Tuna movements

"Some went north to the canyons off the East Coast, to Georges Banks and the Grand Banks," said Block, who in June 1996 received a five-year $245,000 MacArthur Foundation Fellowship for her molecular and behavioral research into giant bluefin. "Some went remarkably quickly to the Mid-Atlantic Ridge. In 90 days, several fish crossed into the eastern Atlantic."

Although the results are preliminary, the research may unravel the migration of the giant bluefin tuna and provide information needed to help save it from extinction. But the results also promise to cause controversy among the international fishing nations that vie for the giant bluefin, the most expensive fish in the world. In the raw fish market in Tokyo, the lust for the tuna's dark-red flesh can drive the price of a single fish up to $80,000.

As a result of the demand for bluefin tuna, the breeding stocks in the western Atlantic Ocean have been depleted by 80 percent to 90 percent over the last 22 years, to only 22,000 fish in 1991, according to a report by the International Commission for the Conservation of Atlantic Tunas, based in Madrid. The commission reported that the eastern Atlantic stocks in 1992 had dropped by half since 1970.

The fish is managed as two separate stocks. One stock, which is harvested mostly by European nations, is said to roam the eastern Atlantic and breed in the Mediterranean Sea. The other, which is said to breed in the Gulf of Mexico and roam the western Atlantic, is fished principally by the United States, Japan and Canada. An artificial boundary has been drawn down the middle of the Atlantic Ocean. And the European nations have far less stringent quotas than the nations that harvest tuna in the western Atlantic because stocks in the eastern Atlantic seem less endangered.

In 1995, the last year for which data are available, European nations caught 39,331 metric tons of giant bluefin tuna. During the same year, the United States, Japan and Canada, fishing under restrictions limiting them to about 2,500 metric tons, caught a combined 2,285 metric tons. That works out to only 24,000 fish.

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