Small bone could solve bluefin mystery

November 08, 2001

COLLEGE STATION, November 8 - As Exhibit A, the ear bone of a tuna is hardly courtroom evidence that could solve a mystery. But in true Colombo style, this tiny piece of the fish's skeleton could be the big answer to a marine riddle.

Texas A&M University at Galveston researchers are studying the otolith - the ear bone about the size of a dime in the bluefin tuna - to see why the numbers of the great fish have been dwindling for the past 25 years.

If you think the bluefin is just another tuna, think again.

It is the largest and most-prized of all tuna types, weighing as much as 1,200 pounds. One bluefin can fetch as much as $50,000 on Asian markets, where its meat is a precious commodity. It's not the type of tuna that ends up on a sandwich - that distinction belongs to other tuna.

"That's one big reason why its stock has decreased. It's probably been overfished," says Dr. Jay Rooker, assistant professor of marine biology who has a multi-year grant from the National Marine Fisheries Service to study the bluefin's habits.

One study shows the number of bluefins in the western Atlantic Ocean has dropped almost 90 percent since the 1970s.

Rooker says what he and his research team want to undercover is the "mixing" rate of bluefin tuna - those that have spawned in one area and then travel great distances, sometimes thousands of miles.

Some bluefin spawn in the Gulf of Mexico and travel as far as the Italian coast, while in the Pacific it is not uncommon for bluefin to spawn near Japan and be found near Mexico.

That's where the otolith comes in.

The piece of bone adds an additional layer each year of the bluefin's life. Distinguishing the otoliths of the Mediterranean bluefin from those from the Gulf of Mexico will tell Rooker several things, among them the age of the fish and its nursery areas.

"The otolith provides age and growth information and will tell us about the bluefin's environment," Rooker explains. "We can learn a lot about the entire fish and its habits from this one piece of small bone."

The mixing rates of the bluefin will tell researchers more about its future.

"If there is a 10 or 20 percent mixing rate of the Gulf bluefin and the Mediterranean bluefin, stocks present off the U.S. may be strongly influenced by fishing activities in the Mediterranean," he adds. "What tuna fishermen in the U.S. seem to think is that the bluefin is being highly overfished in the Mediterranean, and this study should give us some answers.

"If the mixing rate is high, it will help us determine how we can manage the stock of bluefins in the future."
Contact: Keith Randall, (979) 845-4644,

Texas A&M University

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