GALVESTON, Texas, Nov. 20 (UPI) -- The ear bone of the bluefin tuna might help researchers determine why numbers of the prized fish have been dwindling for the past 25 years, a Texas A&M University at Galveston scientist said Tuesday.
The bluefin is the largest and most-prized of all tuna types, weighing as much as 1,200 pounds and fetching as much as $50,000 on Asian markets.
"That's one big reason why its stock has decreased. It's probably been overfished," said Dr. Jay Rooker, an assistant professor of marine biology who has a multi-year grant from the National Marine Fisheries Service to study the bluefin.
The number of bluefins in the western Atlantic Ocean has dropped almost 90 percent since the 1970s, according to one study.
What Rooker's research team want to undercover is the "mixing" rate of bluefin tuna -- those that have spawned in one area and then travel 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, the dime-sized ear bone of the bluefin, takes on importance for the band of Texas A&M researchers. The bone adds an additional layer each year of the fish's life.
By distinguishing otoliths of the Mediterranean bluefin from those from the Gulf of Mexico, Rooker can determine several things, among them the age of the fish and its spawning grounds.
"The otolith provides age and growth information and tell us about the bluefin's environment," Rooker explained. "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 United States may be strongly influenced by fishing activities in the Mediterranean," he said. "What tuna fishermen in the United States 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."
