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Separate Eastern And Western Bluefin Stocks: Possibly An Illusion? Global, August 20, 12

New Jersey charter boat Capt. Mike Formichella, fishing about 30 miles offshore earlier this month, landed, tagged and released a baby bluefin tuna that had made the trans-Atlantic trip from the Bay of Biscay between France and Spain, a distance of roughly 2,000 miles, the Asbury Park Press reported.

The one-year-old weighed 30 pounds. “It’s pretty amazing,” Formicella was quoted as saying.

Molly Lutcavage, director of the Large Pelagics Research Center in Gloucester, said that while the age of the fish was surprising, the center’s tagging program has found a large cohort of bluefins born in the eastern Atlantic cross the ocean and mix with the western bluefins.

”The amount of mixing is as much as 50 percent to 75 percent,” Lutcavage told the Times in a telephone interview. “Bio-markers and chemical signals confirm the mixing is that extensive.

The growing body of evidence that the giant bluefins cross the ocean frequently and mix is important, Lutcavage explained, because the International Commission for the Conservation of Tunas — or ICCAT — assumes two separate stocks, eastern and western, for the purposes of regulatory conservation. The border line is 45 degrees west longitude, running from the southern tip of Greenland to a bit east of the mouth of the Amazon River in Brazil. Conservation efforts are better in the Western Atlantic, it is commonly accepted.

”U.S. boats fish within their quotas, but in the Mediterranean they are not doing as well,” she said.

While adherence to quotas is the norm in the Western Atlantic, the Mediterranean is another matter. For example, until his ouster last October, the family of the late Libyan dictator Moammar Gadhafi was heavily involved with bluefin tuna ranching and undoubtedly paid no heed to ICCAT quotas, according to Lutcavage and a number of journalists.

Most complaints about irresponsible human harvesting of bluefin focus in the eastern Atlantic and Mediterranean. In November 2010, when ICCAT met in Paris a team of reporters from the International Consortium of Investigative Journalist released a study that found “widespread illegalities rippling throughout the supply chain of the Mediterranean and East Atlantic bluefin tuna fishery and trade,” according to Sergi Tudela, of the World Wildlife Foundation Mediterranean.

Atlantic bluefin fishing is almost entirely limited to hook and harpoon — much of it based off Gloucester, as chronicled in the National Geographic channel reality show, “Wicked Tuna.”

Virtually everything about bluefin is hotly disputed including the status of the stocks. In May, the National Oceanic and Atmospheric Administration rejected a petition by Center for Biological Diversity to consider bluefin an “endangered species” which would have ended recreational and commercial fishing for bluefin in U.S. waters, without affecting tuna fishing elsewhere. However, NOAA did put bluefin on its watchlist pending a stock assessment to be done later this year.

”ICCAT established these (two) management areas based on two known separate bluefin spawning locations (the Mediterranean Sea and the Gulf of Mexico), and the assumptions that bluefin always return to their native nursery grounds ... that fish on each side mature at vastly different ages (3-5 years in the Mediterranean vs. 8-12 years in the Gulf of Mexico), and that the two stocks have very low rates of mixing,” the Large Pelagics Research Center notes on its website.

”Over the decades, tagging studies with simple ID tags have shown that young, immature bluefin leave their native feeding ground and cross the Atlantic to mix with juveniles on the other side, such as between the Bay of Biscay and the waters off Cape Cod or the mid-Atlantic states.

”More recent studies show that in some years, the percentage of young fish crossing the Atlantic from the east may range above 50 percent. Scientists are now using biological markers from fish tissues, including DNA, chemical isotope signatures, and pesticide levels, to discern where in the Atlantic a fish has resided. Despite the significant gains in understanding from new scientific approaches, many questions remain about migration paths, food habits, spawning locations, age at maturity, and population size and structure of Atlantic bluefin tuna. LPRC scientists and collaborators are conducting research focused on these gaps in understanding.”

The Large Pelagics Research Center, in partnership with the National Marine Fisheries Service and ICCAT, conducting an Atlantic-wide scientific conventional bluefin tagging program; under this program, ICCAT researchers aim to deploy 15,000 tags in the eastern Atlantic over three years and the Large Pelagics Research Center researchers aim to deploy 4,000 tags in the western Atlantic over two years. All tags are to be deployed on 1-3 year old bluefin.