By Richard Gaines
Juvenile bluefin tuna, primarily 2- and 5-year-olds migrate along the Atlantic coast with core habitat from the Gulf of Maine and Cape Cod to Cape Hatteras as well as the offshore Gulf Stream, according to a tagging and tracking study of fish caught in 2005 and 2008 by the Large Pelagic Research Center in Gloucester.
"Our tagging results reveal annual dispersal patterns, behaviors and oceanographic associations of juveniles Atlantic bluefin tuna that were only surmised in earlier studies," wrote the authors Benjamin Galuardi and Molly Lutcavage, who is director of the center, a University of Massachusetts Amherst laboratory located at Hodgkins Cove in Gloucester's Bay View section.
Funded by National Oceanic and Atmospheric Administration, the peer-reviewed study was received in January, accepted in April and published last week.
"While adult bluefin tuna are exploited in the commercial fishery in the western Atlantic," Galuardi and Lutcavage wrote, "juveniles are highly sought by recreational anglers and constitutes a multi-million dollar sport fishery," much of it based here in Gloucester.
The vibrant commercial fishery for the giant bluefin has been captured for television viewers in the National Geographic channel's reality show, "Wicked Tuna," also based in Gloucester.
The global sushi market at times will pay tens of thousands of dollars for an especially fine, fatty fish which might weigh more than 500 pounds.
The recreational fishery takes "football" tuna, typically found in schools, that weigh one-tenth that size more or less. Tuna schools can often be seen just outside the Dog Bar breakwater.
The tagging study involved surgically implanting sensors, a procedure that "usually took less than 90 seconds to complete," in fish landed by boats from Gloucester, Chatham and Wachapreague, Va., and then freed, the authors explained.
Out of 58 fish given miniature pop-up satellite archival tags, 26 returned data, including external and internal temperature, light and pressure.
"Overall, core habitat utilization areas emerged southeast of Cape Cod, south of Long Island (N.Y.) and at the (Continental) shelf break from the Eastern Shore of Virginia to Cape Hatteras (off the Outer Banks of North Carolina)," the study found.
"Summer — July through September — distributions were more restricted to coastal areas; the Gulf Stream margin and (Continental) shelf break north of Cape Hatteras, extending to the southern Gulf of Maine.
"In autumn — October to December — a transitional period, core use areas shift southward," Galuardi and Lutcavage wrote. "By December, no tagged fish remained in the Gulf of Maine, and 50 percent utilization distributions were centered off the Eastern Shore of Virginia to Cape Hatteras.
'"Winter — January to March —spatial distributions were the largest in area and ranged farther south than in other seasons. In spring — April to June — tagged fish returned to areas north and west, constricting their overall range."
These juveniles showed a maximum recorded depth of 800 meters (a meter equals 1.09 yards) but "they spent the majority of their time in relatively shallow depth, less than 20 meters."
"The Gulf Stream emerged as an important juvenile habitat from autumn to spring," the study found.
Richard Gaines may be contacted at 978-283-7000 x3464 or firstname.lastname@example.org.
On the web
Find the bluefin study at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0037829