The Atlantic bluefin tuna is generally known to spawn in the Gulf of Mexico and the Mediterranean Sea. Until a recent study, this Atlantic fish was thought to spawn in only those two locations.
But, that may have changed with a big discovery. New evidence shows that these tuna are spawning in the Slope Sea, an area of open ocean south of New England and east of the Mid-Atlantic states along the East Coast of the U.S. This information was found by researchers from NOAA's National Marine Fisheries Service and the University of Massachusetts-Boston.
The new findings show the likelihood that western Atlantic bluefins are less threatened by fishing and other stresses than previously believed. The idea is that the life-history model for western Atlantic bluefins that is currently in play, the one based on spawning in the Gulf of Mexico, has an inaccurate assumption (which is too high) of the fish's age at maturity.
This evidence is from Northeast Fisheries Science Center's (NEFSC) research cruises in the summer of 2013 in the Slope Sea.
"We collected 67 larval bluefin tuna during these two cruises, and the catch rates were comparable to the number collected during the annual bluefin tuna larval survey in the Gulf of Mexico," David Richardson of NEFSC and study lead author, said. "Most of these larvae were small, less than 5 millimeters, and were estimated to be less than one week old. Drifting buoy data confirmed that these small larvae could not possibly have been transported into this area from the Gulf of Mexico spawning ground."
It's important to know about these fish, Thunnus thynnus, because they are known as a high-value species and they are physically able to range from the tropics to the sub-arctic, in waters near shore and very far into the ocean. They were globally overfished for many years, but international cooperation has resulted in increased abundance of both eastern and western Atlantic bluefins.
Earlier studies noting that some fish weren't spawning in either the Gulf of Mexico or the Mediterranean led some researchers to believe that larger fish among the western Atlantic bluefins were not spawning, and that the age-at-maturity for them was 12-16 years, not nine years, as had been assumed previously.
Molly Lutcavage of the University of Massachusetts-Boston, a study co-author, believed instead that the fish that did not spawn in those two places might be spawning elsewhere. Electronic tagging has shown a different story.
"Last year, we demonstrated using endocrine measurements that bluefin tuna in the western Atlantic mature at around 5 years of age. That study, and ones before it, predicted that these smaller fish would spawn in a more northerly area closer to the summertime foraging grounds in the Gulf of Maine and Canadian waters," Lutcavage said. "The evidence of spawning in the Slope Sea, and the analysis of the tagging data, suggests that western Atlantic bluefin tuna are partitioning spawning areas by size, and that a younger age at maturity should be used in the stock assessment."
The findings were published in the Proceedings of the National Academy of Sciences.
Follow Catherine Arnold on Twitter at @TreesWhales.
