Atlantic Bluefin Tuna Spawning Area Research

Scientists from NOAA’s National Marine Fisheries Service (NOAA Fisheries) and the University of Massachusetts Boston have found evidence of Atlantic bluefin tuna spawning activity off the northeastern United States in an area of open ocean south of New England and east of the Mid-Atlantic states called the Slope Sea.

The findings, published March 7 in the Proceedings of the National Academy of Sciences, suggest that the current life-history model for western Atlantic bluefin, which assumes spawning occurs only in the Gulf of Mexico, overestimates age-at-maturity. For that reason, the authors conclude that western Atlantic bluefin may be less vulnerable to fishing and other stressors than previously thought.

Prior to this research, the only known spawning grounds for Atlantic bluefin tuna were in the Gulf of Mexico and the Mediterranean Sea. The evidence for a new western Atlantic spawning ground came from a pair of Northeast Fisheries Science Center (NEFSC) research cruises in the Slope Sea during the summer of 2013.

“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,” said David Richardson of NOAA’s Northeast Fisheries Science Center (NEFSC), lead author of this study. “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.”

The research may help to resolve a longstanding debate in Atlantic bluefin tuna science. It had long been assumed that bluefin tuna start spawning at age 4 in the Mediterranean Sea and age 9 in the Gulf of Mexico.

Electronic tagging studies begun in the late 1990s revealed that many bluefin tuna, assumed to be of mature size, did not visit either spawning ground during the spawning season as expected.

This led some to propose that these larger fish were not spawning, and instead the age-at-maturity for western Atlantic bluefin tuna was 12-16 years, rather than 9 years, as was assumed in the stock assessment.

The scientific team for the study comprises researchers from NOAA’s Northeast Fisheries Science Center (NEFSC) and Alaska Fisheries Science Center (AFSC), the Large Pelagics Research Center at the University of Massachusetts Boston, the School of Marine Science and Technology at the University of Massachusetts Dartmouth, and NOAA’s Greater Atlantic Regional Fisheries Office (GARFO).

The new information will be considered along with other pertinent research as part of the regular ICCAT SCRS stock assessment process.

A single bluefin tuna can spawn millions of eggs, each of which is just over a millimeter in diameter, or the size of a poppy seed.

Atlantic bluefin tuna (Thunnus thynnus) is a high value species that ranges from the tropics to the sub-arctic, in coastal to international waters.

source: NOAA Fisheries