[PAST EVENT] Transatlantic Movements of Juvenile Bluefin Tuna Inferred from Analyses of Organochlorine Tracers

September 30, 2015
12pm - 1pm
VIMS - Watermen's Hall, Classroom A/B
1375 Greate Road
Gloucester Point, VA 23062Map this location
Fisheries Science Noon Seminar Series

Speaker: Dr. John Graves, VIMS

Title: Transatlantic Movements of Juvenile Atlantic Bluefin Tuna Inferred from Analyses of Organochlorine Tracers

Atlantic bluefin tuna (Thunnus thynnus) are believed to comprise an eastern Atlantic stock that spawns in the Mediterranean Sea and a western Atlantic stock that spawns in the Gulf of Mexico, with considerable admixture of the two stocks throughout the Atlantic. Understanding the timing and magnitude of mixing of the two stocks is essential for accurate stock assessments. Ratios of organochlorine pollutants are significantly different between the eastern and western Atlantic and can be used to infer recent transatlantic movements of bluefin tuna. In this study we observed limited variation of organochlorine pollutant ratios across collections of young-of-the-year (YOY) bluefin tuna from the western North Atlantic (WNA) and eastern North Atlantic (ENA) in different years, and highly significant differences between WNA and ENA YOY samples each year and for all years combined. A significant increase in organochlorine ratios was noted between YOY and age-1 ENA bluefin tuna, consistent with the movement of YOY out of the Mediterranean Sea and into the ENA. Using baseline organochlorine ratios from WNA YOY to identify recent eastern migrants, 29% of age-2, 33% of age-3, and 24% of age-4 juvenile bluefin tuna in the WNA were identified as recent migrants from the east during 2011 and 2012. Applying baseline ratios from age-1 ENA bluefin tuna to identify recent migrants from the WNA, 14.3% of age-2, 9.5% of age-3, and 0% of age-4 juvenile bluefin tuna caught in the Bay of Biscay fishery were identified as recent western migrants during 2010 and 2011. These data reveal substantial connectivity of juvenile bluefin tuna across the North Atlantic, and demonstrate that WNA juveniles are heavily subsidized by eastern fish.

[[v|mfabrizio,Professor Mary Fabrizio]]