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Otolith Chemistry as a Natural Marker of Origin of Atlantic Bluefin Tuna Populations


Atlantic bluefin tuna (Thunnus thynnus) is a highly migratory species with a distribution that spans the north Atlantic basin.  Although bluefin tuna were initially considered to be of a single stock that spanned the entire North Atlantic, since the 1980s scientists and managers have recognized that there are two distinct spawning populations. The eastern population originates in the Mediterranean and the western population originates in the Gulf of Mexico.  A stock boundary divides east and west stocks at the meridian 45°W and the current management of Atlantic bluefin assumes no mixing occurs across this boundary. 

In recent decades, a suite of research methods have improved our understanding of Atlantic bluefin tuna movement. Stock identification methods (including genetics, otolith chemistry, conventional and electronic tagging) indicate that bluefin populations exhibit a high degree of mixing across the stock boundary, particularly during juvenile and sub-adult life stages. Characterizing stock composition and the effects of stock mixing is a key priority for improving assessment and management of Atlantic bluefin tuna. The aim of our research is to use otolith chemistry techniques to characterize the stock composition of bluefin tuna caught in the Gulf of Maine and integrate this information into the stock assessment and management process.

This project features a collaboration of experts on Atlantic bluefin tuna at multiple institutions. Samples of juvenile and adult bluefin otoliths have been provided by the commercial and recreation fisheries, creating a unique partnership between researchers and diverse components of the fishing industry.

Micromill used to sample otolith for chemical analysis (left), close up view of milling process (right).