Research Project: Origin of yellowfin tuna in the western Atlantic Ocean: importance of outside production to US fisheries
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Several novel tools are currently being used to investigate the natal origin and stock structure of Atlantic tunas, including natural chemical markers in hard parts (Rooker et al. 2008, 2014, 2019). Natural markers in otoliths (ear stones) show significant potential for determining origin and quantifying population connectivity. This is due to the fact that otoliths precipitate material (primarily calcium carbonate) as a fish grows, and the chemical composition of each newly accreted layer is often associated with physicochemical conditions of the water mass they inhabit. As a result, material deposited in the otolith during the first year of life serves as a natural marker of the individual’s nursery or place of origin. Previous studies have demonstrated that trace elements and stable isotopes in otoliths can be used to determine the origin of both temperate and tropical tunas (Wells et al. 2012, Kitchens et al. 2018, Rooker et al. 2019).
The goal of the SK-funded study was to determine the origin and migratory histories of yellowfin tuna from U.S. fisheries in the Atlantic: 1) Gulf of Mexico [GoM], 2) Mid Atlantic Bight [MAB], and 3) US territories in the Caribbean [CAR]. Our efforts centered on two questions: Q1) Are yellowfin tuna in U.S. fisheries derived from local production or from more distant production zones in the eastern Atlantic Ocean (EAO), and Q2) Are trans-Atlantic movements (E to W) common for yellowfin tuna caught in U.S. waters? Such questions are important to fishery managers because this species is currently managed as a single, panmictic stock, despite the fact that trans-Atlantic movement is well documented. Similar to previous studies, we used natural tracers in otoliths that are linked to ambient physicochemical conditions of the ocean to develop ‘birth certificates’ for individuals from different regions or nurseries in the Atlantic Ocean. Thus, the first step was to develop reliable baseline chemical signatures for young-of-the-year (YOY) tuna from all sources or production areas in the Atlantic Ocean. As demonstrated in Kitchens et al. (2018), classification success to regional nurseries is relatively high, supporting the use of these reference signatures to source yellowfin tuna to their place of origin.
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