Tuna Tracking with Chemistry: A Test of the Two-Stock Hypothesis for Atlantic Bluefin Tuna

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The investigators hope to show that the otolith chemistry of bluefin tuna, specifically Sr/Ca and Ba/Ca measured at microscale resolution and with high analytical precision, will be a definitive signal in the recognition of trans-Atlantic migrations, stock mixing, and spawning habitats. The stock structure of Atlantic bluefin tuna (Thunnus thynnus) is currently one of the most controversial issues in fisheries management. The controversy centers on the management of Atlantic bluefin according to a two-stock model that assumes independent spawning grounds in the Mediterranean Sea and Gulf of Mexico. To date, there is no biological evidence to support this assumption. The investigators propose that the elemental chemistry of bluefin tuna otoliths can be analyzed to test the two-stock hypothesis and yield information about the spawning habits and habitats of individual fish. Microconstituent analysis of otoliths can be used to link individual fish to a particular hydrographic environment assuming that tracers are either incorporated into the otolith in proportion to their concentration in the surrounding seawater or by a temperature-dependent fractionation. Fish that aggregate for any length of time will share a multi-elemental fingerprint independent of genetic identity, which can be used to delineate stocks and determine population structure.