Texas A&M University, USA
Jay Rooker is a Regents Professor and the McDaniel Chair of Marine Fisheries at Texas A&M University (TAMU). He arrived at TAMU in 1998 and holds faculty appointments in the Department of Marine Biology (Galveston) and Department of Wildlife & Fisheries Sciences (College Station). He received a PhD from the University of Texas at Austin and Post-doctoral training at the University of Maryland. He has been the Lead Scientist on a broad spectrum of projects on estuarine, coastal, and pelagic fishes over the past two decades.
Natural chemical markers in the otoliths of temperate and tropical tunas (Thunnus albacares, T. obesus, T. thynnus) were used to investigate their origin and spatial histories at the ocean-basin scale. Here, we provide an overview of the approach and general findings to date for studies conducted in both the Atlantic Ocean and Pacific Ocean. Characterizing the otolith chemistry of young-of-the-year (YOY) tunas is the first step in establishing chemical baselines for each putative nursery (i.e. source), and evaluating the suitability of the approach for investigating trans-ocean movement and homing capabilities. Spatial variation in otolith chemistry of YOY tunas was detected for all species examined and, although elemental ratios and stable isotopes both showed promise for determining an individual’s place of origin, classification success was typically higher for stable isotopes, particularly δ18O. The nursery origin of adolescent and adult T. albacares, T. obesus, and T. thynnus were determined by comparing their otolith core chemistry to YOY baselines, and several interesting patterns were detected. Trans-ocean or trans-boundary movements occurred for all three species examined, suggesting that these tunas are highly migratory with populations connected at the ocean-basin scale. Still, limited movements and high site fidelity were also observed, and this finding indicates that local (versus outside) production may be more important than previously assumed for certain populations of tunas. Given that yields and rebuilding plans are highly sensitive to the movement and mixing of individuals from different production zones, an improved understanding of connectivity is needed to ensure that tuna populations are sustainably managed.