Comparing environmental characteristics of larval bluefin tuna (Thunnus thynnus) habitat in the Gulf of Mexico and western Mediterranean Sea

Atlantic bluefin tuna undertake long migrations to reach warm, low productivity spawning grounds in the Gulf of Mexico and Mediterranean Sea. Peak spawning occurs during spring in the Gulf of Mexico, and summer in the Mediterranean. Environmental conditions within spawning areas appear unfavorable for adult feeding and physiology, and so have been presumed to benefit larval survival, through enhanced feeding conditions, larval retention or growth rates. In this study, a comparison of the environmental characteristics of both spawning sites was completed using standardized environmental data and modeling methods. Artificial neural network predictive models of larval occurrence were constructed using historical larval collections, and environmental variables from both in situ and remotely sensed sources. Results showed that larvae on both spawning grounds were most likely to be found in warm (23-28°C), low chlorophyll waters with moderate current velocities, and favorable regional retention conditions. In the Gulf of Mexico, larvae were located in offshore waters outside of the Loop Current and warm eddies, while in the western Mediterranean, larval occurrences were associated with the confluence of inflowing Atlantic waters and saltier resident surface waters. Results suggested common themes within preferred spawning grounds on both sides of the Atlantic Ocean. However, the ecological processes governing larval survival and eventual recruitment are yet to be fully understoo