The authors of this article used acoustic telemetry to track the migrations of 72 royal drams (Sparus aurata) for more than two years, between a coastal lagoon and the sea in the western Mediterranean, and related these movements to the dominant environmental parameters. They then captured sea bream in coastal lagoons and used implanted data storage beacons to study the cardiac responses of animals swimming in freedom in the face of sudden changes in temperature. This has allowed an innovative interpretation of seasonal migration patterns for spawning, as well as apparent migrations to shelters in summer, with regard to cardiac tolerance thresholds to warming or cooling. Telemetry data indicated that the temperature of the lagoon was the main trigger for seasonal departures to the sea in the fall and returns to the lagoon in the spring for food. Cardiac responses to cooling showed that the temperature of 13°C constituted a lower subletal threshold, and the sea sea bream did not return to the lagoon until the average water temperature reached 14.4°C. Cardiac responses to warming showed that 29°C corresponded to a higher subletal threshold, and in summer, sea sea sea bream made apparent refuge migrations when the lagoon temperature rose rapidly to exceed an average of 27.4°C.
This study shows that the combination of acoustic telemetry and ecophysiology can provide information on the mechanisms underlying the migratory movements of large fish species, providing a better understanding of the impact that ongoing climate change will have on them.
