The use of animal-borne devices (bio-loggers) has revolutionized the study of marine megafauna. However, bio-loggers can induce stress during deployment due to handling and adhesive application, whereas device retention may alter hydrodynamics, affecting agility, predator avoidance, and energy expenditure. It is therefore essential to assess the physiological and behavioral impacts of both attachment and retention. Here, we evaluated short-term effects of bio-loggers on sea turtles. (1) We measured how the exothermic reaction of epoxy resins used for attachment affects loggerhead (Caretta caretta) and hawksbill turtles (Eretmochelys imbricata) carapace temperature. Internal temperature increased by 1.6 to 6 °C, with hawksbills reporting higher values (+1.5°C). (2) We recorded heartbeat and breathing rates in loggerheads during attachment. (3) We assessed behavioral responses in loggerhead and green turtles (Chelonia mydas) in the Oceanogràfic of Valencia before, during, and after bio-logger deployment. Loggerheads showed a 28% increase in swimming activity with minimal scratching, suggesting stress from handling. Greens showed a 20.7% reduction in swimming, frequent scratching (8.2%) and attempts to dislocate the device with front flippers (1.3%), indicating stress from device retention. These species-specific responses highlight the importance of refining tagging protocols to minimize animal stress, ensure welfare and improve data reliability in conservation research.
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