Sea turtles experience considerable changes in water temperatures during migrations and seasonal movements that will influence their body temperatures. Nothing is known of how sea turtles’ core body temperatures vary from season to season at nesting sites. Over seven consecutive seasons we measured the surface temperatures of freshly laid eggs as proxies of core body temperatures of sea turtles using non-contact infrared thermometers. We estimated the temperatures of two species that have contrasting migration patterns - leatherbacks, which are adapted to migrate between tropical breeding sites to cold temperate waters, and hawksbills that are confined to the tropics and sub-tropics. We found considerable year-to-year variations in temperatures in both species (means ranging from 30.4°C to 31.5°C in leatherbacks), hawksbills the more so (28.1°C to 30.3°C). These differences will likely be modified by both natural seasonal variations and anthropogenic changes in global ocean temperatures and resulting changes in currents and water temperatures local to nesting beaches. These previously unrecognised fluctuations in body temperatures of nesting turtles have, it is argued, potential for predicting environmental tolerances, reproductive success, and nest site selection by sea turtles, and contribute to predictions of which rookeries may remain viable or not during future ocean warming.

Hand-held laser spot guided infrared thermometers. Satellite-based sea surface temperatures. Data processed and visualised using ORIGINlab and MS Excel software.