Bidirectional migration routes of Chelonia mydas from the northern Great Barrier Reef

Understanding the full migration dynamics of highly migratory marine species is essential for effective conservation and management. In sea turtles, research has largely focused on one-way, post-nesting migrations, leaving key gaps in knowledge regarding return movements and overall route fidelity. This study investigated the route fidelity of Northern Great Barrier Reef (nGBR) green turtles (Chelonia mydas) by comparing outward migrations from foraging grounds to nesting sites with return migrations to foraging areas. Satellite tracking data from eight individuals were analysed using ArcGIS to map migration routes, with comparisons made based on migration distance, duration, and speed. Route overlap between outward and return journeys was quantified using a 5 km pairwise buffer analysis. Outward migrations to nesting beaches (mean: 372 ± 136 km) were significantly longer than return migrations (mean: 252 ± 28 km) (P < 0.05). Route overlap was low, ranging from 2 to 17%, indicating limited reuse of migration pathways. These findings demonstrate that in our study nGBR green turtles do not consistently use the same routes between foraging and nesting sites, suggesting more complex spatial behaviour than previously recognised. As conservation strategies increasingly emphasise the protection of migratory corridors, these results highlight the importance of accounting for variability in movement patterns and the potential for exposure to spatially diverse anthropogenic threats.