Abstract
Nest relocation and shading are widely used conservation strategies intended to mitigate threats to marine turtle hatchling survival. However, these interventions may carry unintended fitness costs. Estimating such effects can be challenging, especially in the absence of opportunities to compare with natural, undisturbed nests. Green turtle ( Chelonia mydas ) clutches were assigned to one of three treatments ( in situ , shaded relocation, or unshaded relocation) on Heron Island, Queensland, Australia (23.44307° S, 151.91809° E), during two nesting seasons (Dec 2022 – Feb 2023 and Dec 2023 – Feb 2024). Incubation temperature, hatching and emergence success, sex ratio, morphology (carapace size and body mass), and performance (self-righting ability and crawl speed) were assessed. Relocated unshaded nests exhibited higher incubation temperatures than in situ and shaded nests, especially during the final two weeks of incubation. Consequently, warmer nests produced smaller hatchlings with higher mass relative to size (residual mass) and poorer self-righting performance. Notably, in situ and shaded relocated nests had comparable incubation temperatures, yet still differed in hatching success, hatchling size, and self-righting ability, indicating that relocation can carry developmental consequences independent of those related to thermal averages. These findings highlight the importance of prioritising in situ nesting where feasible and accounting for both thermal and non-thermal factors of relocation sites if relocation is required.