High site fidelity, slow growth, and compromised physiological condition in the Rapa Nui green turtle aggregation

Despite the ecological and cultural importance of green turtles Chelonia mydas across Oceania, knowledge of their demography, population trends, physiological condition, and anthropogenic pressures at foraging habitats remains limited. Rapa Nui (Easter Island), located at the eastern edge of the Polynesian Triangle, represents a key biogeographical link connecting South American and Polynesian green turtle populations. Here, we evaluated the demographic structure, residency patterns, somatic growth, body condition, and physiological status of green turtles inhabiting Rapa Nui during surveys conducted in 2018, 2023, and 2024. Using photo-identification, morphometric measurements, and hematological and biochemical analyses, we provide an integrated assessment of this isolated neritic aggregation. The aggregation was dominated by juvenile yellow-morphotype turtles, which exhibited exceptionally high site fidelity, unusually slow somatic growth, and relatively high body condition compared with turtles from other foraging aggregations across Oceania. Significant interannual variation was detected in multiple hematological and biochemical parameters, yet recurrent physiological alterations, including disrupted erythropoiesis, leukocyte imbalance, and biochemical evidence of subclinical hepatic and renal dysfunction, persisted across sampling periods, indicating a persistent pattern of compromised physiological condition. Together with previous clinical and toxicological evidence, these findings suggest that resident turtles are exposed to persistent local environmental and anthropogenic stressors. Our results identify Rapa Nui as a biologically important foraging ground supporting a physiologically compromised green turtle aggregation and emphasize the need for integrated conservation strategies that combine physiological, demographic, and ecological information to safeguard a species of profound cultural and spiritual importance to many Pacific Island communities.