Environmental preferences and jurisdictional distribution of juvenile loggerheads in the eastern North Pacific

Abstract While the basin-scale movements of North Pacific loggerheads are well documented, habitat use remains poorly understood for juveniles in the eastern North Pacific (ENP), including the exclusive economic zones (EEZs) of Mexico and the United States (U.S.). These areas represent developmental habitats where turtles encounter dynamic environmental conditions, fisheries threats, and management frameworks. Here, we used satellite telemetry data from 53 juvenile loggerheads (2023–2025) to characterize seasonal environmental preferences using sea surface temperature (SST) and chlorophyll-a (chl-a). Juveniles occupied waters with a mean SST of 17.4 °C (10–90th percentile: 15.4–19.9 °C) and mean chl-a concentrations of 0.14 mg/m 3 (10–90th percentile: 0.07–0.22 mg/m 3 ). These thresholds were applied to 2014–2025 oceanographic data, representing warm ocean conditions in the ENP, to summarize inferred seasonal patterns of suitable loggerhead habitat across jurisdictions. Suitable habitat shifted seasonally, with 2–31% of the U.S. EEZ and 1–13% of the Mexican EEZ containing suitable habitat annually. Overall, 86% of habitat occurred in areas beyond national jurisdiction, compared to 6% within the U.S. EEZ and 8% in the Mexican EEZ. These findings highlight the transboundary nature of juvenile loggerhead habitat in the ENP and the importance of high seas frameworks for conserving this endangered population in a changing ocean.