Temperature-based modeling of incubation period to protect loggerhead hatchlings on an urban beach in Northwest Florida

Sea turtle hatchlings face many natural and anthropogenic threats during their short journey to the water after emerging from nests. Reducing hatchling mortality is critical to population recovery of imperiled sea turtle species; however, protecting hatchlings is particularly challenging on beaches degraded by human development and disturbances, including artificial lighting. Managers need practical methods to reduce hatchling mortality without harming their natural behavior or development. To address this need, we describe an approach to reduce mortality of loggerhead hatchlings that relies on prediction of clutch incubation length and knowledge of hatchling emergence patterns. We developed models to predict incubation length utilizing sand temperature and nest depth data from 133 loggerhead nests laid on an urban beach in Northwest Florida from 2013 to 2020. Incubation length was predicted to within 2.2 days using mean sand temperatures measured just outside of the clutch. Predicted accuracy improved to 1.9 days using a 2-parameter model incorporating sand temperature and measured depth to the topmost eggs. Hatchlings emerged almost exclusively at night in a single large group with no evidence of asynchronous emergences. Emergence times were skewed toward the early evening, in contrast to loggerhead nests on the Florida Atlantic coast which tend to hatch near midnight. Using these prediction tools, monitoring efforts could be focused on days and times of expected emergence to enable protection of hatchlings emerging naturally from nests left in situ. The method used here, while not a substitute for recovery of degraded nesting habitat, provides a way to protect hatchlings that avoids disturbing the eggs with instruments or restraining the hatchlings with cages or screens.