Determining Soil Temperature Differences on the Beaches of Bald Head Island with Relation to Sea Turtle Gender

The gender of sea turtles is determined by the temperature of the sand that turtle eggs are exposed to during their incubation period. Warmer sand temperatures yield female sea turtle hatchlings, while cooler temperatures yield males. Hatchlings with incubation temperatures in between these thresholds will be a mix of females and males, with a higher probability of females on the warmer side of the scale.

In North Carolina, the beaches of Bald Head Island (BHI) are a primary nesting ground for sea turtles each year. Over the past three years, an average of 5,600 sea turtle hatchlings per year reached the sea from BHI. Understanding the overall weather conditions along the shores of BHI is valuable in determining potential changes in sea turtle gender. In cooperation with the BHI Conservancy, the North Carolina State Climate Office (NCSCO) is piloting a study to explore sand temperature during nesting season with respect to the probability of sea turtle hatchling gender. Five sand temperature monitoring stations are in operation on the island for the 2019 nesting season – two on South Beach, two on East Beach, and one on West Beach. Each station is equipped with two Campbell Scientific 109 soil temperature sensors – a shallow sensor at 20-30cm below ground, and a deep sensor at 60-70cm below ground – to reflect the range in depth of natural turtle nests in the area. Station locations are strategically chosen in order to collect data from multiple sides of the island so that island orientation and sand texture are also considered. Monitoring the spatial variation of sand temperature on BHI provides the opportunity to predict the gender probability of hatchlings on the island’s beaches over the course of the study.

Results of the pilot study will be presented, along with probability estimations of sea turtle hatchling gender based on literature-suggested temperature thresholds. The collected sand temperature data will provide a reference point for any future studies to determine changes in sand temperature over time. Increments of just a few degrees could drastically tip the scales of sea turtle gender determination.