Spatial mapping of vulnerability hotspots: Information for mitigating vessel-strike risks to sea turtles

Abstract

Mortality risk to imperiled animal populations from anthropogenic hazards can be managed by spatial limits on human behavior if exposure and vulnerability of the animals are known. To provide this information for sea turtles in waters near their nesting beaches, we mapped exposure to vessel strikes, which are a major, lethal hazard to these endangered animals. During the 2021 and 2022 nesting seasons, we carried out standardized transect line surveys off Florida’s Atlantic coast, focusing on Loggerhead and Green Sea Turtles. Using Distance Sampling and Density Surface Modeling, we estimated the distribution of turtles near the surface (thus vulnerable to vessel strikes) based on several covariates. Our results revealed a clustering of vulnerable turtles near the shore and within hotspots identified by adjacent nesting beach density over tens of kilometers. Contrary to risk assessments based on stranding data, our findings present a new perspective on potential strike risk. We propose that our methodology and data can significantly contribute to initiating human behavioral changes required to reduce widespread vessel strikes on sea turtles.

Keywords

• Density surface model
• Distance sampling
• Transects
• Vessel strike
• Nesting beach
• Slow zone