Grant: 19-026R
Project Title: Understanding the exposure of sea turtles to vessels: determining the potential impacts of vessel strike in South Florida
Project Manager: Dr. Mariana Fuentes and Dr. Elizabeth Bevan
Organization: Florida State University (Research and Educational Institute)
Grant Amount: $24,855.60
Completion Date: 2020-07-27

Summary: Vessel collision can kill or severely injure air-breathing marine fauna, and therefore poses a significant threat to marine animals, including sea turtles. The nearshore waters along the coast of Florida provide critical habitat for several species of sea turtles. As the number of vessels on the water increases, so does the potential for sea turtles to be struck by a boat, as evidence by an increase in the number of stranded sea turtles displaying signs of boat-related injuries. Developing and implementing strategies to reduce the impact of vessels on sea turtles is a high priority recovery action identified within federal Marine Turtle Recovery Plans. However, mitigation is challenging since broad scale restriction of boating activities can be economically and socially detrimental for local communities. Therefore, targeted mitigation measures are needed to effectively address this conservation concern. Such measures require detailed and location-specific information about the behavior and movement of turtles, as well as vessel activities, in areas where sea turtles are negatively impacted by vessels. The overlap from this information can provide insight on areas of high, medium, and low risk areas for vessel strikes, and thus help to focus management actions for optimum efficiency. This project will take place at the St. Lucie Inlet in south Florida, which is one area where the occurrence of sea turtle vessel strikes in Southern Florida is most common. This project will provide a framework that can be used in other areas of high vessel and sea turtle activity to devise management strategies for reducing the occurrence of vessel-related sea turtle injuries and mortality.

Results: Four field trips totaling 11 sampling days (12-15 July 2019, 26-28 October 2019, 17-20 January 2020, and 6-9 March 2020) were conducted as part of this project. During these trips, a total of 41 turtles were sighted (25 loggerheads – 10 adults, 8 subadults, and 7 underdetermined; 15 green turtles – 2 adults, 2 subadults, and 11 juveniles; and 1 Kemp’s ridley juvenile). With respect to vessels, 1479 vessels were sighted in the St. Lucie Inlet and nearby waterways – the majority being outboards (63.0%) followed by inboards (11.8%) and sailboats (11.7%). Turtles were most often sighted along the offshore reef system, particularly off Jupiter Island. Thirty-four of these sightings occurred in non-speed restricted areas compared to 5 sightings in “slow speed minimum wake” and 2 sightings in “25 MPH” channels – indicating that existing management zones do not cover a significant portion of turtle habitat use documented by this project. Vessel density was greatest inside the St. Lucie Inlet where the Indian River Lagoon, St. Lucie River, and Peck Lake all meet. This area represents a major intersection for vessels leaving or returning to dock, traveling to popular recreation destinations (such as a sand bar west of Sailfish Point just inside the Inlet), or heading to or returning from offshore locations. Under the existing management zones, this portion of the waterway is limited to 25 MPH. Unfortunately, this location is also the most common site of non-compliance with existing speed regulations. Despite the extensive boat traffic, sea turtles were documented in this area and are at risk for severe vessel interactions. Despite the lack of overlap between sea turtles and vessels in the St. Lucie Inlet and surrounding waterways observed by this project, the results do suggest additional lines of investigation that may be beneficial for management.