Grant: 18-010R
Project Title: Characterization Of Marine Turtles On Nearshore Reefs Heavily Impacted By Humans
Project Manager: Cody R. Mott
Organization: Inwater Research Group (Non-Profit Organization)
Grant Amount: $7,125.00
Completion Date: 2020-11-30
Summary: Inwater Research Group (IRG) will conduct a study of sea turtles along south Florida nearshore reef. Marine turtles have been consistently documented on the shallow nearshore reefs off of Boca Raton and Deerfield Beach, Florida. The reef is easily accessible, has consistently good environmental conditions, and can be surveyed in a single day making it an optimal study location. However, there has not been any effort to systematically quantify the demographics of turtles utilizing the reef in more than 25 years. Additionally, an inlet and pier adjacent to the reef provide an opportunity to better understand how these structures impact turtles inhabiting nearshore reefs. IRG will collect basic demographic and dietary data to thoroughly characterize the local aggregation of sea turtles and acoustically tag a subset of reef captured turtles to track their movements. Separately, Gumbo Limbo Research and Rehabilitation team will collect the same demographic and dietary data from turtles hooked at the Deerfield Beach fishing pier located within the study site. They will also acoustically tag a subset of pier hooked turtles and track their movements. Data from reef captured and pier hooked turtles will then be compared. The goal is to understand if pier hooked turtles solely forage near the pier or are part of the larger group of turtles inhabiting the entire reef tract. This study gives IRG the opportunity to efficiently document the turtles residing on nearshore reefs and through collaboration with another organization, collect additional information on how human activities may impact turtles within the study area.
Results: The preliminary data collected as part of this project strongly suggests that there are measurable differences between juvenile green turtles hooked at the Deerfield Pier and those captured along the adjacent reef tract (500 – 1,000 m from the pier). Acoustic tagging data indicates turtles have a strong affinity to their capture/hooking location. However, tracking of fine-scale movements in the future may lead to more robust determinations of habitat use and home range size. Stable isotope analysis was particularly informative and showed highly significant difference in foraging between the two groups of turtles. Elevated ?15N nitrogen values for pier hooked turtles, suggest that turtles are selecting fish over other food available food items. A subset of juvenile green turtles inhabiting the nearshore reef show an affinity for the pier located within the study area. While individuals may benefit from higher protein / caloric intake associated with fishing bait and discards, the risk of injury due to hooking may also increase. This hypothesis should be further examined but may represent an example of ecological trap and have consequences for the persistence of this green turtle aggregation. We plan to continue this study and focus on differences in movement, diet, and risks from recreational fishing encounters between reef captured and pier hooked turtles.