Grant: 23-015R
Project Title: Characterizing the Diet of Pier-Hooked Green Turtles
Project Manager: Cody Mott
Organization: Inwater Research Group (Non-Profit Organization)
Grant Amount: $9,800.00
Completion Date: 2026-02-11
Summary: Green turtles (Chelonia mydas) are generally thought to be herbivorous as juveniles, but recent work indicates that in many situations these turtles maintain an omnivorous diet. In Florida, sea turtle stranding records indicate that some green turtles forage on fishing bait and fishing discards based on the presence of ingested tackle. While green turtles are the most common sea turtle species documented with fishing interactions in the state, no research has attempted to examine this behavior or the importance of fishing bait to their diet. The goal of this study is to characterize and quantify green turtle interactions with a fishing pier in Florida. Specifically, we will study how proximity to a fishing pier affects green turtle diet by comparing pier-hooked turtles to turtles captured on the adjacent reef, and at a control site without a nearby pier. Turtle diet preference will be assessed using esophageal lavage, blood analytes, and stable isotope analysis. This will also quantify the proportion of fishing bait ingested by turtles and determine the relative importance of animal protein in the diets of study animals. As green turtle abundance increases in coastal waters, anthropogenic threats including climate change and habitat loss will escalate competition for resources. Additional competition is expected to increase the frequency of green turtles seeking resources at fishing piers, which may lead to further hooking and entanglement injuries. This study will collect baseline data on the diet and behavior of juvenile green turtles that interact with a recreational fishing pier. It will assist conservation and pier managers aiming to minimize future interactions between recreational fishermen and this protected species. The proposed methods can be applied to additional piers and recreational fishing sites to better understand this anthropogenic threat more broadly.
Results: This project, including sample analysis and interpretation, was completed in December 2025. The results are part of the first two chapters of Mr. Mott's doctoral dissertation. A draft of the dissertation is included, with the final version expected in May 2026. The study examined whether nitrogenous compounds in the blood of juvenile green turtle (total protein, blood urea nitrogen (BUN), and uric acid) could be used to infer dietary patterns at three sites with differing levels of fishing pressure. Turtles were sampled at a recreational fishing pier (n = 39), an adjacent reef (n = 29), and a control site at a power plant with minimal fishing pressure (n = 33). Individual turtles were captured and resampled multiple times during the study (range: 1-5 captures). In total, 67 individual turtles were sampled, including five turtles captured at both the pier and reef locations. No turtles from the power plant were captured at other study sites. Total protein concentrations increased with turtle size but did not vary by capture location or pier interaction, indicating that total protein was not a reliable predictor of dietary protein intake.