Foraging Habits of Green Sea Turtles (Chelonia mydas) in the Northwestern Gulf of Mexico

Lyndsey N Howell,Donna J Shaver

doi:10.3389/fmars.2021.658368

Abstract

Knowledge of green turtle (Chelonia mydas) foraging ecology in the northwestern Gulf of Mexico (GOM) is critical as populations begin to recover from heavy harvesting in prior centuries. We present a comprehensive long-term assessment of green turtle diets from carcasses salvaged from 1987 to 2014 along the Texas coast. Digestive tract contents were examined from 420 green turtles, ranging in size from 7.3 to 86.0 cm in straight carapace length (SCLmax). Green turtles as small as 16.2 cm SCLmaxrecruit from the oceanic environment to nearshore foraging habitat in the northwestern GOM and consume macroalgae principally. A successive shift in diet and habitat to inshore seagrasses was evident by the seagrass-dominated diet of turtles larger than 30 cm SCLmax. Animal matter remained a frequently ingested diet item suggesting these immature green turtles are better classified as omnivores. The overall evidence indicates that Texas’ recovering green turtle assemblage is exhibiting foraging plasticity within seagrass meadows changing species composition and density.

Highlights

Green turtles (Chelonia mydas) were once so abundant in Texas waters that they supported a commercial fishery, with a peak annual landing of approximately 265,350 kg of turtles in 1890 (Hildebrand, 1982)
We characterized the diet of green turtles stranding along the Texas coast for 28 years to evaluate changes over time
This first long-term diet study of Texas green turtles demonstrated turtles ingest a diversity of food items across size classes with foraging differences observed seasonally and temporally

Summary

Introduction

Green turtles (Chelonia mydas) were once so abundant in Texas waters that they supported a commercial fishery, with a peak annual landing of approximately 265,350 kg of turtles in 1890 (Hildebrand, 1982). Pressures on this marine turtle assemblage were inexorable. By 1903 the green turtle fishery had virtually collapsed due to the commercial harvest and severe hypothermic stunning events in the winters of 1894–1895 and 1899, which decimated the turtle population (Hildebrand, 1982; Doughty, 1984). From 1980 through 2015, the largest totals (>450 turtles) of turtles cold-stunned were during the winters of 2009–2010, 2010–2011, 2013–2014, and 2014–2015 (Shaver et al, 2017)

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Conclusion