Herpetological Conservation and Biology 13(1):224–239. Submitted: 10 April 2017; Accepted: 16 March 2018; Published 30 April 2018. SEA TURTLE ABUNDANCE AND DEMOGRAPHIC MEASUREMENTS IN A MARINE PROTECTED AREA IN THE FLORIDA KEYS, USA RICHARD M. HERREN1,2,4, DEAN A. BAGLEY1, MICHAEL J. BRESETTE1, KAREN G. HOLLOWAY-ADKINS3, DAVE CLARK1, AND BLAIR E. WITHERINGTON1 1Inwater Research Group, Inc., 4160 NE Hyline Drive, Jensen Beach, Florida 34957, USA 2Department of Wildlife Ecology and Conservation, University of Florida, 110 Newins-Ziegler Hall, Gainesville, Florida, 32611, USA 3East Coast Biologists, Inc., 141 Atlantic Avenue, Indialantic, Florida 32903, USA 4Corresponding author, e-mail:
[email protected] Abstract.—We used vessel-based surveys to estimate sea turtle abundance and capture them in a 129 km2 area within the Key West National Wildlife Refuge, USA, and adjacent waters. We measured captured turtles, externally examined them for disease and injuries, and analyzed diet in 62 Green Turtles (Chelonia mydas). Between 2003– 2012, we sighted 1,087 Green Turtles, 789 Loggerheads (Caretta caretta), 65 Hawksbills (Eretmochelys imbricata), one Kemp’s Ridley (Lepidochelys kempii), and 12 unidentified turtles. We fitted the sighting data to a probability of detection model, which gave us an estimate of 46.4 turtles km-2. Most sightings were clustered in four distinct areas that were in the lee of islands. Captured Loggerheads were significantly larger (mean straight carapace length [SCL ± SD], 74.2 ± 9.3 cm) than Green Turtles (54.3 ± 21.8 cm) which were significantly larger than Hawksbills (46.7 ± 11.3 cm). However, Green Turtles were a mixture of three size classes and exhibited significant size class partitioning with larger turtles found in deeper water (> 3 m) and smaller turtles found in shallower water (< 3 m).