ESR prepress abstract  -  doi: 10.3354/esr00771

Density and exposure of surface-pelagic juvenile sea turtles to Deepwater Horizon oil

Trent L. McDonald*, Barbara A. Schroeder, Brian A. Stacy, Bryan Wallace, Leigh Ann Starcevich, Jonathan Gorham, Mandy C. Tumlin, Dave Cacela, Matthew Rissing, Danya B. McLamb, Eric Ruder, Blair E. Witherington

*Email: tmcdonald@west-inc.com

ABSTRACT: The 2010 Deepwater Horizon (DWH) oil spill posed a severe threat to surface-pelagic sea turtles because the surface convergence zones that provide vital habitat by aggregating pelagic Sargassum and other floating material, also aggregated floating oil. Following the DWH spill, turtle rescue operations between 17 May and 9 Sep 2010 documented 937 juvenile sea turtles in the spill area and examined 574 captured turtles. Of captured turtles, 81% were visibly oiled. Transect searches in convergence zones found Kemp’s ridleys (51% of individuals, 16.3 to 27.5 cm SCL), green turtles (37%, 15.8 to 31.7 cm SCL), loggerheads (7%, 6.5 to 21.2 cm SCL), hawksbills (2%, 14.4 to 21.5 cm SCL), and unidentified sea turtles (2%). Line-transect methods estimated the density of all surface-pelagic sea turtles in surface convergence zones to be 3.32 per km2 (95% CI = 2.82 to 3.88), and density of heavily oiled turtles to be 0.24 per km2 (95% CI = 0.15 to 0.39). Turtle densities and the areal extent of heavy oiling probability were used to estimate total number of turtles exposed to DWH oil. We estimate approximately 402000 surface-pelagic sea turtles were exposed, and of those, 54800 were likely to have been heavily oiled. Our estimates formed the basis of surface-pelagic juvenile sea turtle mortality estimates included in the DWH natural resource damage assessment.