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Decomposition of Kemp's ridley (Lepidochelys kempii) and green (Chelonia mydas) sea turtle carcasses and its application to backtrack modeling of beach strandings

Redwood W. Nero, Melissa Cook*, Jaymie L. Reneker, Zhankun Wang, Emma A. Schultz, Brian A. Stacy

*Corresponding author:

ABSTRACT: When a sea turtle dies, it typically sinks to the bottom, begins decomposing, and floats to the surface once sufficient internal gases have accumulated to produce positive buoyancy. This process is poorly characterized and is essential to understanding where and when sea turtles found on shore may have died. We conducted decomposition studies with detailed time-temperature histories using 37 cold-stunned sea turtle carcasses, 22 Kemp’s ridleys Lepidochelys kempii and 15 green sea turtles Chelonia mydas, at temperatures ranging from 14°C–32°C and depths of 2.2 to 9.5 m. There was strong depth/pressure related effect; carcasses took longer to float when incubated at greater depths than shallower depths at similar temperatures. Furthermore, time to float followed an inverse and non-linear relationship with ambient water temperature, with carcasses incubated at colder temperatures (~15°C) taking 8 times longer than those at 32°C at the same depth. We applied accumulated degree hours (ADH), the hourly sum of the ambient temperature a carcass experienced, to characterize the environmental conditions associated with different stages of decomposition and key events, including buoyancy and sinking. A formula for temperature-correction of ADH was calculated to fit a non-linear increase in decomposition at higher temperatures. These data were then used to improve an existing backtracking model by incorporating water temperature, depth (pressure), bathymetry, and postmortem condition. Heat maps of the probable mortality locations from the model agreed well with carcass and effigy drift experiments, demonstrating the overall reliability of the enhanced model. Our method can be used to estimate at-sea locations where sea turtles found washed ashore in northern Gulf of Mexico likely died and may help inform similar efforts in other regions.