ESR 33:39-50 (2017)  -  DOI: https://doi.org/10.3354/esr00758

Toxicological estimation of mortality of oceanic sea turtles oiled during the Deepwater Horizon oil spill

C. L. Mitchelmore1,*, C. A. Bishop2, T. K. Collier3

1Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, 146 Williams Street, Solomons, MD 20688, USA
2657 202nd Street, Langley, British Columbia V2Z 1V7, Canada
3Joint Office for Science Support, University Corporation for Atmospheric Research, 3300 Mitchell Lane, Boulder, CO 80301, USA
*Corresponding author:

ABSTRACT: Using multiple lines of evidence, we estimated the mortality of oceanic sea turtles that were minimally to moderately oiled by the 2010 BP Deepwater Horizon (DWH) oil spill in the Gulf of Mexico. Using estimates of the oil ingested by oceanic sea turtles and comparing them to toxic endpoints following oil ingestion in turtles and other vertebrate species, we derived an estimated percentage of mortality for oil-exposed oceanic sea turtles. Oil ingestion (mg kg-1 BW d-1) in oceanic sea turtles was estimated based on extent of oiling categories assigned by a sea turtle technical working group (STTWG) as follows: non-oiled (0), minimally oiled (1), lightly oiled (2), moderately oiled (3) and heavily oiled (4). Because the STTWG concluded that 100% of heavily oiled turtles would have died from the physical effects of heavy oiling, we limited our assessment of mortality to turtles in categories 0 to 3 and estimated how many of these turtles would have died from ingestion of oil. The estimated mortality was 85% for category 3, 50% for category 2 and 25% for category 1. Visibly non-oiled turtles (category 0) were assigned 0% mortality. To calculate the overall mortality for all turtles, the mortality estimations for categories 0 to 3 were applied to the numbers of turtles observed with different degrees of oiling, as documented by direct capture operations during the DWH spill. We concluded that, overall, approximately 30% of all oceanic turtles in the region affected by the DWH spill that were not heavily oiled would have died from ingestion of oil.


KEY WORDS: Toxicology · Mortality · Oceanic sea turtles · Deepwater Horizon · Oil spill · NRDA


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Cite this article as: Mitchelmore CL, Bishop CA, Collier TK (2017) Toxicological estimation of mortality of oceanic sea turtles oiled during the Deepwater Horizon oil spill. Endang Species Res 33:39-50. https://doi.org/10.3354/esr00758

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