δ13C and δ15N in the endangered Kemp’s ridley sea turtle Lepidochelys kempii after the Deepwater Horizon oil spill

The Deepwater Horizon explosion in April 2010 and subsequent oil spill released 3.19 x 10(6) barrels (5.07 x 10(8) 1) of MC252 crude oil into important foraging areas of the endangered Kemp's ridley sea turtle Lepidochelys kempii (Lk) in the northern Gulf of Mexico (GoM). We measured delta C-13 and delta N-15 in scute biopsy samples from 33 Lk nesting in Texas during the period 2010 to 2012. Of these, 27 were equipped with satellite transmitters and were tracked to traditional foraging areas in the northern GoM after the spill. Differences in delta C-13 between the oldest and newest scute layers from 2010 nesters were not significant, but delta C-13 in the newest layers from 2011 and 2012 nesters was significantly lower compared to 2010. delta N-15 differences were not statistically significant. Collectively, the stable isotope and tracking data indicate that the lower delta C-13 values reflect the incorporation of oil rather than changes in diet or foraging area. Discriminant analysis indicated that 51.5% of the turtles sampled had isotope signatures indicating oil exposure. Growth of the Lk population slowed in the years following the spill. The involvement of oil exposure in recent population trends is unknown, but long-term effects may not be evident for many years. Our results indicate that C isotope signatures in scutes may be useful biomarkers of sea turtle exposure to oil.