Kemp's ridley Lepidochelys kempii nesting abundance in Texas, USA: a novel approach using genetics to improve population census

Accurate estimates of the annual numbers of nesting females are critical for assessing sea turtle populations. Nesting by Kemp's ridley Lepidochelys kempii turtles has significantly increased at Padre Island National Seashore and nearby beaches in Texas, USA. Four nests were observed in Texas during 1995 and a record of 209 in 2012. However, it is unclear how many clutches are laid by the same females. We used a genetic approach to infer the number of individual nesters from genotypes determined from dead embryos and hatchlings sampled from clutches. Mitochondrial DNA sequencing was combined with nuclear DNA analysis at 10 microsatellite loci to match genotypes for nesters and offspring of unknown parentage in over 50 % of the unassigned nests. Our results indicate that traditional methods, based on observed tagged turtles, have underestimated the number of Kemp's ridleys nesting in Texas. We demonstrate how genetic approaches can be incorporated into population assessments when direct census of adult animals is not feasible. This approach also provides a basis to apply capture mark recapture techniques to assess the impact of events, such as the recent oil spill, on the population via sampling of nests to identify and track individual nesters over time.