Estimation of the Net Nesting Effort of Olive Ridley Arribada Sea Turtles Based on Nest Densities at Ostional Beach, Costa Rica

Ostional Beach, Costa Rica, supports a large mass nesting (arribada) aggregation of Olive Ridley Sea Turtles (Lepidochelys olivacea). A large number of egg clutches is lost to egg harvest and to nest destruction by nesting females after every arribada. Accordingly, the purpose of our study was to generate estimates of the net number of clutches left incubating from clutch densities with the use of a quadrat methodology, and to compare these data with nesting population estimates resulting from the strip transect in time methodology that is currently applied. After the conclusion of each arribada, we randomly performed 50 excavations in 1-m(2) quadrats to count the number of clutches present. We extrapolated quadrat density data to the entire nesting area of the beach to estimate the total number of clutches remaining following each arribada and egg harvest. The mean total clutch density was 4.09 +/- 0.18 SE nests/m(2). Our results showed that quadrat and transect estimate differences ranged from 0.04 to 52.6%, with quadrat estimates typically being lower. Our results demonstrated that, in the rainy season, a large number of clutches (47.4-99.9%) was left incubating in the beach after every arribada and egg harvest. By omitting clutches that were harvested or destroyed throughout the arribada, we evaluated the reproductive potential and estimated the magnitude of clutch loss on Ostional Beach, both of which play important roles in the management of the egg harvest as a sustainable conservation strategy.