Meeting Abstract
15.2 Jan. 4 Density-dependent effects on hatching success in olive ridley sea turtles HONARVAR, Shaya*; O’CONNOR, Michael P.; SPOTILA, James R.; Drexel University; Drexel University; Drexel University sh333@drexel.edu
Historically, the olive ridley arribada at Playa Nancite, Costa Rica has been one of the largest arribadas in the eastern Pacific with 100,000 nesting females in a year. Recently the olive ridley arribada at Playa Nancite has declined drastically. One hypothesis proposed to explain the decline on Playa Nancite is low hatching success such that recruitment to the population is insufficient to balance losses. This hypothesis was examined by density-dependent effects on hatching success and their underlying mechanisms by experimentally manipulating nest densities on the nesting beach. We set up four nest density treatments in 5 experimental blocks. Each block contained a control plot without nests, a low density plot with two nests, a moderate density plot with 5 nests and a high density plot with 9 nests per square meter. Only 70 eggs were relocated in each nest and 10 other eggs were weighed during relocation and 10 hatchlings per nest were weighed at emergence. The number of hatchlings per nest was counted in each plot. CO2 and O2 concentrations and temperature were measured in each plot both within a nest and in sand adjacent to a nest frequently during incubation. We found that experimental nest densities affected hatching success with highest density having lowest hatching success. Further, higher nest density lead to lower O2 levels and higher CO2 levels in the nest with greater changes in the latter part of the incubation. Highest temperatures were recorded in high density areas. Temperatures were lower in the sand surrounding the nest than in the nest. We found no statistically significant difference in hatching mass in different densities when compared to original egg mass. Long term failure in production of hatchlings due to historic high densities could contribute to the decline of arribadas on Playa Nancite.
