Reproductive Biology of Atlantic Leatherback Sea Turtles at Sandy Point, St. Croix: The First 30 Years

Abstract The nesting population of leatherback sea turtles at the Sandy Point National Wildlife Refuge (SPNWR), Sandy Point, St. Croix, US Virgin Islands, has been comprehensively studied since 1981. Nesting and hatching data are reported here for the first 30 yrs of the research and conservation project. Because of intense nest relocation and conservation efforts, the population initially showed a steady increase in numbers, with the most dramatic rise occurring between 1997 and 2001. In spite of continued efforts, however, this recovery began to stall in the decade from 2000 to 2010. Analysis of nesting data, including specific reproductive parameters such as recruitment rate, remigration interval, and productivity (number of nests laid, hatching success) during this time frame, in conjunction with historical data, provided an opportunity to assess the contribution of these factors to the population dynamics at Sandy Point. Annual reproductive data demonstrated that regardless of overall nesting numbers, odd years consistently exhibited higher nesting numbers (115.6 ± 18.58) than even years (68.4 ± 7.63) (p < 0.01). The average annual remigration interval increased over the study period with a record high of 3.41 ± 0.18 yrs observed in 2008. A steady decline in average nests laid was observed (R2 = 0.84) between 1992 and 2010, with a record low of 3.60 ± 2.16 nests per turtle in 2010. Hatching success varied over the 30-yr period from a project low of 40.28% ± 23.20% in 2005 to a record high of 67.80% ± 20.31% in 1991. Mean overall hatching success for the first 30 yrs of the project was 58.50% ± 7.75%. Hatching success declined over the course of the project, and the number of hatchlings produced per turtle declined in the 2000s. These factors contributed to a decrease in population productivity and may ultimately have inhibited continued population growth. Over the study period, a stable percentage of remigrants continued to nest at Sandy Point. However, a decreased number and percentage of neophytes was observed, suggesting either a delayed or a decreased recruitment, possibly due to increased age to sexual maturity, an increased mortality of early life stages, or a change in food resources at foraging grounds. These results suggest a population that has slowed growth and that may begin to decline in the future. Further research needs to be conducted to understand possible maternal, physiological, and environmental factors that are impacting these reproductive parameters and, ultimately, affecting the population dynamics at SPNWR.