Factors affecting population dynamics of eastern pacific leatherback turtles (Dermochelys coriacea)

The leatherback turtle (Dermochelys coriacea) is critically endangered. The population of leatherbacks that nest at Parque Nacional Marino Las Baulas, in Costa Rica declined by 95% in less than 20 years. Annual mortality rate of adults was higher than expected in a natural population and mortality rates of juveniles could double those of a stable population. Conservation efforts since the Park was established in 1991 resulted in higher production of hatchlings per egg laid. However, the overall hatchling output decreased because of the decreasing number of nesting turtles. Simulations on the effect of egg poaching showed that poaching was the most important cause of population decline at Las Baulas. Heavy poaching resulted in a stepwise decline in number of nesting turtles due to consecutive reductions in each nesting stage. The nesting population declined faster and was extirpated sooner with 90% egg poaching than with 20% adult mortality. However, both protection in the ocean from fishing and on the beach are critical to the survival of the population. Behavior of hatchling leatherback turtles on the walk to the water was driven by predation risk. Hatchling leatherback turtles decreased predation risk emerging in groups and dispersing. Straightness of tracks increased during the process of departure and was lower in areas of higher exposure to light pollution. Nest success of leatherback turtles was driven by environmental variability. High temperatures in the nest reduced its success, and high rainfall and low ambient temperatures resulted in higher production of hatchlings. Predicted emergence success was related to El Niño Southern Oscillation (ENSO). Leatherback female turtles increased reproductive success over time by increasing number of eggs, number of clutches and arriving earlier in the season, when hatchling production was greater.In conclusion, the population decline at Las Baulas was mainly caused by egg poaching but is still threatened by high mortality in the ocean. Conservation efforts have been efficient at increasing hatchling production. However, the stochastic nature of nest success and consequently, recruitment rate, may increase the risk of extinction of a population already reduced from past poaching and fisheries.Ph.D., Biological Sciences -- Drexel University, 200