Investigating Maternal Health and Hatchling Mortality in Leatherback Sea Turtles (Dermochelys coriacea V.)

The reproductive success of leatherback turtles (Dermochelys coriacea) is typically the lowest of the seven sea turtle species. Why this vital rate is decreased has remained unanswered for nearly a century. Recently, detailed postmortem examination of leatherback hatchlings identified muscular pathologies that suggested possible selenium deficiency. High bodily burdens of mercury compounds are associated with selenium depletion. Selenium is a necessary detoxifying nutrient that itself can be toxic at elevated concentrations. Mercury compounds are toxicants with no known biological function. High bodily concentrations of mercury can be detrimental to marine organismal health, reproduction and survival, both directly and indirectly through inducing selenium depletion. The goals of this dissertation are to evaluate several related hypotheses to explain low leatherback nest success. I tested mothers and their offspring and compared two leatherback populations, Florida and St. Croix, for correlations between reproductive success and mercury, selenium and other maternal health parameters. I assayed mercury and selenium concentrations in blood from nesting leatherbacks and their live hatchlings. Additionally, liver levels from dead-in-nest hatchlings were compared with sampled females. Nests from the sampled turtles were excavated and inventoried for hatching and emergence success. I found that reproductive success in leatherbacks correlated with hatchling liver selenium concentrations and the liver selenium to mercury ratios. I established bodily mercury and selenium concentrations in different life stages using multiple tissues from stranded leatherbacks. I found that concentrations of mercury and selenium compounds in the liver of hatchlings and stranded individuals can be at or above levels known to negatively affect organismal health and survival. If these animals had lived, health and/or reproduction could have been compromised. Finally I assayed leatherback prey items collected along the east coast of North America and determined that mercury and selenium tend to bioaccumulate as leatherbacks growth and age. Because leatherbacks take in high volumes of prey, high tissue concentrations of mercury and selenium can result. This study provides the first evidence that chemical contaminants may explain low reproductive success in leatherback sea turtles.