Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John A. Musick


There currently exists a major dichotomy in the nesting population trends of leatherback turtles (Dermochelys coriacea) worldwide. Eastern Pacific populations have been declining precipitously while populations in the Atlantic and western Indian Oceans have been either stable or increasing. The populations in the western Pacific have also declined with some near extirpation. Factors attributed to the Pacific population decline are incidental fishery mortality and egg harvesting. Fishery mortality occurs throughout all basins, and with the exception of the western Pacific population, egg harvesting has not been a major factor at the major nesting complexes for almost two decades. Populations in the Atlantic and western Indian Oceans currently tolerate mortality from top-down factors, while the eastern Pacific populations continue to decline. Therefore, trophic forcing from bottom-up factors may be the major cause of this dichotomy. This study addressed the effects of bottom-up and climatic forcing on leatherback populations worldwide, with an emphasis on leatherbacks in the eastern Pacific. Nesting leatherbacks in the eastern Pacific were highly influenced by ENSO. Cool, highly productive La Nina events caused a high nesting probability whereas warm, less productive El Nino events caused a low probability. Areas of the equatorial Pacific that produced the most accurate nesting estimates, as indicated by sea surface temperature anomalies, were located around the northeast. Foraging conditions in the eastern equatorial Pacific were a function of ENSO governed primary production transitions that determined leatherback nesting numbers in Costa Rica. It appeared that resource availability in the temperate, southeastern Pacific was not sufficient on its own to support vitellogenesis and the nesting process. While coastal foragers were common among most leatherback populations worldwide, they were rare within the eastern Pacific population, possibly from high mortality associated with coastal gillnet fisheries along Central and South America. Among populations worldwide, eastern Pacific leatherbacks had the lowest reproductive output derived from climate driven, inconsistent resource availability. This study demonstrated that the highly sensitive nature of eastern Pacific leatherbacks to anthropogenic mortality derived from interannual and multidecadal climate variation in their foraging areas, thus accounting for their decline rates despite continued beach protection.



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