Migratory Ecology of Sea Turtles

Establishing the movement patterns of free-ranging animals is imperative to understanding their behavior and ecology, and is often necessary for designing effective conservation-strategies. This is especially true for migratory species, such as sea turtles, whose long-distance movements form a major component of their life history. In this thesis, I investigated which factors are driving the migratory behavior of the leatherback turtleDermochelys coriacea. Firstly, I examined whether the timing of the nesting season (nesting phenology) is influenced by oceanographic conditions along the pre-nesting migratory route or by variation in population structure. The discovery that nesting phenology appears more influenced by population structure than environmental conditions has implications for the capacity of these animals to adapt to climate change. Leatherback turtle populations may not be expected to respond directly to increasing global temperatures by shifting their nesting phenology, and so nesting under cooler seasonal conditions; however, this could still occur in populations that are increasing in size or average age of the reproductively active individuals. Secondly, I outlined a novel method for identifying behavioral changes in satellite telemetry based on Change-Point Analysis (CPA). Subsequently, I applied it to analyze the post-nesting leatherback turtles tracked from the iSimangaliso Wetland Park, South Africa. Half (n = 8) of the turtles tracked migrated to foraging areas in the shallow coastal waters of the Sofala Banks, Mozambique. Such coastal behavior is very rare in leatherback turtles, which are otherwise often described as \u27pelagic specialists\u27. Overlaying the output of the CPA model with contemporaneous oceanographic data suggests that these coastal habitats are productive, all-year round foraging areas. In contrast, the foraging behavior of the turtles that migrated towards pelagic foraging areas in the Western Indian or South Atlantic Ocean appears to be more associated with ephemeral and dynamic oceanographic processes. Thirdly, I validated the use of stable isotope analysis as a tool for determining the foraging habitats of leatherback turtles. By comparing the stable isotope analysis data to the satellite tracking data, I was also able to infer the potential affects that satellite telemetry devices with high drag can have on migratory behavior. Stable isotope analysis confirmed the importance of the Sofala Banks as a critical foraging habitat for leatherback turtles, but it also previous satellite tracking studies employing high drag devices might have inadvertently been influencing migratory behavior. In essence, altering the very behaviors these devices are used to measure. The findings of this thesis highlight how migratory ecology is influenced by a complex array of factors including population dynamics, individual variation, and environmental conditions. Unraveling these factors can provide surprising insights into the behavior of these animals and help guide the development for future conservation strategies