Today in the scientific journal Marine Ecology Progress Series, Stanford University marine biologist, and Center of Oceans Solutions’ Marine Spatial Planning Director Dr. George Shillinger and his colleagues published their findings from a three-year study of leatherback sea turtles tagged with satellite transmitters at Playa Grande, Costa Rica. By following the movements and diving behavior of these turtles, in the context of the oceanographic conditions around them, the researchers were able to identify the habitat most suitable for them. With this information, it is possible to predict where leatherbacks will go in the open ocean based on oceanographic conditions – and thus to help reduce mortality through interactions with fisheries or other human activities on the high seas.
Leatherback sea turtles are the largest and widest-ranging turtle species, and they spend most of their long lives in the open ocean. Unfortunately, their numbers have declined precipitously in the wild – especially in the Pacific. This decline is attributed to a variety of human activities, including habitat loss, poaching of both turtles and their eggs, and fisheries bycatch. Although there have been significant conservation efforts aimed at protecting the turtles on their nesting beaches, little information has been available to help protect them at sea where they spend the majority of their time.
Working on the beaches of northwest Costa Rica, Shillinger and his colleagues attached electronic tags to female leatherback sea turtles that had come ashore to lay eggs. A total of 46 turtles were tagged from 2004 to 2007. After leaving the beaches, the turtles were followed for an average of 217 days as they traveled offshore into the southeastern Pacific Ocean. During these journeys, the tags recorded information about location, depth and temperature – giving the researchers a detailed profile of their behavior in the wild. By studying the frequency and depth of their dives, the researchers were able to identify specific behavior types – some of which appeared to be characteristic of traveling, and others of foraging for food.
Using a sophisticated computer model, the turtle behavior data was combined with satellite-based measurements of oceanographic conditions including sea surface temperature, chlorophyll a (indicative of the presence of microscopic plant life called “phytoplankton,” which forms the base of the ocean food web), and Ekman upwelling – which is associated with the presence of nutrient-rich water rising to the surface. By analyzing all these factors together, the researchers demonstrated that the turtles’ foraging behavior was associated with regions of cooler surface temperatures, higher chlorophyll aconcentrations, and strong upwelling – all of which can be observed from earth-orbiting satellites.
“The ability to predict where leatherback sea turtles go is a critical first step in being able to protect these animals in the open ocean,” says Shillinger. “Our improved understanding regarding the forces that shape their movements, will help to inform our efforts to reduce fisheries-turtles interactions, and to advance ecosystem-based marine spatial planning efforts in the Pacific.”
One of the fundamental goals of the TOPP program was to explore whether ecosystem-level tagging studies, carried out on multiple species over an extended time period, could help inform ecosystem-based resource management. This study demonstrates the viability of such an approach.