Tagging and tracking leatherback sea turtles has produced new insights into the turtles’ behavior in a part of the South Pacific Ocean long considered an oceanic desert. According to researchers at Stanford University, the new data will help researchers predict the turtles’ movements in the ever-changing environment of the open ocean, with the goal of reducing the impact of fishing on the endangered leatherback population.
Leatherback turtles have suffered a massive 90 percent drop in their population in the eastern Pacific Ocean over the last 20-plus years, largely at the hands of humans
Now, new data from a 5-year-long project tagging and tracking the turtles are providing insights into their behavior, explaining why they congregate for months in what appeared to be one of the most nutrient-poor regions in the oceans, the South Pacific Gyre, and also helping researchers predict their movements on the high seas.
This new view of the lives of leatherbacks could offer a way to keep the turtles out of harm’s way and give their numbers a chance to rebound.
Until now, researchers didn’t know why the leatherbacks that nest at Playa Grande in Costa Rica headed for the gyre and lingered for months. Satellite surface data suggested that this area spanning the Pacific Ocean between South America and New Zealand, from the low to mid-latitudes, appeared to be a virtual desert in the ocean, largely devoid of nutrients.
However, the presence of substantial tuna and swordfish fisheries within the region suggested there must be ample forage of some sort available.
Because only limited data exist concerning the diversity, abundance and distribution of the leatherback’s favorite prey – gelatinous zooplankton, such as jellyfish – within the South Pacific Gyre, no one knew whether the turtles had food down there or not.
But the data that came back from the tagged turtles suggest there may be plenty of jellyfish on which to feast.
One of the biggest hazards leatherbacks face on the high seas is longline fishing, a widely used approach for capturing commercially valuable species such as tuna and swordfish. The turtles also face fishing pressure from gill nets and longlines as they swim through coastal waters on their way out to the open ocean.
The problem, George Shillinger, lead author of a paper to be published in Marine Ecology Progress Series, said, is that areas that attract commercially desirable species also tend to be attractive to leatherbacks and other non-targeted species, known as by-catch.
Temporary closure of certain areas – breeding zones, migration routes and rich foraging habitats – when turtles are most likely to be concentrated there is one possible measure to protect turtles. Modification of fishing techniques, such as deploying hooks at the depths that are least likely to be occupied by turtles, could also help.