A new study from the University of California Santa Cruz has tracked 14 species of migratory marine predators such as leatherback turtles and blue whales to examine how their movements relate to the geopolitical boundaries of the Pacific Ocean. The research will provide critical insight for developing international agreements that are needed to manage and conserve these animals in the high seas.
“If a species spends most of its time in the jurisdiction of one or two countries, conservation and management is a much easier issue than it is for species that migrate through many different countries,” said study co-author Professor Daniel Costa.
For example, the leatherback sea turtle, which is the largest living turtle and a critically endangered species, visits more than 30 countries during migrations.
“For these highly migratory species, we wanted to know how many jurisdictional regions they go through and how much time they spend in the open ocean beyond the jurisdiction of any one country,” said Professor Costa.
Since 2016, members of the United Nations have been working to negotiate a global treaty for conservation and management in the open ocean waters. Under the current international law, every coastal nation can establish an exclusive economic zone (EEZ) extending up to 200 nautical miles from shore. The country has exclusive rights to exploit resources and regulate fisheries within its established EEZ.
Study first author Autumn-Lynn Harrison began the study as a graduate student in Professor Costa’s lab at UC Santa Cruz.
“I wanted to see if we could predict when during the year a species would be in the waters of a particular country,” said Harrison. “Some of these animals are mostly hidden beneath the sea, so being able to show with tracking data which countries they are in can help us understand who should be cooperating to manage these species.”
Harrison attended meetings on issues related to the high seas, which focused her attention on the time migratory species spend in waters outside of any country’s jurisdiction.
“Figuring out how much time these animals spend in the high seas was directly motivated by questions I was being asked by policy makers who are interested in high seas conservation,” said Harrison.
Many of the top marine predators are declining or threatened, and this is partially due to the fact that their mobility exposes them to a wide array of threats in different parts of the ocean.
Professor Costa is a co-founder of the Tagging of Pacific Predators (TOPP), which has produced one of the most extensive data sets available on the movements of large marine animals.
White sharks are protected in U.S. and Mexican waters, but the TOPP data show that they spend about 60 percent of their time in the high seas. Leatherback turtles, Laysan albatross, Pacific bluefin tuna, and sooty shearwaters also travel across the Pacific Ocean during their migrations.
“Bluefin tuna breed in the western North Pacific, then cross the Pacific Ocean to feed in the California Current off the United States and Mexico,” said Professor Costa. “Sooty shearwaters not only cross the open ocean, they use the entire Pacific Ocean from north to south and go through the jurisdictions of more than 30 different countries.”
Harrison will present the team’s findings at the U.N. Intergovernmental Conference in September, which will be the first to negotiate an international agreement on the conservation of marine biological diversity beyond areas of national jurisdiction.
“These migratory species are a shared heritage, and this paper shows their international travels better than ever before,” said Harrison. “The first step to protect them is knowing where they are over their annual cycle and promoting international agreements to manage the threats they may face across several countries.”
The study is published in the journal Nature Ecology & Evolution.
Image Credit: Alex Eilers