The research team, led by Bianca S. Santos of Stanford University’s Doerr School of Sustainability together with Larry B. Crowder and Dana K. Briscoe, drew on satellite telemetry from 53 juvenile loggerheads tracked between 2023 and 2025. These animals are part of a broader, decades-long effort known as Project STRETCH, which has involved raising and releasing loggerheads hatched from Japanese nesting beaches and tracking their trans-Pacific journeys. The newly published analysis adds a crucial layer to that legacy: a quantitative description of the ocean conditions the turtles select, and a jurisdictional accounting of where suitable habitat falls under national or international authority.

The technical core of the study rests on two satellite-derived oceanographic variables: sea surface temperature, or SST, and chlorophyll-a concentration, a satellite proxy for the abundance of phytoplankton at the base of the marine food web. By matching each turtle’s transmitted position with contemporaneous measurements of these variables, the researchers characterized the environmental envelope the juveniles actually occupy. The animals were found in waters with a mean sea surface temperature of 17.4 degrees Celsius, with the 10th to 90th percentile range spanning 15.4 to 19.9 degrees Celsius. Chlorophyll-a concentrations averaged 0.14 milligrams per cubic meter, with a 10th to 90th percentile range of 0.07 to 0.22 milligrams per cubic meter.

Those numbers may sound modest, but they encode a great deal of ecology. Loggerhead turtles are ectotherms, meaning their body temperature and activity levels track the surrounding water, so temperature effectively sets the thermal window within which they can forage, grow, and migrate. Chlorophyll-a, meanwhile, marks biologically productive water, the kind of frontal zones and nutrient-rich patches where the small prey items of juvenile loggerheads concentrate. Together, the two variables define a habitat signature: cool but not cold, productive but not eutrophic, characteristic of the transitional waters of the eastern North Pacific where warm subtropical and cooler subarctic water masses meet.

The team then applied these thresholds to a longer archive of oceanographic data spanning 2014 through 2025, a period representing warm ocean conditions in the region, including the influence of large-scale climate oscillations that periodically warm the northeastern Pacific. For each season and year, they mapped where conditions fell within the turtles’ observed environmental envelope, producing inferred patterns of suitable habitat across the entire eastern North Pacific. This approach allowed the researchers to move beyond the limited footprint of individual tracks and ask a broader question: across twelve years of varying ocean conditions, where does juvenile loggerhead habitat actually sit relative to the lines humans draw on the sea?

The answer was strikingly seasonal and strikingly international. Suitable habitat shifted through the year, with between 2 and 31 percent of the United States exclusive economic zone and between 1 and 13 percent of the Mexican exclusive economic zone containing suitable habitat annually. In other words, the amount of turtle-friendly water inside national waters varied enormously from season to season and year to year, expanding and contracting as oceanographic fronts moved and water masses shifted with the climate cycle. A juvenile loggerhead swimming through this dynamic seascape would cross jurisdictional boundaries not once but repeatedly over the course of its development.

The headline figure, however, concerns the high seas. Overall, 86 percent of the suitable habitat for juvenile loggerheads in the eastern North Pacific occurred in areas beyond national jurisdiction, compared with just 6 percent within the United States exclusive economic zone and 8 percent within the Mexican exclusive economic zone. For a population that spends years, possibly decades, in this developmental stage before returning toward western Pacific foraging grounds, the implication is unavoidable: the bulk of its juvenile life unfolds in waters where no single nation holds regulatory authority, and where conservation depends on international cooperation rather than any one country’s domestic protections.

This finding lands at a consequential moment for ocean governance. The high seas have long been a patchwork of sectoral management, with regional fisheries bodies, shipping regulations, and scattered agreements addressing individual activities but no comprehensive framework for biodiversity protection. The recent agreement under the United Nations Convention on the Law of the Sea on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction, often called the BBNJ Agreement, aims to change that by enabling the establishment of marine protected areas on the high seas and requiring environmental impact assessments for activities there. The new loggerhead analysis provides exactly the kind of species-specific, jurisdictionally explicit evidence that such frameworks will need to prioritize particular regions for protection.

The study also underscores why migratory marine species pose such a persistent governance challenge. Unlike seabirds that return to fixed colonies or marine mammals tied to predictable coastal haul-outs, juvenile loggerheads drift through a moving mosaic of thermal fronts and productivity gradients that respect no maritime boundary. As climate change warms and reorganizes ocean conditions, the location and extent of suitable habitat will continue to shift, potentially drawing turtles into new areas, new fisheries interactions, and new management gaps. The authors’ use of a warm-conditions baseline for 2014 through 2025 is a deliberate acknowledgment of this reality: the habitat map of the recent past may not be the habitat map of the coming decades.

For the endangered North Pacific loggerhead population, the practical stakes are concrete. Where juveniles concentrate, they risk entanglement in fishing gear, and the effectiveness of any bycatch mitigation measure depends on knowing when and where turtles and fisheries overlap. The new environmental thresholds, a temperature window centered near 17 degrees Celsius and a chlorophyll-a range around 0.14 milligrams per cubic meter, offer fishery managers and conservation planners a transferable tool: satellite data, freely available in near real time, can now be used to anticipate where suitable juvenile habitat is likely to appear across both national waters and the high seas. Combined with the finding that the overwhelming share of that habitat lies beyond any single nation’s reach, the study makes a clear case that protecting this population’s youngest members is inherently a shared, international enterprise, one that the emerging high seas conservation architecture is only beginning to equip the world to undertake.

Subject of Research: Environmental preferences and jurisdictional distribution of juvenile loggerhead turtles in the eastern North Pacific

Article Title: Environmental preferences and jurisdictional distribution of juvenile loggerheads in the eastern North Pacific

Article References: Santos, B. S., Crowder, L. B., Balazs, G. H., Polovina, J. J., Abreu-Grobois, A., Gaspar, P., Lee Hing, C. A., Jim, L., Kurita, M., Mori, M., Parker, D. M., Rice, M. R., Saito, T., Yamaguchi, N., & Briscoe, D. K. (2026). Environmental preferences and jurisdictional distribution of juvenile loggerheads in the eastern North Pacific. npj Ocean Sustainability. https://doi.org/10.1038/s44183-026-00250-w

Image Credits: AI Generated

DOI: 10.1038/s44183-026-00250-w

Keywords: loggerhead turtles, satellite telemetry, eastern North Pacific, high seas, exclusive economic zone, sea surface temperature, chlorophyll-a, marine conservation, habitat modeling, BBNJ Agreement, endangered species, ocean governance

The research team, led by PhD candidate Diego Bezerra from the university’s School of the Environment, began with a deceptively simple question: which of Australia’s migratory shark and ray species actually depend on waters beyond Australia’s control? To answer it, the researchers shortlisted 29 species that occur within Australian waters and are listed under the Convention on the Conservation of Migratory Species, an international treaty framework designed to protect animals that ignore political borders. They then developed network models, a statistical approach that treats individual movement records as connections between locations, allowing scientists to visualize how populations link distant marine regions into a single, interconnected migratory web.

The results were striking. Five species emerged as confirmed international travelers: whale sharks, blue sharks, shortfin mako sharks, school sharks and white sharks. Some individuals were recorded as far afield as South Africa, New Zealand, Indonesia and Micronesia, while others moved into offshore areas beyond national jurisdiction, the so-called high seas that cover nearly half the planet’s surface. For a white shark tagged off Australia to appear in New Zealand waters, or for a blue shark to span entire ocean basins, is not an anomaly but a routine feature of these animals’ life histories. Their survival, the study makes clear, depends on conditions in many places at once.

That dependence is precisely the problem. Bezerra notes that these long journeys expose sharks and rays to threats across multiple jurisdictions and political boundaries, each with its own laws, enforcement capacity and conservation priorities. A species may enjoy robust protection in one country’s waters only to face intense fishing pressure the moment it crosses an invisible maritime line. Sharks are threatened by overfishing and by being accidentally captured as bycatch when other species are targeted, and blue sharks and school sharks are particularly susceptible to bycatch because they overlap with commercial fisheries across enormous ranges. For a migratory animal, the weakest link in the chain of protection effectively sets the ceiling on its survival.

The study also exposed a more fundamental problem: ignorance. Of the 29 shark and ray species in Australian waters listed under the Convention on the Conservation of Migratory Species, 18 species, or 62 percent, had no published movement information at all. Only eight species had sufficient data to build network models, and just five could be confirmed as crossing international borders. In other words, for roughly two-thirds of the migratory sharks and rays that international treaties are meant to safeguard, scientists cannot say where these animals go, which routes they follow or which jurisdictions they depend on. As Associate Professor Daniel Dunn, a co-author of the study, puts it, you cannot manage migratory species by only looking at one part of their migration, and you cannot manage species or create policy when you have zero information.

Why is the data gap so severe for sharks when migratory birds, sea turtles and marine mammals are tracked in ever-greater numbers? The answer lies partly in the biology of the animals themselves. As Dunn explains, sharks do not breathe air and do not regularly come to the surface, which makes them much harder to tag and to detect. A satellite tag on a seabird transmits its position whenever the bird flies beneath orbiting receivers, and a surfacing whale or turtle offers regular opportunities for data collection. Most sharks, by contrast, spend their lives submerged, so researchers must rely on acoustic receivers placed on the seafloor, pop-up archival tags that must physically detach and float to the surface, or the labor-intensive recapture of marked individuals. Each method captures only a fraction of an animal’s true range, and coverage thins dramatically in deep water and remote ocean regions.

The consequences of this asymmetry ripple through international policy. The Convention on the Conservation of Migratory Species, often called the Bonn Convention, works by listing species across their range and encouraging member states to coordinate protection. But coordination requires evidence, and the new study shows that the evidence base for most migratory sharks and rays is simply too thin to support it. Network models of the kind built by the Queensland team offer a way forward, because they translate scattered tracking records into a quantitative picture of connectivity, identifying which populations link which countries and where conservation investment would deliver the greatest benefit. Yet with only eight of 29 species modeled, the picture remains a sketch rather than a map.

The policy implications are already visible in specific cases. Bezerra points to the whale shark, the world’s largest fish, as a cautionary example. Whale sharks are protected in Australian waters, but they migrate to Indonesia, where fishing could put them in danger. Understanding the different levels of protection between countries, he argues, is essential, because a sanctuary that ends at a maritime boundary offers little comfort to an animal that cannot read one. The same logic applies across the study’s other confirmed migrants: shortfin makos and blue sharks roam into international waters where regional fisheries management organizations, not national laws, govern fishing pressure, and school sharks move between hemispheres along routes that span multiple management regimes.

The researchers argue that wealthy nations with strong domestic protections have a responsibility that extends beyond their own exclusive economic zones. Australia, Bezerra notes, does a relatively good job of protection, but other nations do not always have the same capacity to implement strong measures. His prescription is practical: Australia should support neighboring nations through collaboration and by sharing technology and information. In practice, that could mean joint tagging programs, shared acoustic receiver networks, open data agreements and capacity building for fisheries monitoring in countries that host the same migratory populations but lack the resources to study them. Because the animals themselves are shared, the argument goes, so too should be the science and the tools.

The study lands at a moment when international ocean governance is undergoing its most significant expansion in decades. The recent agreement on biodiversity beyond national jurisdiction, negotiated under the United Nations, aims for the first time to allow the creation of protected areas on the high seas, precisely the offshore regions where the study’s confirmed migrants spend part of their lives. For such instruments to work for sharks and rays, however, they will need the kind of connectivity baseline this research begins to provide. The message from the Queensland team is ultimately one of both warning and opportunity: the ocean’s most endangered migratory predators are already telling scientists where they go, but for most species, the tracking data needed to protect them along the way has yet to be collected. Filling that gap, the researchers say, will require a much larger effort, coordinated across the many nations these remarkable animals call home.

Subject of Research: Migratory connectivity and cross-border conservation of Australian shark and ray species

Article Title: Sharks on the move expose the need for international conservation efforts

Article References: Sharks on the move expose the need for international conservation efforts. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: sharks, rays, migration, conservation biology, satellite tracking, acoustic telemetry, bycatch, high seas, Convention on Migratory Species, Australia, marine policy, University of Queensland