A 170 km journey by a freshwater stingray challenges long-held conservation assumptions

June 8, 2026 dialog A 170 km journey by a freshwater stingray challenges long-held conservation assumptions Lisa Lock Scientific Editor Robert Egan Associate Editor Most sharks and rays inhabit the oceans, but a small proportion thrive in freshwater. Approximately 4% to 5% of all shark and ray species live in tropical and subtropical rivers around the world. Two main ecological strategies can be distinguished among freshwater sharks and rays. There are species that use rivers during part of their life cycle and then return to the ocean. These are called euryhaline species because they can tolerate a wide range of salinities as they move extensively between the sea and rivers. Others cannot tolerate seawater and complete their entire life cycle in freshwater. These are known as obligate freshwater species because they are physiologically restricted to freshwater throughout their lives. The highly fragmented habitat of obligate freshwater species precludes long movements. While euryhaline sharks and rays can move extensively along rivers when entering from and returning to the ocean, obligate freshwater species do not make such long journeys. Indeed, while euryhaline species such as the bull shark (Carcharhinus leucas), sawfishes (Pristis pristis) and whiprays (Urogymnus dalyensis) have been recorded traveling tens to thousands of kilometers along rivers, typical movements by obligate freshwater species such as South American freshwater stingrays Potamotrygon motoro, P. falkneri and P. amandae are always shorter than 8 kilometers (5 miles), even one year after tagging. Our study, published in Aquatic Conservation: Marine and Freshwater Ecosystems, reports that a female giant freshwater stingray (Potamotrygon brachyura) moved 170 kilometers (106 miles) through Argentina's Paraná River system after being tagged and released. This is the longest distance ever recorded for an obligate freshwater ray, challenging long-held assumptions about how these rare animals move and how they should be protected. Freshwater elasmobranchs are among the most threatened vertebrates globally, yet little is known about their behavior. Until now, evidence suggested that obligate freshwater species, unlike their salt-tolerant relatives, tend to move only short distances. As a result, conservation and management strategies generally have been designed at local scales. Our results show that at least some species—the biggest ones—can move across much larger sections of river systems than previously assumed. The discovery comes from a tagging program launched in 2024 in Argentina's middle and lower Paraná River. The initiative involves recreational fishers, who help us tag and release stingrays and report recaptures. In April 2025, a juvenile female measuring 74 centimeters (29 inches) in disk width was tagged in a secondary channel of the river floodplain. Nearly 10 months later, in February 2026, the same individual was recaptured 170 kilometers (106 miles) away along the river network. Based on the time elapsed, the stingray moved an average of about 579 meters (1,900 feet) per day. Such a journey is remarkable not only because of its length but also because it contradicts previous observations from other freshwater stingray species, which showed movements of just a few kilometers over similar or longer periods. The new record places the movement capacity of this species within the range of euryhaline sharks and rays. Body size may help explain this unexpected mobility. The giant freshwater stingray is the largest obligate freshwater ray in the world, reaching up to 1.8 meters (6 feet) in disk width and weighing more than 200 kilograms (441 pounds). Larger freshwater fish species are generally known to travel greater distances, and this pattern may apply here as well. That would make them particularly vulnerable to river fragmentation, such as dams, which can block migration routes and restrict access to key habitats. Our findings also raise broader ecological questions. Are such long journeys common or rare events? How do they influence population connectivity and genetic diversity? And how should conservation strategies adapt? Our findings indicate that protecting isolated areas may not be enough. Effective conservation will likely require coordinated management across entire river systems and provincial jurisdictions. This is key because the giant freshwater stingray is caught for its meat by commercial fishers and as a trophy fish by recreational fishers in Argentina. Freshwater fisheries in Argentina are managed by provinces rather than the federal government. If the movement rate we report is the norm for giant freshwater stingrays, then provincial jurisdictions will not be appropriate for managing fisheries affecting this species. Our observation highlights the importance of maintaining free-flowing rivers, especially in large systems such as the Paraná, where natural connectivity may enable these extensive movements. Protecting such connectivity could be essential not only for stingrays but also for other freshwater megafauna that depend on large-scale habitat access. Understanding how far animals move is key to protecting them. In this case, a single tagged stingray has revealed that the boundaries once assumed may be far too limited. This story is part of Science X Dialog, where researchers can report findings from their published research articles. Visit this page for information about Science X Dialog and how to participate. More information Diego M. Vazquez et al, Long‐Distance Movement by a Giant Freshwater Stingray, Potamotrygon brachyura, Challenges Our View on Movement Ecology and Management of Obligate Freshwater Elasmobranchs, Aquatic Conservation: Marine and Freshwater Ecosystems (2026). DOI: 10.1002/aqc.70400. onlinelibrary.wiley.com/doi/10.1002/aqc.70400 Key concepts animal behaviormigratory speciescommercial fishery resourcesinland fishery resourcesrecreational fishery resourcesfishery managementfreshwater ecosystemsgray sharkssawfishesDiego Martín Vazquez is an Argentine biologist and CONICET researcher whose work focuses on life-history of cartilaginous fishes (sharks, rays and chimeras). After completing his PhD at the Universidad Nacional de Mar del Plata on the reproductive biology of marine oviparous sharks and rays, he shifted his research toward South American freshwater stingrays. His current studies explore reproduction, movement ecology, and conservation needs of these threatened species in the Paraná River. He has authored about 20 scientific publications. Luis Lucifora is an Argentine biologist specializing in the ecology and conservation of sharks, skates and rays. He earned his PhD at Universidad Nacional de Mar del Plata, producing research that informed shark conservation measures in Argentina. After postdoctoral work at Dalhousie University in Canada with leading shark scientists, he returned to Argentina as a CONICET researcher. His current work focuses on threatened freshwater stingrays.