Eight female broadnose sevengill sharks (Notorynchus cepedianus) followed the same rough course after being tagged in the Ría Deseado in southern Patagonia. According to preliminary results of an Argentine research project, all animals moved north, passed the coasts of the provinces Chubut and Buenos Aires and partially reached the waters of Uruguay.
The data supports the assumption that the sharks use a common migration corridor in the southwestern Atlantic. This means that a single annual cycle connects habitats in several Argentine provinces and at least one other country. Protective measures, fishing rules and data exchange should take this cross-border movement into account.
Eight reproductive females with satellite transmitters
The crucial tagging campaign took place from January 29 to February 5, 2025 at Puerto Deseado in Santa Cruz Province. Selected sharks received satellite transmitters that recorded depth, water temperature and movements over several months. At the end of the measurement period, these tags detach from the animal, rise to the surface and transmit the stored data via the satellite system Argos.
All eight pursued females moved north. The agreement is striking, but the sample remains small and only includes reproductive females. It is not yet possible to determine from these initial data whether males, young animals or animals use the same route with the same regularity in other years.
A recapture after more than 1,700 kilometres
The satellite tracks match older marker data. CESIMAR-CONICET reported in November 2025 of a female that had been conventionally tagged in the Ría de Puerto Deseado in February of the same year. On October 10, it was recaptured in the waters of Uruguayan Departamento Rocha, more than 1,700 kilometers from the marking site.
The fishermen discovered the numbered tag near the dorsal fin and reported the find to the Uruguayan Fisheries Authority DINARA. The approximately 187 centimeter long animal had covered the distance in around eight months. Such recaptures do not provide a complete route, but they confirm the start and end points of a long-distance migration.
On October 23, just 13 days later, a second marked broadnose sevengill shark was found off La Floresta in Uruguay. The adult male shark, 191 centimeters long and weighing around 40 kilograms, was tagged at Bahía Blanca in October 2022. His mark came from another Argentine program. Both reports show the value of consistently labeled brands and cooperation with fishermen.
A migration model becomes verifiable
The CESIMAR team around Alejo Irigoyen and Gastón Trobbiani had investigated deposits in Santa Cruz, Chubut, Río Negro and Buenos Aires for more than ten years. This resulted in a theoretical model according to which broadnose sevengill sharks migrate along the southwestern Atlantic between Argentina, Uruguay and the south of Brazil.
The recaptures in Uruguay and the new satellite tracks are independent pieces of evidence that support key parts of this model. However, they do not yet provide a complete route for the entire population. This requires more tagged animals, several years and an analysis of the question of when and why individual sharks use certain parts of the coast.
Why the Ría Deseado is important
The Ría Deseado is a protected area of the Santa Cruz province and one of the southernmost known places where broadnose sevengill sharks temporarily gather. This means that the area is not just the starting point for a long hike. It could fulfill a recurring function in the life cycle of animals.
The project therefore not only examines the distances covered. It also asks how broadnose sevengill sharks and dog sharks use the Ría Deseado and other parts of the coast of Santa Cruz and whether individual animals return at certain times. Only this connection between movement and length of stay shows which areas are particularly important for protective measures.
Satellites, underwater cameras and fishing knowledge
The research team combines satellite transmitters with conventional tags, length and weight measurements, photography, baited underwater cameras and interviews with recreational fishermen. Behind the project are the Fundación Por el Mar, the Tag a Giant Foundation, the Proyecto Arrecife from CENPAT-CONICET and the Consejo Agrario Provincial from Santa Cruz.
Recreational and professional fishermen play a dual role. They help capture and release live animals for tagging and can report subsequent recaptures. Without this feedback, many conventional brands would remain scientifically worthless because the second data point would be missing.
From Patagonia to Sharks International 2026
Carolina Pantano from Fundación Por el Mar presented the first results in May at Sharks International 2026 in Colombo. The conference brought together researchers, conservation organizations and experts on sharks, rays and chimeras. For the project, the presentation was an opportunity to make the Ría Deseado internationally visible as a previously little-known southern Patagonian shark habitat.
However, a conference presentation and reports from authorities are not a substitute for a complete specialist publication. Currently, neither all of the individual satellite tracks nor the statistical analysis of the eight females have been published in the linked messages. The results should therefore be understood as strong preliminary evidence and not as a conclusively described migration pattern.
Shark protection must cross borders
The central consequence is nevertheless clear: a shark that uses a protected gathering place in Santa Cruz in the summer can swim through fisheries off Buenos Aires or Uruguay months later. Local protection can secure important habitat, but cannot cover all risks throughout the migration.
Effective management therefore requires coordinated rules, comparable catch data and a rapid exchange of tagging finds between Argentina and Uruguay. Future satellite data could also show where the animals stay for long periods of time and where their routes overlap with intensive fishing.
Aaron Scheiner, CC BY-SA 4.0, via Wikimedia Commons. Edited: Cropping to 2:1 as well as careful color, contrast and sharpness optimization.
