A sea lamprey, the shad, the European eel and the salmon spend part of their lives in rivers and part in the sea. It is in the sea that we know the least about them, and it is also there that conservation measures remain insufficient. To fill this gap, the European project DiadSea brought together researchers and entities from Portugal, Spain, France and Ireland for three years, under the coordination of the University of Évora/MARE. The final results are presented on Thursday, October 15, in a public session at the University of Évora, according to a press release.
First Comprehensive View in the Atlantic
According to the same source, the project gathered and harmonized 42 data sets, with more than 468 thousand sampling operations, covering 10 species. The work allowed for the first time to build a comprehensive spatial view of the presence of these fish in the Atlantic.
Based on these data, models were developed for the 10 species up to the end of the century. The models predict that the species will expand northward and lose ground in the southernmost areas. The rearrangement of communities is more pronounced in the harsher climate scenario: losses in the south, gains and replacement of species to the north and in open sea. These results allow anticipating which zones could become more vulnerable or gain importance for conservation, and to support more preventive and adaptive management.
The models also show that the marine habitats most suitable for these species depend on the distance to the rivers that sustain the populations. This reinforces the need to manage the sea and the rivers jointly, rather than treating them separately.
“These species know no borders, neither between countries nor between river and sea. To protect them, it is not enough to know more about their life at sea: countries, institutions, managers, researchers and fishers must work together,” says Catarina Mateus, a researcher at MARE-University of Évora and coordinator of DiadSea.
Mondego Fish: Traceability at the Figueira da Foz Market
At the Figueira da Foz fish market, the project tested the origin label “Mondego Fish.” The label distinguishes the sável and the savelha from Mondego freshwater fishing from fish caught at sea or in other zones. By making the origin recognizable along the supply chain, the initiative adds value to a local product and promotes more sustainable fishing. The market operators continued to apply the labels even without the project team present, which shows that the system can become part of the usual sales practices.
New Techniques and Cooperation Among Four Countries
To study the marine phase of species such as the sea lamprey, the shad, the European eel, the salmon and the sea trout, the DiadSea project used a diverse set of advanced techniques. Among them stands out the use of environmental DNA, which allows detecting the species from their genetic traces present in the water without the need to capture them, in addition to genetic analysis, otolith microchemistry and the use of electronic tagging.
Diadromous fish and the pressures they face know no borders. Therefore, in June 2025 the project established the Transnational Observatory for the Conservation of Diadromous Fish, with representatives from the four countries. In September 2025, DiadSea was recognized as a UN Ocean Decade Action.
With the aim of bringing science to the public and raising awareness for the conservation of these species, the project developed various educational resources and outreach materials. Among the initiatives produced are the card game Migro’Ocean, the giant board game The Journey of Migratory Fish, a comic book, explanatory videos and an identification guide available in four languages.
Public Session on October 15
The public session runs from 9:00 a.m. to 5:00 p.m., at the Holy Spirit College of the University of Évora. Throughout the day, the proceedings address monitoring carried out in rivers, estuaries and at sea, migrations and connectivity of populations, the impacts of climate change on the future distribution of the species, as well as the challenges of translating scientific knowledge into practical management.
At 4:15 p.m., the panel discussion “Strengthening Cooperation for the Conservation of Diadromous Fish in Europe” will take place, with MARE, DGRM, ICNF and the Office Français de la Biodiversité.
