DiadSea Project: Transnational Cooperation to Improve the Management and Conservation of Diadromous Fish at Sea ^†

Abstract

Diadromous fish provide key ecological and socio-economic services in European Atlantic catchments, yet their marine phase remains poorly understood and weakly integrated into management. Involving nine partners from Portugal, Spain, France and Ireland, the DiadSea Interreg Atlantic Area initiative aims to fill these critical knowledge gaps on the marine and estuarine phases and to translate this information into coordinated conservation and fisheries management tools. To do so, the project combines historical and newly collected fishery-dependent and -independent data (landings, by-catch, cooperative surveys with commercial and recreational fishers) with advanced microchemical, genetic and environmental DNA (eDNA) analyses to characterize marine distributions, mixing areas and connectivity for shads, Atlantic salmon, sea trout, European eel, sea lamprey and other diadromous species. It also includes innovative case studies on lamprey tagging and intestinal metabarcoding, coastal habitat suitability mapping for shads using river plumes and environmental variables, and joint otolith microchemistry–genomics approaches to reassess European eel panmixia and maternal origin at the Atlantic scale. Species distribution models under present and future climate scenarios, specifically RCP4.5 and RCP8.5, are used to identify priority marine areas for conservation, zones of high temporal turnover and key interfaces ensuring longitudinal (river–sea) and latitudinal connectivity, which will feed into an updated interactive web Atlas of diadromous species. In parallel, DiadSea establishes a transnational observatory of stakeholders to harmonize legislation, co-develop adaptive fisheries management plans and produce climate-aware policy guidelines, while capacity-building actions include an origin-labeling scheme for sustainably harvested diadromous fish, educational games and a comic book to raise awareness among younger generations and the wider public. Together, these work packages will deliver the first integrated, marine-focused, evidence-based and decision-support framework for diadromous fishes in the North-Eastern Atlantic, strengthening conservation, sustainable fisheries and stakeholder engagement under ongoing climate change.