MigrenMer program: synthesis and development of available knowledge on diadromous fish at sea

Abstract

France is home to one of the greatest abundance of diadromous fish in Europe. For several decades now, migratory fish populations have been collapsing, and this decline is common to all species. Pressures all along the land-sea continuum, particularly those induced by human activities, are contributing to this decline. Despite Directives and conventions aimed at protecting these species, management of their marine phase remains difficult due to a lack of knowledge about this marine compartment. To fill this gap, the The MigrenMer project (diadromous fish at sea) was initiated in 2019. As part of this project a database containing 170 000 hauls was created bringing together scientific and commercial data on diadromous fish at sea for analysis. Initial analyses revealed low species occurrence, with marked interspecific disparities. The database was also used to develop diadromous fish at sea distribution models at a North-East Atlantic and Mediterranean scale. An initial hierarchical model confirmed the coastal distribution of species, gear types most likely to bycatch these species and their use of Natura 2000 Habitat Direct MPAs. A follow-on project was then developed to ensure the accuracy of these predictions at a fine scale for management purposes. A modelling framework called CMAP (Combined Model For Accurate Predictions) was also developed and based on the combination of several models providing increased accuracy than Ensemble models. The results highlight the importance of the network of marine protected areas (MPAs) for the conservation of migratory fish species. On average, 55% of their main habitats at sea are located within MPAs that have been specifically designated to ensure their protection. These models are being used to help optimise the protection of diadromous fish during the marine phase of their life cycle.