To understand the long-term fate of fish assemblages in the context of global change and to design efficient restoration measures in river management, it is essential to consider the historical component of these ecosystems. The human-impacted Seine River Basin is a relevant case that has experienced the extinction of diadromous fishes over the last two centuries and has recently witnessed the recolonization of some species. One key issue is to understand the historical evolution of habitat accessibility for these migratory species. Thanks to the unique availability of historical, mainly hand-written sources of multiple types (river engineering projects, navigation maps, paper-based databases on oxygen, etc.), we documented and integrated, in a geographic information system-based database, the changes to physical and chemical barriers in the Seine River from the sea to Paris for three time periods (1900s, 1970s, and 2010s). The potential impact of these changes on the runs of three migratory species that have different migratory behaviors—Atlantic salmon, allis shad, and sea lamprey—was evaluated by ecological connectivity modeling, using a least-cost approach that integrates distance, costs, and risks related to barriers. We found that accessibility was contrasted between species, emphasizing the crucial role of the migration type, period, and level of tolerance to low dissolved oxygen values. The highest disruption of ecological connectivity was visible in the 1970s, when the effects of large hypoxic areas were compounded by those of impassable navigation weirs (i.e., without fish passes). As the approach was able to reveal the relative contribution of physical and chemical barriers on overall functional connectivity, it may constitute a model work in assessing the functioning of large river ecosystems.

To fill the gap between microhabitat and landscape scale habitat models for freshwater fish, it is becoming increasingly common practice to adopt a continuous view of riverscapes, thus allowing a better understanding of the processes in place at the river management level (segments of 1–100 km). The aim of this study was to test the effects of the spatial structure of habitat on fish distribution at this scale. Inferred habitat relationships were generated using spatial metrics adapted from landscape ecology. These were calculated for two species of multi-habitat cyprinid fish in a 25-km long segment of the Seine River. A spatially continuous survey was then designed to acquire fish sampling data relating to the riverscape. Explanatory models were devised to quantify the extent to which environmental and spatial variables could describe fish distribution patterns. Spatially continuous sampling of feeding habitats at dawn and dusk provided greater understanding of the spatial distribution of common barbel (Barbus barbus, L.) and nase (Chondrostoma nasus, L.). Fish observations were aggregated longitudinally in neighboring feeding habitat patches, with the highest abundance found in patches with the best local conditions. The species were present for large feeding patches, as well as for a higher proximity index for those patches. This result emphasized the importance of the supplementation of feeding habitats. By quantifying spatial habitat relationships using spatial metrics, it was possible to identify the best suited configuration of functional habitats to the needs of shoals. At present, most conservation work focuses on restoring local habitats. There is also growing interest in large-scale fish management, which has been encouraged by the advent of metapopulation theory. This study highlights the need for greater work at a third, intermediate scale that is no less significant: restoring daily and seasonal movements between functional habitats.

Bien qu’elles représentent environ 80 % du réseau hydrographique francilien, les petites rivières périurbaines des environs de Paris sont peu étudiées. Ces cours d’eau de petites dimensions, à relativement faible énergie, et dont les ajustements morphologiques sont assez lents, se démarquent par la pluralité d’acteurs (publics et privés) que mobilise leur statut non domanial, et par la diversité des situations géographiques dans lesquelles ils s’insèrent. Les espaces périurbains sont essentiellement affectés par l’intensification des pratiques agricoles et l’étalement urbain, lequel, en entraînant la multiplication des réseaux hydrauliques artificiels et des surfaces imperméables, augmente le risque de ruissellement. L’augmentation des rejets potentiels urbains et agricoles engendrerait une forte dégradation écologique. Cette étude se concentre sur trois rivières franciliennes : la Biberonne, la Mérantaise et le Morbras. Deux méthodes ont été employées en vue de déterminer la relation entre leurs altérations hydrogéomorphologique et biologique : la première est la Caractérisation Hydrogéomorphologique des Cours d’Eau (CARHYCE), et la seconde est l’évaluation de la qualité écologique d’un cours d’eau à partir du peuplement de macroinvertébrés benthiques (Indice Invertébrés Multimétrique - I2M2). Il ressort du rapport largeur/profondeur de ces trois rivières qu'elles tendent vers une incision du chenal avec une charge de fond quasi-absente (bedrock apparent). L'appauvrissement du peuplement de macroinvertébrés révèle une mauvaise qualité du milieu et semble répondre à un gradient de conditions physiques locales. Ces résultats montrent le poids des transformations urbaines sur les altérations contemporaines de la qualité biophysique des milieux aquatiques de ces rivières et soulignent la nécessité d’étudier plus précisément la relation entre les altérations hydrogéomorphologique et biologique.

Cet article de synthèse, fruit du travail d’un collectif interdisciplinaire de chercheuses et chercheurs du Réseau des Zones Ateliers françaises (CNRS), porte sur la mise en œuvre des projets de restauration de la continuité écologique des cours d’eau. Les projets de restauration se trouvent au cœur d’une importante controverse dans l’espace public français depuis plusieurs années. En particulier, certains acteurs questionnent la pertinence de la politique publique visant à effacer les ouvrages qui contribuent à l’interruption de la continuité des cours d’eau. Dans cet article, nous faisons d’abord une synthèse des effets connus de l’interruption de la continuité dans ses dimensions longitudinale, latérale et verticale vis-à-vis des enjeux biophysiques et socio-économiques. Eu égard à la complexité des processus concernés, de la variabilité des contextes territoriaux possibles et des incertitudes associées à la restauration des hydrosystèmes, notre analyse révèle la nécessité d’inscrire les projets de restauration dans un projet plus large autour de la gestion des ressources aquatiques mené à l’échelle d’un territoire et reposant sur un processus décisionnel participatif. La décision de restaurer ou de ne pas restaurer la continuité ne peut s’en remettre exclusivement à la science et à l’expertise technique. Forts de ce constat, nous proposons ici une démarche stratégique pour adresser les défis qui entourent la restauration de la continuité. Cette démarche intègre dix points de vigilance à prendre en compte pour la mise en œuvre de projets de restauration à la fois soutenus par les différents acteurs et efficaces par rapport aux objectifs définis.

Aim: Invasive species are among the most important drivers of native species declines, and cause serious economic and ecological costs. Globally, Europe is a hotspot for freshwater non‐native species, especially among macroinvertebrates and fish, and inland navigation is thought to be a major driver of their spread. However, the degree to which different aspects of navigation (i.e., ship traffic vs. infrastructures) contribute to non‐native species spread, establishment and distribution has not yet been quantified. Our study set out to determine the role that navigation plays in the distribution of Western European freshwater established non‐native species, and which aspects of navigation are most responsible. Additionally, we aimed to identify the spatial scale at which these navigation pressures operate, and what ecological characteristics may influence species' response to navigation. Location: Europe. Methods: We extracted data from the Global Biodiversity Information Facility (GBIF) to identify occurrences of established non‐native species in Europe from the past 30 years. Using over 500,000 occurrences, we mapped the coverage of over 250 established non‐native species and paired this with pan‐European data on inland ship traffic, navigation infrastructure and environmental data. Results: We found that the greatest predictor of non‐native species richness and occurrences was the presence of a shipping canal in the subcatchment. This held true for both fish and macroinvertebrates at fine and large spatial scales. Temperature was also an important predictor of non‐native species distribution. We found these positive associations to be strongest for generalist fish species, molluscs and crustaceans. Main Conclusions: Freshwater navigation, especially canals, is an important vector for non‐native species establishment, and highlights the need for frequent monitoring and mitigation. Given that increased temperatures are associated with establishment success, climate change may also play an increased role in non‐native species dispersal.