Reconstructing long-term trajectories of fish assemblages using historical data: the Seine River basin (France) during the last two centuries

International audienceWe used historical sources from the end of the nineteenth to the mid-twentieth century and current data to retrace fish assemblage trajectories for the past 150 years on 29 river stretches distributed throughout the Seine River basin. We based our analyses on species presence/absence, occurrence of amphidromous and non-native species, and species ecological traits related to habitat preference, oxygen and temperature requirements, and diet. In accordance with general trends observed for Western Europe, we detected a general decline of amphidromous species and an increase in nonnative species, even if, at some sites, several non-native species were extirpated. These changes affecting amphidromous and non-native species led to a weak increase in beta-diversity in fish assemblages. Independently of amphidromous and non-native species, for a reduced set of sites, we noted that changes in the balance of ecological traits over time, trace, in a consistent way, the major steps that affected watercourses like waterway development, increasing pollution, dam construction, or, locally, the recent wastewater treatment improvement. Despite local variations, we found contrasted trends between, on one hand, large rivers and/or catchments which had experienced strong expansion in human population, where fish assemblages had deteriorated, and, on the other hand, upstream catchments, with a declining human population, where fish assemblages showed signs of improvement. Because our results suggested that long-term changes affecting fish assemblages cannot be summarized as an unequivocal gradual degradation, we questioned the use of historical data to define ecological reference conditions for river assessment and management purposes

Réponse des peuplements de poissons à l'urbanisation et aux altérations anthropiques à long terme des fleuves

National audienceRéponse des peuplements de poissons à l'urbanisation et aux altérations anthropiques à long terme des fleuves

Changes in Fish Communities of the Seine Basin over a Long-Term Perspective

International audienceAbstract Using both historical and current data, we retrace the long-term evolution of fish assemblages in the Seine River basin since 1880, from headwaters to upstream of the Seine River estuary. Successive phases are observed, related to anthropogenic impacts on habitat conditions and river water quality. Temporal trajectories were thus reconstructed on several reaches based on the change of the proportion of species’ ecological traits, in order to detect the main drivers of alteration. Contrasted trends occur between large rivers and small streams of the basin. In this context, migratory fish declined, whereas the proportion of non-native species increased in the fish community of the Seine River