Environmental Impact of Undular Tidal Bores in Tropical Rivers

A tidal bore impacts significantly on the estuarine ecosystem, although little is known on the flow field, mixing and sediment motion beneath tidal bores. In the absence of detailed systematic field measurements, a quasi-steady flow analogy was applied to investigate undular tidal bores with inflow Froude numbers between 1.25 and 1.6. Experimental results indicated that rapid flow redistributions occur beneath the free-surface undulations, with significant variations in bed shear stress between wave crests and troughs. Dynamic similarity was used to predict detailed flow characteristics of undular tidal bores. The effects of periodic loading on river sediments, scour of river bed and flow mixing behind the bore are discussed. A better understanding of these processes will contribute to better management practices in tidal bore affected rivers, including the Styx and Daly rivers in tropical Australia

Apprendre du passé pour prédire le futur : réponses des poissons migrateurs amphihalins européens au changement climatique

International audienceClimate change can have an effect on species distributions. The 1900 distribution and potential future distribution of diadromous fish in Europe, North Africa, and the Middle East were explored using generalized additive models (GAMs) and selected habitat characteristics of 196 basins. Robust presenceabsence models were built for 20 of the 28 diadromous species in the study area using longitude, annual temperature, drainage surface area, annual precipitation, and source elevation as explanatory variables. Inspection of the relationship between each variable and species presenceabsence revealed that the GAMs were generally interpretable and plausible. Given the predicted rise in annual temperature in climate models ranging between 18C and 78C by 2100, the fish species were classified according to those losing suitable basins, those gaining suitable basins, and those showing little or no change. It was found that the climate envelopes based on temperature and precipitation for diadromous species would, in general, be shifted farther northeastwards by 2100, and these shifting ranges were comparable with those assessed in other studies. The uncertain future of some species was highlighted, and it was concluded that conservation policy and management plans will need to be revised in the face of climate change

Identification of diadromous fish species on which to focus river restoration: an example using an eco-anthropological approach (the Seine basin, France)

International audienceThe Seine River, like other large and developed European river basins, has lost most of its native diadromous fish populations since the Industrial Revolution. A restoration program has been planned to recover water quality and fish biodiversity in the Seine basin. In this prospective study, we used a dual approach (ecological and anthropological)to prioritize the 11 historic diadromous fish species for restoration. Using generalized additive models and geographic information systems, we assessed which species would have the highest probability of recovery and drew maps of their potential favorable habitats. Three fish appear to be good candidates as flagship species for a recovery plan: smelt Osmerus eperlanus, which has came back into the lower part of the basin; Allis shad Alosa alosa, a few individuals of which have recently been observed upstream from Paris, France; and brown trout Salmo trutta, which is limited to estuarine tributaries. Our anthropological survey revealed that for most citizens polled, these species have no particular significance. These citizens are not in favor of these fish species' recovery because it would lead to changes (e.g., to restore the upstreamdownstream connectivity) and new constraints (e.g., rules of management). To address this potential conflict, we studied a conciliation process with the human inhabitants from one subbasin