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Climate change influences air temperature and precipitation, and as a direct consequence, the annual discharge pattern in rivers will change as climate warming continues. This has an impact on bedload transport and consequently on aquatic life, because coarse sediments in streams provide important habitat for many species. Salmonids, for example, spawn in gravel, and during their early life stages live in or on top of the substrate. We used a multiple model approach to assess how predicted discharge changes affect bedload transport and the vulnerable early life stages of brown trout (Salmo trutta fario) in a prealpine catchment in Switzerland. In the study area, future discharge scenarios predict an increased frequency of flood occurrence in winter and long-lasting low-flow periods in summer. As a result, bed erosion will become more frequent during winter, leading to less stable spawning grounds and deeper scouring, but during summer, an improvement in habitat diversity can be expected, which is advantageous for young-of-the-year fish. To face the future challenges of climate change, we recommend widening of riverbeds and improvements in longitudinal connectivity.

The failure of river rehabilitation projects is often reported in the literature. One possible reason for this failure is the insufficient consideration of factors degrading riverine ecosystems at large spatio-temporal scales. A precedent analysis of the evolution and significance of these factors at the watershed level is proposed as a prerequisite for a successful rehabilitation project. Based on a watershed-scale approach, we investigated the current and historical states of the fish assemblage and of relevant abiotic factors in the river Rhone, a seventh-order stream in Switzerland scheduled for large-scale rehabilitation. Recent field data gathered by electrofishing and habitat mapping were analysed by means of a mixed model approach and were qualitatively compared compared to historical information derived from topographic maps and documentary sources. The length of the entire active channel has been reduced by 45% (102km) since 1850, representing a significant diminution in lateral connectivity. Our recent fish survey revealed a depleted species set, with only two of 19 historically documented species found. The density of brown trout was generally low, but positively correlated with the presence of cover. Thus, morphological improvements, e.g. through local river widening, offer extensive potential for the restoration of native fish assemblages, but will probably only be successful in combination with a more natural hydrological regime

Rivers are worldwide highly fragmented due to human impacts. This fragmentation has a negative effect on fish movement and dispersal. Many artificial barriers such as river bed sills and small weirs are nowadays replaced by block ramps in order to reestablish longitudinal connectivity for fish in rivers and streams. We studied the upstream passage of several fish species on different types of block ramps with slopes between 3.6 and 13.4%. We conducted translocation experiments in the field based on mark-recapture and on the use of PIT-tags. Temporal movement patterns were observed by an instream antenna. Hydraulic and morphological characteristics of block ramps were measured and compared with fish passage efficiency. Our results clearly showed that upstream passage efficiency differs between fish species, size classes and block ramps. We observed that brown trout (Salmo trutta fario) performed better than bullhead (Cottus gobio) and several cyprinid species on the same block ramps. Passage efficiency of brown trout and chub (Leuciscus cephalus) was size-selective, with small-sized individuals being less successful. For brown trout, size-selectivity became more relevant with increasing slope of ramp. We conclude that block ramps with slopes of >5% are ineffective for the small-sized cyprinid species and that vertical drops within step-pool ramps can hinder successful upstream passage of bullhead

Five wastewater treatment plant effluents were analyzed for known endocrine disrupters and estrogenicity. Estrogenicity was determined by using the yeast estrogen screen (YES) and by measuring the blood plasma vitellogenin (VTG) concentrations in exposed male rainbow trout (Oncorhynchus mykiss). While all wastewater treatment plant effluents contained measurable concentrations of estrogens and gave a positive response with the YES, only at two sites did the male fish have significantly increased VTG blood plasma concentrations after the exposure, compared to pre-exposure concentrations. Estrone (E1) concentrations ranged up to 51ngL−1, estradiol (E2) up to 6ngL−1, and ethinylestradiol (EE2) up to 2ngL−1 in the 90samples analyzed. Alkylphenols, alkylphenolmonoethoxylates and alkylphenoldiethoxylates, even though found at µgL−1 concentrations in effluents from wastewater treatment plants with a significant industrial content, did not contribute much to the overall estrogenicity of the samples taken due to their low relative potency. Expected estrogenicities were calculated from the chemical data for each sample by using the principle of concentration additivity and relative potencies of the various chemicals as determined with the yeast estrogen screen. Measured and calculated estradiol equivalents gave the same order of magnitude and correlated rather well (R 2=0.6)

As part of the Swiss Fischnetz project (network for declining fish yields in Switzerland) studies were carried out to investigate the decline in catches of brown trout. Insufficient YOY (young-of-the-year) recruitment of brown trout due to different abiotic and/or biotic factors was hypothesized as a potential cause of this decline. Quantitative assessments of fish ecology parameters and habitat measurements were carried out at 97 river sites over a two-year period. The main objectives of this study were to document the occurrence and abundance of naturally reproduced YOY trout and to develop an understanding of environmental factors responsible for the observed YOY density. A general linear model (GLM) was used to analyse the influence of selected environmental abiotic and biotic parameters on YOY density. Successful recruitment of YOY trout was observed in all but three of the sites studied. Abundance was correlated with abiotic and biotic factors, such as river width, slope, altitude, substratum condition, and the occurrence of proliferative kidney disease (PKD). The results highlight the importance of small streams for natural YOY recruitment of brown trout and their function as a source of individuals for downstream river sections

Man-made habitat fragmentation is a major concern in river ecology and is expected to have particularly detrimental effects on aquatic species with limited dispersal abilities, like the bullhead (Cottus gobio). We used ten microsatellite markers to investigate small-scale patterns of gene flow, current dispersal and neutral genetic diversity in a morphologically diverse river where fragmented and unfragmented sections could be compared. We found high genetic differentiation between sampling sites with a maximum F ST of 0.32 between sites separated by only 35 km. A significant increase of genetic differentiation with geographical distance was observed in the continuous river section as well as in the full dataset which included headwater populations isolated by anthropogenic barriers. Several lines of evidence are consistent with the hypothesis that such barriers completely block upstream movement while downstream dispersal may be little affected. In the unfragmented habitat, dispersal rates were also higher in the direction of water flow than against it. The resulting asymmetry in gene flow likely contributes to the decrease of genetic variation observed from the lower reaches towards the headwaters, which is particularly pronounced in physically isolated populations. Our findings suggest that headwater populations, due to their isolation and low genetic variation, may be particularly vulnerable to extinction