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[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; International audience; The impact of species loss on ecosystems functioning depends on the amount of trait similarity between species, i.e. functional redundancy, but it is also influenced by the order in which species are lost. Here we investigated redundancy and sensitivity patterns across fish assemblages in lakes, rivers and estuaries. Several scenarios of species extinction were simulated to determine whether the loss ofvulnerable species (with high propensity of extinction when facing threats) causes a greater functional alteration than random extinction. Our results indicate that the functional redundancy tended toincrease with species richness in lakes and rivers, but not in estuaries. We demonstrated that i) in the three systems, some combinations of functional traits are supported by non-redundant species, ii) rarespecies in rivers and estuaries support singular functions not shared by dominant species, iii) the loss of vulnerable species can induce greater functional alteration in rivers than in lakes and estuaries. Overall, the functional structure of fish assemblages in rivers is weakly buffered against species extinction because vulnerable species support singular functions. More specifically, a hotspot of functionalsensitivity was highlighted in the Iberian Peninsula, which emphasizes the usefulness of quantitative criteria to determine conservation priorities.

International audience; The complementarity of two high-resolution spatiotemporal acoustic methods, telemetry and hydroacoustics, was evaluated during the same time window to obtain fish distribution in a canyon-shaped reservoir, the Bariousses Reservoir (France). These methods act at an individual scale for telemetry and a community scale for hydroacoustics. The temporal scales are also different: telemetry offers continuous and long-term monitoring while a "snapshot" view is given by hydroacoustics. Day and night hydroacoustic surveys were carried out in this reservoir, during a 24-hour period in spring, using vertical and near-surface horizontal beaming. During this time window, 11 adult fish (length: 22-57 cm) from three species (roach, perch, and pikeperch) were tracked by telemetry. Four metrics were calculated with data collected by application of the two methods: distances to the nearest bank, distances to the tributary, fish depth, and bottom depth at the location. The contrasting (distance to the nearest bank, bottom depth) or partially similar results (distance to the tributary, fish depth) can be explained by the limitations associated with each method. The results obtained with telemetry are very sensitive to the species composition and the size of the tagged fish. The number of fish located in the epibenthic areas of the reservoir can be underestimated by hydroacoustics. This preliminary case study highlights that these methods act in a complementary way and their simultaneous use can provide better information on fish spatial distribution.

International audience; Lakes in Europe are subject to multiple anthropogenic pressures, such as eutrophication, habitat degradation and alien species which are frequently inter-related. Therefore, effective assessment methods addressing multiple pressures are needed. In addition, these systems have to be harmonised (i.e. intercalibrated) to achieve common management objectives across Europe. Assessments of fish communities inform environmental policies on ecological conditions integrating the impacts of multiple pressures. However, the challenge is to ensure consistency in ecological assessments through time, across ecosystem types and across jurisdictional boundaries. To overcome the serious comparability issues between national assessment systems in Europe, a total anthropogenic pressure intensity (TAPI) index was developed as a weighed combination of most common pressures in European lakes that is validated against 10 national fish based water quality assessment systems using data from 556 lakes. Multi-pressure indices showed significantly higher correlations with fish indices than single-pressure indices. The best-performing index combines eutrophication, hydromorphological alterations and human use intensity of lakes. For specific lake types also biological pressures may constitute an important additional pressure. The best-performing index showed a strong correlation with eight fish-based national assessment systems. The developed best performing index can be used in lake management for assessing total anthropogenic pressure on lake ecosystems and creates a benchmark for comparison of fish assessments independent of fish community composition, size structure and fishing-gear. We argue that fish-based multiple-pressure assessment tools should be seen as complementary to single-pressure tools offering the major advantage of integrating direct and indirect effects of multiple pressures over large scales of space and time.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; International audience; The management of lakes requires the definition of physico-chemical thresholds to be used for ecosystem preservation or restoration. According to the European Water Framework Directive, the limits between physico-chemical quality classes must be set consistently with biological quality elements. One wayto dothis consists in analyzing the response of aquatic communitiesto environmental gradients across monitoring sites and in identifying ecological community thresholds, i.e. zones in the gradients where the species turnover is the highest. In this study, fish data from 196 lakes in France were considered to derive ecological thresholds using the multivariate method of gradient forest. The analysis was performed on 25 species and 36 environmental parameters. The results revealed the highest importance of maximal water temperature in the distribution offish species. Otherimportant parametersincluded geographical factors, dissolved organic carbon concentration and watertransparency, while nutrients appearedto havelowinfluence. In spite ofthe diversity of species responses to the gradients, community thresholds were detected in the gradients of the most important physico-chemical parameters and of total phosphorus and nitrate concentrations as well. The thresholds identifiedin such macroecological studymay highlight new patterns of species natural distribution andimprove niche characterization. Moreover, when factors that may be influenced by human activities are involved, the thresholds could be used to set environmental standards for lake preservation.; La gestion des plans d'eau nécessite la définition de seuils physico-chimiques pour la préservation ou la restauration des écosystèmes. Selon la Directive Cadre européenne sur l'Eau, les limites de classes de qualité physico-chimiques doivent être fixées en cohérence avec les éléments de qualité biologique.Une façon de faire consiste à analyser les réponses des communautés aquatiques aux gradients environnementaux formés par les sites de monitoring et d'identifier des seuils écologiques de communautés, c'est-à-dire des zones dans les gradients où le turnover des espèces est le plus important. Dans cette étude, les données de pêches provenant de 196 plans d'eau ont été considérées pour rechercher des seuils écologiques avec la méthode de gradient forest. L'analyse a porté sur 25 espèces avec 36 paramètres environnementaux. Les résultats ont révélé que la température maximale était le facteur le plus important dans la distribution des espèces de poissons. Les autres paramètres importants étaient les facteurs géographiques, la concentration en carbone organique dissous et la transparence de l'eau alors que les nutriments semblaient avoir peu d'influence. Malgré la diversité de réponses des espèces aux gradients, des seuils de communautés ont été détectés dans les gradients des paramètres physico-chimiques les plus importants ainsi que dans ceux des concentrations en phosphore total et en nitrates. Les seuils identifiés dans une telle étude macroécologique peuvent faire apparaître de nouveaux patrons de distribution naturelle des poissons et améliorer la caractérisation des niches spécifiques. De plus, quand des facteurs influencés par les activités humaines sont impliqués, ces seuils pourraient être utilisés pour fixer des limites pour la protection des plans d'eau.

International audience; In this study we developed a novel methodology based on fish communities to assess the ecological potential of central European reservoirs. Using the hindcasting approach, our index predicts values that could be observed in the absence of pressures for each reservoir depending on their environmental characteristics. Fish data were collected from 144 French and Czech reservoirs between 2005 and 2013 by standardized benthic gillnet sampling and transformed to functional and taxonomical metrics. After all validation by multiple testing of models redundancy and pressure-response, the final index was composed of three metrics: total biomass of fish, abundance of invertivores/piscivores, and abundance of planktivorous fish. The index accurately identifies reservoirs that are lightly, moderately and heavily affected by eutrophication. In addition to French and Czech reservoirs, this index could be a useful tool for countries with few reservoirs and the basis for further collaborative studies.

International audience; We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress

International audience; We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress

144ème réunion annuelle de l'American Fisheries Society, Québec, CAN, 17-/08/2014 - 21/08/2014; International audience; Acoustic fixed telemetry monitoring allows to track aquatic animals over large areas during long periods Pikeperch (Sander lucioperca), Pike (Esox lucius) and Perch (Perca fluviatilis), 3 piscivorous species, are often together in the European reservoirs. Our objective was to study the activity patterns of these species and temporal variability of the activity according to environmental parameters in order to better understand how they live together.The 3 piscivorous species have been monitored in a French reservoir (80 ha) with the VEMCO Positioning System (VPS-40 hydrophones) during two years (2012-2013). First the evaluation of the performances of the VPS system was assessed to get the main characteristics of our tracking system Then, the activity of 60 individuals has been described with two metrics, minimum moved distance (daily and hourly) and home range (daily and seasonal). During the day, the diel activity patterns of the 3 species were clearly different but a high variability was observed between individuals Moreover, activity patterns were different between seasons but all species were active in winter Finally, the metrics used to describe the activity were correlated positively with water temperature for perch and pikeperch, but not for pike

144ème réunion annuelle de l'American Fisheries Society, Québec, CAN, 17-/08/2014 - 21/08/2014; International audience; Acoustic fixed telemetry monitoring allows to track aquatic animals over large areas during long periods Pikeperch (Sander lucioperca), Pike (Esox lucius) and Perch (Perca fluviatilis), 3 piscivorous species, are often together in the European reservoirs. Our objective was to study the activity patterns of these species and temporal variability of the activity according to environmental parameters in order to better understand how they live together.The 3 piscivorous species have been monitored in a French reservoir (80 ha) with the VEMCO Positioning System (VPS-40 hydrophones) during two years (2012-2013). First the evaluation of the performances of the VPS system was assessed to get the main characteristics of our tracking system Then, the activity of 60 individuals has been described with two metrics, minimum moved distance (daily and hourly) and home range (daily and seasonal). During the day, the diel activity patterns of the 3 species were clearly different but a high variability was observed between individuals Moreover, activity patterns were different between seasons but all species were active in winter Finally, the metrics used to describe the activity were correlated positively with water temperature for perch and pikeperch, but not for pike

L'analyse des résultats de pêches d'échantillonnage effectués sur vingt lacs naturels français (altitude < 1 500 m) mettent en évidence trois assemblages piscicoles. Le schéma d'évolution générale des plans d'eau (vieillissement) permet d'y replacer ces groupes de poissons et de les valider d'un point de vue écologique. Ainsi, les lacs oligo- à oligo-mésotrophes de la zone péri-alpine se situent dans l'ichtyorégion à Corégones (Coregonus sp.), ou bien se caractérisent par l'assemblage Alburnus alburnus - Gobio gobio avec Salmo trutta et Phoxinus phoxinus. L'assemblage Esox lucius - Scardinius erythrophtalmus - Tinca tinca caractériserait les plans d'eau naturels mésotrophes, moins eutrophisés (ou moins turbides) que ceux où se trouve l'assemblage Stizostedion lucioperca - Gymnocephalus cernuus. Du fait de la capacité d'adaptation des poissons aux variations de leur environnement, ces assemblages ne sont pas strictement indicateurs d'une valeur d'indice trophique déterminée, mais permettent de préciser "l'état écologique" de l'ichtyofaune d'un lac, tel que le prévoit la directive cadre européenne sur l'eau. / Statistical analyses have been applied to the results of fish sampling operations on twenty French natural lakes (altitude < 1500 m); three fish assemblages were evidenced and placed inside the general evolution scheme of lakes. The oligo- and oligo-mésotrophic lakes can be characterized by Coregonids (inside a Coregonid ichtyo-region) or by the association of Alburnus alburnus - Gobio gobio, with the presence of Phoxinus phoxinus and Salmo trutta. Into mesotrophic lakes, the assemblage Esox lucius - Scardinius erythrophtalmus - Tinca tinca could be considered as typical, and is replaced by Stizostedion lucioperca - Gymnocephalus cernuus with large Cyprinids (Cyprinus carpio, Abramis brama) in eutrophic lakes. Because of the capacity of adaptation of the fish, these assemblages do not correspond narrowly to trophic quality indices but are indicators of the "ichtyological condition" of a lake, as requested by the European Water Frame Directive.