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[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Perch Perca fluviatilis is a widespread predator in European reservoirs, frequent in open waters but also known to spend a lot of time in the littoral zones. To get insight into how adult perch used and selected their habitat in an environment subject to water level fluctuations, 21 perch were continuously tracked using acoustic telemetry over 2 years in the Bariousses reservoir (France). The different available habitats were characterized by depth classes and substrate types, presence of emerging trees, and presence of tree stumps in the littoral zone. We showed that perch habitat preferences were strongly dependent on the season, except for substrate type, and in line with their habitat use. Surprisingly we did not find any influence of the water level which however reduced the structural complexity of the littoral zone when lowering. In spring and summer, whatever the water level, we observed a strong preference for the littoral zone and complex habitats. In autumn and winter, perch migrated into deeper waters. However, the individual variability of the habitat preferences was quite high. This type of research helps to understand the spatial ecology of fish and provides useful guidance to hydromorphological restoration for fish populations.

[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

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE; International audience; Global biodiversity in freshwater and the oceans is declining at high rates. Reliable tools for assessing and monitoring aquatic biodiversity, especially for rare and secretive species, are important for efficient and timely management. Recent advances in DNA sequencing have provided a new tool for species detection from DNA present in the environment. In this study, we tested whether an environmental DNA (eDNA) metabarcoding approach, using water samples, can be used for addressing significant questions in ecology and conservation. Two key aquatic vertebrate groups were targeted: amphibians and bony fish. The reliability of this method was cautiously validated in silico, invitro and insitu. When compared with traditional surveys or historical data, eDNA metabarcoding showed a much better detection probability overall. For amphibians, the detection probability with eDNA metabarcoding was 0.97 (CI=0.90-0.99) vs. 0.58 (CI=0.50-0.63) for traditional surveys. For fish, in 89% of the studied sites, the number of taxa detected using the eDNA metabarcoding approach was higher or identical to the number detected using traditional methods. We argue that the proposed DNA-based approach has the potential to become the next-generation tool for ecological studies and standardized biodiversity monitoring in a wide range of aquatic ecosystems. see also the Perspective by Hoffmann, Schubert and Calvignac-Spencer.

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

La diversité des écosystèmes lacustres s’explique en partie par la variété hydromorphologique des lacs ; la nature et la répartition du substrat qui tapisse leur fond sont des composantes de ce paramètre. C’est pour cela que la Directive Cadre sur l’Eau impose une description de la nature des sédiments des plans d’eau. Plus généralement, la répartition des substrats peut être considérée comme un facteur de structuration des espèces biologiques qu’abrite un lac. Des outils traditionnels comme l’utilisation d’une benne à sédiment ou d’une caméra subaquatique permettent de déterminer la nature des substrats de manière très ponctuelle mais ces techniques atteignent leurs limites lorsque tout un plan d’eau doit être caractérisé. Depuis les années 1980 des méthodes de caractérisation des sédiments utilisant des outils acoustiques qui permettent d’obtenir des informations en continu le long de parcours réalisés par un navire ont été développées et commercialisées. Pour l’application aux écosystèmes lacustres, de part leur mise en oeuvre, les systèmes utilisant les échosondeurs mono‐faisceau paraissent les plus appropriés. Ces appareils permettent de réaliser des cartes de la répartition des substrats à l’échelle du lac. Les informations pertinentes qui permettent de décrire un état biologique potentiel ou de définir un état initial peuvent être ainsi intégrer dans la mise en place des réseaux de suivi de la qualité des milieux. / The lake ecosystem diversity is explained, in part, by the hydromorphological diversity of lakes; nature and repartition of the substrata give information about this parameter. That is the reason why the European Water Framework imposes a substrata nature description of lakes. The substrata repartition could be considered as a factor of the biological structuring presents in lakes. Traditional tools like grab samplers or video cameras enable to determine the substrata nature but they are not appropriate for getting a high resolution description for an entire lake. From the beginning of the 80’s, acoustic devices specialized in seabed classification have been developed and commercialized. For lakebed surveys, systems using single beam sounders seem to be more appropriate; they enable to obtain maps of the lakebed at the whole lake scale. Information which describes a potential biological state can be used for the establishment of a quality monitoring.

National audience; Pour décrire l'état écologique des plans d'eau, la DCE (Directive Cadre sur l'Eau) impose la connaissance de leur état hydro-morphologique et notamment la description de la nature des substrats. Plusieurs outils acoustiques ont été développés depuis les années 1980 permettant de faire de la classification de la nature des fonds subaquatiques tel que les sidescan sonars, les sondeurs multi faisceaux et les échosondeurs mono faisceau. Ces techniques acoustiques permettent de mieux prendre en compte la dimension spatiale que les méthodes traditionnelles (caméra, bennes à sédiments,). En milieu lacustre, l'utilisation d'un échosondeur parait plus adapté (du point de vue des surfaces à échantillonner) et moins coûteux que les autres technologies. Sonar5-pro, logiciel d'analyse des signaux issus d'échosondeurs et spécialisé dans le calcul de biomasse de poissons, vient d'implémenter un module mettant à disposition les données qui permettent d'appliquer une méthode classique de détermination de la nature des fonds à partir de signaux acoustiques. Nous avons testé la faisabilité de la classification de la nature des fonds lacustres en utilisant ce module. Une première phase de détermination des paramètres d'acquisitions optimaux de l'onde émise par l'échosondeur a été réalisée. La base de données de référence nécessaire à la classification a ensuite été construite par vérification in situ de la nature des substrats. Le système a été utilisé dans le Léman pour établir une cartographie de la nature des substrats d'une omblière, zone de fraie de l'omble chevalier (Salvelinus alpinus). Les observations sur l'évolution temporelle des substrats de cette zone pourraient être mises en regard de la dynamique de l'espèce et de la nécessité de restaurer de telles zone

The objectives of this paper are to describe the fish assemblages in French reservoirs and to relate them to the sites' characteristics. The results of 43 fishing surveys were collected and completed with environmental descriptors. Fish assemblages differ between salmonids-dominated mountain sites and lowland ones. The latter show higher species diversity and a distinction between rheophilic- and limnophilic-type communities. This distinction can be explained by the reservoir age, location in the catchment and depth. The response of fish communities to these variables was investigated by canonical correspondence analysis. It shows that rheophilic species are typically abundant in upper basin, deep and recently created reservoirs. The fish community response to the aging process corresponds to an addition of lowland standing waters species and an extinction of the native riverine ones. The structuring role of the sites' depth, location and age is discussed, considering their relationship with the water body trophic status.

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.

The impacts of environmental factors on fish biological functions are well documented but the consequences of these relationships on population dynamics in natural hydrosystems are rarely assessed. We first studied the co-variations in the year-class strength (YCS) indices of the pikeperch (Sander lucioperca L.) and the perch (Perca fluviatilis L.) in a hydro-electric reservoir located in central France. Then, we analysed the relationship between the meteorological conditions during and after the spawning period, the water level fluctuations, and the YCS of these species. No co-variation was observed between the YCS of the two Percids. No significant relationship was measured between the reservoir level changes, the meteorological conditions and the pikeperch population dynamics. The summer temperature post spawning is the only variable positively correlated with the perch YCS. Our results suggest distinct regulation processes between the YCS of the perch and the pikeperch, L`impact des facteurs environnementaux sur les fonctions biologiques sont généralement bien décrits mais les conséquences en terme de dynamique des populations sont rarement évaluées. Nous avons étudié les co-variations de la force des cohortes (YCS) de sandre et de perche dans la retenue d`Eguzon (36). Ensuite nous avons analysés les relations entre les forces des cohortes et (i) les fluctuations du niveau d`eau, (ii) les conditions méteorologiques en période de ponte et (iii) les températures estivales et hivernales post-ponte. Aucune co-variation des YCS n`est observée. De plus aucun effet significatif du marnage n`est mesuré sur les YCS de ces espèces. Parmi les variables météorologiques, seule la température estivale est positivement corrélée à la YCS de la perche. Nos résultats suggèrent, pour ces deux Percidés, l`existance de différents processus de régulation de la dynamique des populations.