Resolving the trade-off between silver eel escapement and hydropower generation with simple decision rules for turbine shutdown.

Hydropower plants are commonly reported as a major cause of the worldwide decline of freshwater eels (Anguillidae), so that management solutions are urgently needed to mitigate their impacts. Where downstream passage solutions are complex to develop, turbine shutdown appears as an effective management solution to protect silver eels during their river migration toward spawning areas. However, the definition of operational decision rules for turbine shutdown is challenging due to the duality between the benefit for eel conservation and the concomitant cost in term of hydropower production. Here, we proposed a decision framework for turbine shutdown based on simple hydrological criteria to guide negotiations between stakeholders toward a trade-off between silver eel escapement and hydropower generation. Eel migration was assumed to be triggered by a minimum river flow associated with a minimum discharge pulse, so that threshold values can be directly implemented as decision rules for turbine shutdown. To estimate relevant thresholds, a generic methodological framework was developed to generate alternative decision rules from data collected at hydropower plants, which can include telemetry surveys and estimates of eel abundance. A multiple-criteria decision analysis was then conducted to rank alternatives and to determine the best compromise between promoting silver eel escapement and limiting turbine shutdown duration. Graphic outputs can help stakeholders to understand the competitive interests between eel conservation and hydropower production, while visually identifying a range of consensual alternatives to support negotiations in the choice of operational thresholds. The method was illustrated for three river systems in Europe featured by distinct hydrological conditions and can be applied in other areas, providing that eel monitoring surveys and flow data are available.

Passage survival of European and American eels at Francis and propeller turbines.

We present the magnitude of losses of European eel Anguilla anguilla and American eel A. rostrata in passage through propeller and Francis turbines at hydroelectric projects. Survival and injury rates and types were turbine type related. Overall, eel survival was higher (mean ± 90% CI = 95.1 ± 5.3%,) and injury rate lower (12.5 ± 10.5) at Francis than propeller turbines (survival = 80.7 ± 6.4%; injury rate = 25.7 ± 7.9%). The common injury type at Francis turbines was bruises and at propeller turbines was severance. Blade shape and thickness of the leading edge of the blades (rounded, thick buckets of Francis turbines v. flatter, sharper edged blades in propeller turbines); eel entry routes into the turbines; their flexible, cylindrical body shape and orientation probably contributed to these differences. Relationship between survival and injury and turbine characteristics was turbine specific. For Francis turbines, one negative correlation (r = -0.986, P < 0.01) between survival and runner speed was found and two positive correlations between injury rates and fish length (r = 0.740, P < 0.10) and number of blades (r = 0.835, P < 0.05) were noted for propeller turbines. Several severely injured eels remained active 48 h after turbine passage suggesting caution is warranted when using telemetric movement for estimating eel survival. We conclude there is a need to (a) better understand travel paths and approach orientation of eels through turbines; (b) determine where only eel passage is of concern at hydropower plants that have both turbine types and therefore preferential operation of Francis turbines may be considered; (c) inform hydropower plant operators where turbine replacement is being considered and downstream eel passage is of concern that replacement by Francis or bulb turbines may prove beneficial for eel passage.

Differences in brain gene transcription profiles advocate for an important role of cognitive function in upstream migration and water obstacles crossing in European eel.

BACKGROUND: European eel is a panmictic species, whose decline has been recorded since the last 20 years. Among human-induced environmental factors of decline, the impact of water dams during species migration is questioned. The main issue of this study was to pinpoint phenotypic traits that predisposed glass eels to successful passage by water barriers. The approach of the study was individual-centred and without any a priori hypothesis on traits involved in the putative obstacles selective pressure. We analyzed the transcription level of 14,913 genes. RESULTS: Transcriptome analysis of three tissues (brain, liver and muscle) from individuals sampled on three successive forebays separated by water obstacles indicated different gene transcription profiles in brain between the two upstream forebays. No differences in gene transcription levels were observed in liver and muscle samples among segments. A total of 26 genes were differentially transcribed in brain. These genes encode for, among others, keratins, cytokeratins, calcium binding proteins (S100 family), cofilin, calmodulin, claudin and thy-1 membrane glycoprotein. The functional analysis of these genes highlighted a putative role of cytoskeletal dynamics and synaptic plasticity in fish upstream migration. CONCLUSION: Synaptic connections in brain are solicited while eels are climbing the obstacles with poorly designed fishways. Successful passage by such barriers can be related to spatial learning and spatial orientation abilities when fish is out of the water.

Automatic detection, identification and counting of anguilliform fish using in situ acoustic camera data: Development of a cross-camera morphological analysis approach.

Acoustic cameras are increasingly used in monitoring studies of diadromous fish populations, even though analyzing them is time-consuming. In complex in situ contexts, anguilliform fish may be especially difficult to identify automatically using acoustic camera data because the undulation of their body frequently results in fragmented targets. Our study aimed to develop a method based on a succession of computer vision techniques, in order to automatically detect, identify and count anguilliform fish using data from multiple models of acoustic cameras. Indeed, several models of cameras, owning specific technical characteristics, are used to monitor fish populations, causing major differences in the recorded data shapes and resolutions. The method was applied to two large datasets recorded at two distinct monitoring sites with populations of European eels with different length distributions. The method yielded promising results for large eels, with more than 75% of eels automatically identified successfully using datasets from ARIS and BlueView cameras. However, only 42% of eels shorter than 60 cm were detected, with the best model performances observed for detection ranges of 4-9 m. Although improvements are required to compensate for fish-length limitations, our cross-camera method is promising for automatically detecting and counting large eels in long-term monitoring studies in complex environments.

Towards transferability in fish migration models: A generic operational tool for predicting silver eel migration in rivers.

In the global context of river fragmentation, predicting fish migration is urgent to implement management actions aimed at protecting and promoting the free movement of diadromous fish. However, large-scale applicability of conservation measures requires transferable models that enable prediction of migration even in data-poor regions. Here, we surveyed 12 contrasted European river sites to predict the activity peaks of silver eels (Anguilla anguilla) during river migration towards spawning areas through an ensemble modelling approach. Site-specific Boosted Regression Tree (BRT) models were adjusted using standardized hydrological variables to predict migration probability, which were aggregated in consensus predictions. Results of independent cross-validations demonstrated that silver eel migration runs were accurately predicted in response to changes in river discharge. Transferability and predictive performance were improved by considering catchment-size dissimilarity between river sites (85 to 109,930 km2) when combining the site-specific predictions. Nevertheless, we provided two examples for which the effects of human actions on flow conditions were so high that they prevented reliable predictions of migration runs. Further contributions should thus take advantage of the flexibility of our approach for updating model collection with new sites to extend the predictive performance under a larger range of ecological conditions. Our transferable hydrological-based modelling framework offers an opportunity to implement large-scale management strategies for eel conservation, even in rivers where eel monitoring data lack. The BRT models and prediction functions were compiled in an R package named 'silvRpeak' to facilitate operational implementation by end-user managers, which can determine when mitigation measures should be implemented to improve river continuity (e.g. turbine shutdown and sluice gate opening) and balance their economic activity towards eel conservation. The only input required is discharge records that are widely available across European hydrological stations.

Evaluation of periodontal parameters on Removable Partial Denture abutment teeth with direct and indirect retainers: A 48-month follow-up.

OBJECTIVES: To evaluate periodontal parameters of abutment teeth and interproximal sites, in patients with mandibular class I Kennedy Removable Partial Dentures (RPD), after 4 years of periodontal treatment. METHODS: Fourteen patients with periodontal disease were treated and evaluated for the following parameters: plaque index (PI), bleeding on probing (BOP), probing depth (PD), gingival recession (GR), clinical attachment loss (CAL) and keratinized mucosa (KM). Parameters were compared between abutment teeth with direct and indirect retainers at all time-points. Periodontal maintenance was recorded at 6, 18 and 48 months. Data were analyzed using the Friedman and Wilcoxon Tests. RESULTS: Most patients (n=11; 78.6%) included were female and had a mean age of 66 years (± 7.8). After 48 months, a significant reduction was only observed in PI for both abutment teeth; in contrast, PD, GR, CAL and KM all increased by the end of the study. BOP increased at 48 months for the abutment teeth with direct retainers. The distal site of the abutment teeth with direct retainers presented higher values for GR and CAL. CONCLUSIONS: Non-surgical periodontal therapy was effective during the first 18 months, but periodontal conditions were worse at 48 months after therapy. The distal sites of abutment teeth with direct retainers presented the worst periodontal conditions.

A Practical Method for QTc Interval Measurement.

Objective The various formulae used for QT correction by heart rate (HR) require the execution of operations with the aid of calculators or applications. This study aimed to evaluate the performance of a simple rule for QTc estimation, comparing the measurements obtained with those provided by the commonly used equations of Bazett, Fridericia, Framingham, and Hodges. Methods We used the database of a previous observational study, which analyzed patients prospectively with acute pulmonary edema admitted in an emergency service. One hundred four patients were included for QTc assessment, of whom 86 patients underwent two ECG: one ECG <24h and other >24h after admission. Thus, a total of 190 ECGs were analyzed by two observers that manually measured QT and HR. QTc was obtained using the known formulae and the proposed equations: QTc = QT+2 (FC-60) for HR ≤ 90 bpm and QTc=QT+2(FC-60)-10 for HR>90 bpm. Results Bland-Altman plots show good agreement between the simple rule and Hodges equation, with a mean difference of -3,4, SD of 4.96 and 95% limits of agreement from -9,9 to 3.2. There was not a good agreement between the simple method and the other formulae. Conclusion The proposed method has good agreement with the measures of QTc by the equation of Hodges in the HR range of 40 to 130bpm in acutely ill patients. Our method may be a plausible option for quick QT correction in these subjects.

Adult Atlantic salmon have a new freshwater predator.

The Atlantic salmon (Salmo salar) is one of the world's most emblematic freshwater fish. Despite conservation and rehabilitation plans, populations of this species are dramatically declining due to human impacts such as habitat fragmentation, overfishing and water pollution. Owing to their large body size, anadromous adults were historically invulnerable to fish predation during their spawning period migration. This invulnerability has disappeared in Western Europe with the introduction of a new freshwater predator, the European catfish (Silurus glanis). Here we report how adults of Atlantic salmon are predated in the fishway of a large river of SW France, where the delayed and narrow passage created by the structure increases the probability of predator-prey encounter. We assessed predation risk by monitoring salmon and catfish in one fishway of the River Garonne, using video fish-counting from 1993 to 2016. We analysed the predation strategy of catfish using observations made with acoustic camera and RFID telemetry in 2016. Our results demonstrate a high predation rate (35%-14/39 ind.) on salmon inside the fishway during the 2016 spawning period migration. Our results suggest that a few specialized catfish individuals adapted their hunting behaviour to such prey, including their presence synchronized with that of salmon (i.e, more occurrences by the end of the day). Such results suggest that the spread of European catfish will potentially impact migration of anadromous species through anthropized systems.