Background: Recent improvements in fixed acoustic monitoring receivers allow the tracking of individual aquatic animals over long periods of time with regular fine-scale positions. The VEMCO Positioning System (VPS) is now widely used, but various methodological issues remain to be clarified. The aim of this study was to analyze the spatial distribution of the probability of location and the positioning error over the entire surface of a hydropower reservoir, prior to analyzing fish behavior. Findings: Filtering the data set by the horizontal position error (HPE) significantly reduced the positioning error. Retaining only the positions with an HPE less than 15 retained 79% of VPS positions and decreased the positioning error by 33% (mean = 3.3 m, SD = 3.3 m). A higher probability of location was observed inside than outside the receiver array (44% and 36%, respectively). Moreover, the positioning error significantly differed inside (n = 243, mean = 2.4 m, SD = 2.1 m) and outside (n = 253, mean = 4.2 m, SD = 4.0 m) the receiver array (P < 0.001). Finally, the lowest positioning errors were detected in the area with the highest receiver density. Conclusions: The VPS measures fish positioning in a reservoir, under suitable conditions, with satisfactory accuracy. We showed that the probability of location and the positioning error differed spatially in accordance with previous results in other conditions. Consequently, these analyses are recommended as a prerequisite to further spatial analyses using VPS-derived data.
The effects of industrial cooling water on fish communities were widely debated at the end of the seventies, when large thermal power plants were being developed. This led to numerous research programs on thermal tolerance in fish. The recent warming climatic period and especially the 2003 heat wave have brought thermal biology back to center stage. The work presented here has consisted in analyzing historical and contemporary literature to update basic knowledge on thermal tolerances of 19 riverine fish species. These data were then validated and completed by European fish specialists. We finally proposed a synthesis, based on more than 300 references, which details thermal tolerances for the entire life cycle: reproduction, embryonic, larval, juvenile and adult life stages. This updated material is of great importance to an understanding of the trends observed in fish communities or for forecasting future behavior in climate change scenarios. RÉSUMÉSynthèse des tolérances thermiques des espèces de poissons communes des rivières et fleuves de plaine de l'ouest européen L'effet de l'élévation de température des cours d'eau a été largement débattu à la fin des années 70 qui ont connu le développement des centrales thermiques de grande puissance. Ces études ont généré alors de nombreux programmes de recherche sur la tolérance thermique des poissons, dont les résultats sont parfois oubliés ou difficiles à rassembler. Le réchauffement climatique actuel et en particulier l'épisode caniculaire de 2003 a mis de nouveau ce thème sur le devant de la scène. Le travail de synthèse présenté a consisté à analyser des données historiques et contemporaines de la littérature, afin de mettre à jour les connaissances de base sur les tolérances thermiques de 19 espèces de poissons d'eau douce. Cette synthèse a ensuite été validée et complétée par des spécialistes européens. Elle s'est appuyée sur plus de 300 références qui détaillent les tolérances thermiques de chacun des stades du cycle de vie des espèces étudiées : reproduction et stades embryonnaire, larvaire, juvénile et adulte. Cette mise à jour est essentielle pour comprendre les tendances d'évolution déjà constatées des communautés de poissons et prévoir les futures évolutions en fonction de différents scénarios de changement climatique.
Water-level fluctuations are a major function of reservoirs that influence the littoral zone of the lake, and prove to be of high importance for the whole biological communities of lakes. Working on a French hydropower reservoir, we studied the influence of water-level fluctuations on intra-annual variations of littoral habitat availability and their consequences for the structure of fish assemblages inhabiting the littoral zone. As the water level decreased significantly, habitat conditions tended to be much more homogeneous. The proportion of sites with a thin substrate and low slope increased, while submerged vegetation and riparian shade disappeared. The relationship between habitat complexity and fish assemblage changed along the water-level gradient. The habitat effect on assemblage structure was strongest when the water-level conditions were high and very high, and weaker for low and very low water-level conditions. A homogenization of fish assemblages was observed when the water-level condition reached a threshold. These results suggest an effect of water-level management in structuring fish assemblages of the littoral zone of a reservoir due to a decrease of habitat complexity.
Despite the many habitat simulations that have been undertaken around the world, not enough biological monitoring has been performed following flow manipulations. It is difficult, however, to refine flow management decisions without a better understanding of the links between amounts, durations and seasonality of flow deliveries and population dynamics.Trout populations were monitored before and after flow alterations in five trout streams, involving 17 study sites over a 4-to 12-year period, depending on the sites.A comparison of the trout populations observed to theoretical habitat/population models pointed up several helpful lessons. Various factors slow increases in population size, including the availability and quality of spawning grounds, the general connectivity of the bypass section (BPS) and severe spate events. In addition to these site-dependent factors, hydrological dynamics may explain why it is so difficult to clearly identify relationships between habitat availability and real fish stocks. Moreover, opportunities to observe population changes are improved when the pre-enhancement instream flow value is very low, and when there is a considerable difference between pre-and post-enhancement values. A population dynamics model that incorporates different habitat limitations and demographic background can be a very precious tool to improve understanding of the different situations and to build scenarios of population recovery.
Changes in a brown trout (Salmo trutta L.) population result from interaction among various mechanisms which are dependent on environmental conditions and biotic processes. In reaches influenced by the presence of dams, the instream flow in the bypassed section is not the only parameter which affects the population. Flood episodes, the general connectivity of the bypassed section, and the characteristics of the substrate which define the availability and quality of spawning grounds may also have a crucial impact. The design and fine-tuning of tools which take environmental parameters into account can improve our understanding of the dynamics of such influenced populations. In this perspective, a deterministic model (MODYPOP) has been developed in an attempt to integrate all these factors and to test the effect of different long-term scenarios of influenced flow regimes on the structure of trout populations. MODYPOP was applied to three populations and three reaches (on the Roizonne, Neste d'Aure and Lignon du Forez rivers in France). For each stream, experiments were carried out on a bypassed section downstream of a hydropower station, before and after an increase in the minimum instream flow due to relicensing. These experiments allowed integrating into MODYPOP local phenomena (impact of flood episodes, impact of flushing, impact of downstream migration of juveniles and adults) affecting the populations during the study period and then calibrating them. To estimate the change in the population due to the increase in minimum instream flow, different long-term simulations were run, selecting discharge patterns at random. These scenarios help to evaluate the time required for the population to return to a range close to habitat saturation after an improvement in the hydraulic habitat or following a flood event. These applications have enabled determining the relative importance of changes in population density due to different types of events.
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