European Union legislation, through the Water Framework Directive (2000/60/ EC), as well as national legislation, such as the 'Grenelle Environnement ' (2007) in France, requires restoration of ecological connectivity in streams to improve free circulation of migratory fish. Different methods (e.g. capture by trap or net, telemetry, hydroacoustics) are used to evaluate the efficiency of fish passes to estimate the migratory species abundance and analyse changes in their within-river distributions. Among these methods, hydroacoustics is non-intrusive, allowing long-term observation and description of fish populations based on physical properties of sound in water. However, the main limit to hydroacoustic tools is their difficulty in identifying species. Initially designed for military purposes, dual-frequency identification sonar (DIDSON) has been used in environmental management for a decade. This acoustic camera uses higher frequencies and more sub-beams than common hydroacoustic tools, which improves image resolution and then enables observation of fish morphology and swimming behaviour. The ability to subtract static echoes from echograms and directly measure fish length improve the species-identification process. However, some limits have been identified, such as automatic dataset recording and the low range of the detection beam, which decreases accuracy, but efficient tools are now being developed to improve the accuracy of data recording (morphology, species identification, direction and speed). The new technological properties of acoustic cameras, such as the video-like visualization of the data, have greatly improved monitoring of diadromous fish populations (abundance, distribution and behaviour), helping river and fisheries managers and researchers in making decisions.

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Life history tactics of the brown trout (Salmo trutta) population of the Oir River (Normandy, France) were studied using passive integrated transponder (PIT) tagging data of five consecutive cohorts (5900 individuals) monitored between 1995 and 2002. Results demonstrate that (i) life history traits vary among cohorts, chiefly caused by environmental variability, (ii) juvenile growth, particularly second-year growth, plays an important role in the determination of the growing environment and trout exhibit variable migratory behaviour (from remaining in the natal brook to migrating in the sea) related to their juvenile growth rate, and (iii) the description of life history tactics (including juvenile growth, fine-scale migratory behaviour, and reproduction) can be clarified. Tactics are expressed along a continuum in time (age to reproduce) and space (distance of migration). Flexible life history tactics varying with juvenile growth is consistent with previous studies, but the use of empiric data on growth and migration from PIT tagging allows refining the description of life history tactics, taking into account their continuous distribution in time and space.Les tactiques d'histoire de vie de la population de truite commune (Salmo trutta) de l'Oir (Normandie, France) ont été étudiées par le marquage individuel à l'aide de « PIT tag » de cinq cohortes consécutives (5 900 individus) suivies de 1995 à 2002. Les résultats confirment et démontrent que (i) les traits d'histoire de vie varient entre les cohortes et que cette variabilité peut être reliée principalement aux fluctuations des conditions environnementales, (ii) la croissance juvénile, plus particulièrement celle de la seconde année de vie, est un facteur important dans la détermination de la zone de croissance et les truites possèdent des comportements migratoires variables, allant de la résidence stricte au ruisseau natal jusqu'à la migration en mer, que l'on peut relier à leur taux de croissance juvénile et (iii) la description des tactiques d'histoire de vie (en incluant la croissance juvénile, le comportement migratoire à fine échelle et la reproduction) peut être affinée, les tactiques se distribuant le long d'un continuum temporel (age de reproduction) et spatial (distance de migration). La flexibilité des tactiques d'histoire de vie et leurs liens avec la croissance juvéniles sont confirmés dans cette étude. Cependant l'utilisation de données empiriques sur la croissance et la migration issues du marquage individuel par PIT tag a permis d'améliorer la description des tactiques en prenant en compte leur distribution continue dans le temps et l'espace

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-Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their interactions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydrological exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic *Corresponding author: pierre.marmonier@univ-lyon1.frArticle published by EDP Sciences Ann. Limnol. -Int. J. Lim. 48 (2012) [253][254][255][256][257][258][259][260][261][262][263][264][265][266] Available online at: Ó EDP Sciences, 2012 www.limnology-journal.org DOI: 10.1051/limn/2012009 zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies.