What do we know to evaluate the health of brown trout (Salmo trutta) populations?

peer reviewedThe renewed emphasis on the concept of the health of ecosystems highlights society’s interest in taking measures to protect environments transformed by human activity. The criteria used for evaluating the health of fish population are rarely discussed within the scientific community. The exercise proposed here aimed to discuss these for the brown trout (Salmo trutta), a flagship species from the freshwater fish community typical from headwaters of watercourses which represent most of the French hydrographic network. This initiative aimed to gather the ideas of a limited number of experts on the function of these populations and on the criteria for evaluating their function. The main key parameters were identified and organised into a hierarchical framework for each development stage. A consensus emerged on the fact that in the current stage of knowledge, the diagnosis can be established based on the analysis of abiotic parameters crucial for the biology and, with more difficulty, on the analysis of biotic parameters. For all the development stages, the identified parameters are linked to habitat (substrate, stream flow, temperature and water quality), hydrology and connectivity. Further knowledge must be acquired in order to be able to measure the biological criteria. That implies to reinforce longterm biological monitoring and research to understand the variability in biological parameters, the relevant spatiotemporal scales and the functional processes

Déterminisme environnemental du sexe chez l'Anguille Européenne Anguilla anguilla.

Contrairement à la majorité des mammifères, la plupart des poissons ne possèdent pas de chromosomes sexuels hétéromorphes (type XY/XX). Chez un grand nombre de poisson la labilité du sexe est extrêmement prononcée. Cela se traduit par le fait que le déterminisme du sexe peut être sous l influence de variables environnementales. C est le cas chez l anguille où la proportion de mâle augmente avec le nombre d individus présents en un lieu donné. Cette thèse a pour but de mieux comprendre les facteurs qui régissent la destiné sexuelle des individus. Ainsi, les relations inter-individuelles et la croissance ont été étudiées afin d évaluer leur possible rôle dans le déterminisme du sexe. Les résultats acquis au cours de cette thèse suggèrent que la densité per se ne serait pas le facteur primordial influençant le déterminisme du sexe, mais plutôt l estimation faite par les individus de la qualité du milieu.Contrarily to most mammals, the majority of fish doesn t have heteromorphic sexual chromosomes (type XY/XX). In most fish, the gonad development is extremely labile and for some of them, the sex can be influenced/determined by environmental factors. This is observed in eel, where the proportion of males increases with the number of individuals at a given location. The goal of this thesis is to better understand processes that act upon sex determination in eel. Thus, inter-individual relationships as well as the growing potential of each fish were studied to evaluate their possible role in sex determination. The findings gathered throughout this thesis support the hypothesis of a metagametic (environmental) sex determination and also suggests that the estimation of the quality of the environment, made by juveniles eels, is one of the key factors influencing sex determination.PAU-BU Sciences (644452103) / SudocSudocFranceF

A permeable hyporheic zone may contribute to buffer the effects of a drying event on prey availability for salmonid juveniles

Climate change is increasing the intensity and frequency of hydrological events in freshwater. Summer droughts and drying events drastically reduce the favourable habitat for aquatic organisms shaping interactions among species. Macroinvertebrates are usually less abundant during severe summer low flows, reducing prey availability for carnivorous fish, such as brown trout (Salmo trutta). To quantify the consequences of a surface water drying event on fish performance, we conducted an experiment in 6 experimental channels naturally fed by water and macroinvertebrates. After a colonisation period for macroinvertebrates, the water level was dropped to the benthic surface for two weeks in 3 channels, while it remained constant in the 3 other channels. After water level restoration, juvenile brown trout were reared for three weeks in the control and dry channels. The drying event did not reduce the abundance of macroinvertebrates. Survival and growth of juvenile trout were unaffected by drying. Our experiment provided circumstantial evidence that the hyporheic zone could potentially serve as an effective refuge for macroinvertebrates, mitigating the effects of drying events on food webs, although this mitigation would strongly depend on sediment characteristics, habitat quality and the composition of the macroinvertebrate community

Influence of Daily Variations of Light and Temperature on the Emergence Rhythm of Grayling Fry (<i>Thymallus thymallus</i>)

The emergence rhythm of grayling fry (Thymallus thymallus) was studied in four aquaria fitted with traps under four different conditions of light and temperature. Both light and temperature induced an emergence rhythm characterized by a 24-h period. Under ambient Sight and constant temperature, emergence peaked at the end of the night before the onset of dawn. Under constant dim light and varying temperature, emergence peaked in early morning during the coldest hours. When both light and temperature fluctuated daily the emergence pattern was equivalent to the "sum" of these previous two regimes and was similar to that described in the field in a previous report. In the absence of light and temperature variations, no emergence rhythm was observed. </jats:p

Freshwater habitat of Atlantic salmon (<i>Salmo salar</i>)

This perspective summarizes our knowledge of the freshwater habitat of Atlantic salmon (Salmo salar). The article is organized by life stage and identifies areas where more research is needed. For example, little is known of the kelt and presmolt life stages despite their importance in stock maintenance. We also believe that further investigation is required to assess the relevance of variables currently used to characterize habitat and that more attention should be focussed on adult and embryo-larva habitat requirements. We also discuss the fact that the majority of research is directed at habitat at the micro (i.e., immediate area around the fish) and macro scales (area of the geomorphological unit), while the influence of habitat at higher spatial scales should also be considered. </jats:p

Video tracking in the extreme: a new possibility for tracking nocturnal underwater transparent animals with fluorescent elastomer tags

Initially developed so that an individual could be recognised in mark-recapture studies of aquatic animals, fluorescent VIE (Visible Implant Elastomer) tags are used here for a new application in ethometry: the study of behavior of transparent animals in dim light or in darkness using automatic tracking technology. The application and validation of this multitracking method is tested in the context of research on the glass eel (Anguilla anguilla) estuarine migratory behavior, a crucial point to better understand the dynamics of this endangered species. The method makes it possible to measure the activity (notably distance and speed) of four individuals as a function of tidal and nycthemeral rhythms in the same flume (circular aquarium simulating the river or estuarine conditions) across a wide time scale (from seconds to weeks)

Data from: Genetic architecture of threshold reaction norms for male alternative reproductive tactics in Atlantic salmon (Salmo salar L.)

Alternative mating tactics have important ecological and evolutionary implications and are determined by complex interactions between environmental and genetic factors. Here, we study the genetic effect and architecture of the variability in reproductive tactics among Atlantic salmon males which can either mature sexually early in life in freshwater or more commonly only after completing a migration at sea. We applied the latent environmental threshold model (LETM), which provides a conceptual framework linking individual status to a threshold controlling the decision to develop alternative traits, in an innovative experimental design using a semi-natural river which allowed for ecologically relevant phenotypic expression. Early male parr maturation rates varied greatly across families (10 to 93%) which translated into 90% [64–100%] of the phenotypic variation explained by genetic variation. Three significant QTLs were found for the maturation status, however only one collocated with a highly significant QTL explaining 20.6% of the variability of the maturation threshold located on chromosome 25 and encompassing a locus previously shown to be linked to sea age at maturity in anadromous Atlantic salmon. These results provide new empirical illustration of the relevance of the LETM for a better understanding of alternative mating tactics evolution in natural populations

Glass eel swimming behaviour during their estuarine migration: new insights from video tracking analysis

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