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

Environmental determinism of year to year recruitment variability of European eel in a small coastal catchment, the Frémur river, north-west France

The influence of environmental factors (mainly the river flow) on the year-to-year variability of European eel Anguilla anguilla fluvial recruitment in a small coastal River (north-west France) was examined. A comprehensive survey of catches from fixed traps at two weirs located at 4·5 km (Pont es Omnes Dam) and 6·0 km (Bois Joli Dam) above the river mouth was carried out between 1997 and 2004. Young pigmented elvers (mean ± s.d. total length, 133·7 ± 29·6 mm) were recruited in eel-passes from February to October, but the main runs followed a modal curve from April to September with a peak centred in May to June. Catches varied greatly between years, from 381 to 26 765 elvers. For each trap, a positive linear relationship between monthly mean river flow that preceded the maximal intensity of captures and annual total catches was observed. These relationships explained 73·1% (P <0.01) and 89·0% (P <0.001) of the year-to-year variability of the recruitment observed in the Pont es Omnes and Bois Joli traps respectively. A significant increase in river flow at the beginning of the migration peak would thus trigger a greater proportion of A. anguilla settled in the estuary and in the downstream zone of the Fremur River to begin their freshwater colonization. The physicochemical roles of changes in river discharge in stimulating upstream migration are discussed. It is concluded that fluvial recruitment in the Fremur River is mainly determined by environmental factors

Landscape and climatic characteristics associated with human alveolar echinococcosis in France, 1982 to 2007 , the FrancEchino network

International audience, the FrancEchino network. Landscape and climatic characteristics associated with human alveolar echinococcosis in France, 1982 to 2007. Euro Surveill. 2015;20(18):pii=21118. Available online: Human alveolar echinococcosis (AE) is a severe hepatic disease caused by Echinococcus multilocula-ris. In France, the definitive and intermediate hosts of E. multilocularis (foxes and rodents, respectively) have a broader geographical distribution than that of human AE. In this two-part study, we describe the link between AE incidence in France between 1982 and 2007 and climatic and landscape characteristics. National-level analysis demonstrated a dramatic increase in AE risk in areas with very cold winters and high annual rainfall levels. Notably, 52% (207/401) of cases resided in French communes (smallest French administrative level) with a mountain climate. The mountain climate communes displayed a 133-fold (95% CI: 95–191) increase in AE risk compared with communes in which the majority of the population resides. A case–control study performed in the most affected areas confirmed the link between AE risk and climatic factors. This arm of the study also revealed that populations residing in forest or pasture areas were at high risk of developing AE. We therefore hypothesised that snow-covered ground may facilitate predators to track their prey, thus increasing E. multilocularis biomass in foxes. Such climatic and landscape conditions could lead to an increased risk of developing AE among humans residing in nearby areas

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

Activité nycthémérale et utilisation de la séquence radier-profond par les truitelles d'un an (Salmo trutta L.)

Le comportement d'un groupe de dix truitelles d'un an (Salmo trutta L.) a été étudié au cours de deux cycles d'observation de 3 jours dans une séquence radier-profond reconstituée en milieu semi-naturel. Des changements de préférences d'habitat ont été mis en évidence à l'échelle du nycthémère et correspondent à des changements d'activité (repos, nage et alimentation). Lorsqu'elles sont en nage statique et en alimentation sur la dérive, les truitelles défendent leur poste et occupent le radier et le profond en pleine eau. Au repos, elles sont posées sur le fond du contre-courant et du profond, et elles n'exhibent pas de comportement agonistique. De plus, les truitelles ont montré un rythme d'activité diurne prononcé

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

Roles of discharge and temperature in recruitment of a cold-water fish, the European grayling Thymallus thymallus, near its southern range limit

Recruitment of salmonids is a result of density-dependent factors, specifically egg production in the previous year, and density-independent environmental processes driven by discharge and temperature. With the plethora of knowledge on major drivers of Atlantic salmon Salmo salar and brown trout Salmo trutta recruitment, there is a requirement to explore less known species, such as European grayling Thymallus thymallus, whose postemergence time coincides with period of increasing temperature and low discharge. This study assessed drivers of grayling recruitment in a southern English chalk stream, a system vulnerable to discharge and temperature alterations under future climate change predictions. The analyses explored age 0+ grayling survival in relation to conspecific and heterospecific densities and discharge- and temperature-derived factors. The final mixed-effects model revealed a positive relationship between age 0+ grayling survival and incubation temperature anomaly and age 0+ trout abundance. Similarly, postincubation temperature anomaly had a positive effect on 0+ grayling survival, but only up to a threshold temperature of 13.5°C, beyond which it had a negative effect. In contrast, increasing number of days with low discharge postincubation negatively influenced age 0+ grayling survival, with no evidence of an effect of elevated discharges following spawning. Our results emphasise the importance of maintaining natural discharge regimes in salmonid rivers by tackling multiple stressors operating at the catchment scale, including land and water use to mitigate for predicted climate driven changes. In addition, further research on recruitment drivers in less stable, rain-fed systems, is required