Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in... more Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the physical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations (Ance du Nord and Oriège). Application of this methodology to hydropeaking conditions requires additional habitat descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; hydropeaking effects on habitat parameters are different in wide and in deep profiles. It is suggested that, in both instances, hydraulic refugia are crucial for organisms to withstand the v...
... on Guar-anteed Flow that groups experts from different research bodies, gov-ernment agencie... more ... on Guar-anteed Flow that groups experts from different research bodies, gov-ernment agencies and Electricité de France (Merle and Eon ... carrying capacity and the occupancy rates remain very low in comparison with both the reference reach and averages for French rivers. ...
... Particularly, the flow-related habitat role simulated in the model – through a phenomenon of ... more ... Particularly, the flow-related habitat role simulated in the model – through a phenomenon of compensation during the first months of life and through displacement resulting in mortality, and mortality among fry when discharge is high – was illustrated by these examples. ...
Changes in a brown trout (Salmo trutta L.) population result from interaction among various mecha... more 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.
Despite the many habitat simulations that have been undertaken around the world, not enough biolo... more 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.
It is often difficult to determine the real impact on downstream fish populations of a change in ... more It is often difficult to determine the real impact on downstream fish populations of a change in the mode of management of a hydropower installation and, in particular, the impact of an increase in the instream minimum flow. Other factors in addition to the simple limitation of habitat in low-flow periods can influence the evolution of a fish population over time. It was often observed that the 0+ individuals appear limited by strong discharge in the first months after their emergence (March to May). In an attempt to provide some answers, a dynamic model of a trout population (MODYPOP) has been applied to the river Roizonne in the French Alps upstream and downstream of a hydropower station, in order to estimate the effect of different discharge time series on trout population dynamics. The trout populations were monitored by means of annual inventories at two study sites -one with minimum flow and the other with natural flow. At each site, the available habitat was described and simulated as it changed with the discharge, according to the "microhabitat" method (EVHA, derived from PHABSIM). Habitat time series were built on the basis of discharge time series. The MODYPOP simulations, integrating habitat and discharge time series, were compared with observed numbers of fish; the results indicate that fluctuations in discharge during the post-emergence period play a major role in the dynamics of the total population. Predictions can be significantly improved if the impact of strong discharge on emerging fry is integrated in the model.
The conclusions of numerous stream restoration assessments all around the world are extremely cle... more The conclusions of numerous stream restoration assessments all around the world are extremely clear and convergent: there has been insufficient appropriate monitoring to improve general knowledge and expertise. In the specialized field of instream flow alterations, we consider that there are several opportunities comparable to full-size experiments. Hundreds of water management decisions related to instream flow releases have been made by government agencies, native peoples, and non-governmental organizations around the world. These decisions are based on different methods and assumptions and many flow regimes have been adopted by formal or informal rules and regulations. Although, there have been significant advances in analytical capabilities, there has been very little validation monitoring of actual outcomes or research related to the response of aquatic dependent species to new flow regimes. In order to be able to detect these kinds of responses and to better guide decision, a general design template is proposed. The main steps of this template are described and discussed, in terms of objectives, hypotheses, variables, time scale, data management, and information, in the spirit of adaptive management. The adoption of such a framework is not always easy, due to differing interests of actors for the results, regarding the duration of monitoring, nature of funding and differential timetables between facilities managers and technicians. Nevertheless, implementation of such a framework could help researchers and practitioners to coordinate and federate their efforts to improve the general knowledge of the links between the habitat dynamics and biological aquatic responses.
... The need today to adopt multi-use management strategies for rivers requires that ... WUA chro... more ... The need today to adopt multi-use management strategies for rivers requires that ... WUA chronologies were reconstituted using available chronologies of discharge from 1988 to 1998 for ... Monitoring of the populations present (fecundity, growth, etc.) and knowledge of the habitat ...
The Orlu hydroelectric power plant on the River Orikge is managed by 'hydropeaking' and generates... more The Orlu hydroelectric power plant on the River Orikge is managed by 'hydropeaking' and generates significant and frequent daily fluctuations in flow downstream. Observations at this site aimed to determine the impact of these variations on the aquatic environment. Surveys were carried out in June and October, upstream and about 2 km downstream of the plant, with a view to studying fish feeding habits and nutritive resources. In June, when the natural river flow was high, invertebrate populations differed very little between the two sectors. In October, after the low-water period, density and biomass were significantly lower in the downstream sector than they were upstream. Invertebrate drift was studied by taking samples every hour over a 24-hour cycle. Upstream, this drift showed a clear daily rhythm, dominated by nocturnal drift. Downstream in June, invertebrate drift was more abundant than upstream; a similar nychthemeral rhythm was apparent, but there were significant peaks during hydropeaking. In October, this daily rhythm disappeared, and drift was extremely low when river flow was low; on the other hand, a marked increase was observed during hydropeaking. Fish feeding habits were studied parallel to drift by capturing about 20 fish every four hours and analysing their stomach contents. No clear rhythm in the daily food uptake was observed. Stomach content was more abundant downstream. Lastly, the number of prey captured by fish at a given period of the day did not appear to be linked with the effective quantity of invertebrates simultaneously available in the river.
... aim of this paper is to illuminate any environmental preference of brown trout (Sulma tritttu... more ... aim of this paper is to illuminate any environmental preference of brown trout (Sulma tritttu, fario) in streams of the South of France and, in ... The presence of fish was checked by using two special electric fishing techniques: (1) casting the anode ahead of the operator for a sudden ...
Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in... more Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the physical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations (Ance du Nord and Orikge). Application of this methodology to hydropeaking conditions requires additional habitat descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; hydropeaking effects on habitat parameters are different in wide and in deep profiles. It is suggested that, in both instances, hydraulic refugia are crucial for organisms to withstand the variations of physical variables. This approach helps in better understanding the physical limiting factors in situations of short-term flow fluctuations.
Bulletin Français de la Pêche et de la Pisciculture, 1993
ABSTRACT L'objectif est de quantifier le rôle des abris et caches des rivières aménagées ... more ABSTRACT L'objectif est de quantifier le rôle des abris et caches des rivières aménagées sur le peuplement des truites fario. L'étude s'est déroulée sur deux tronçons de cours d'eau pyrénéens : la PIQUE (altitude 920 m NGF) et le GER (altitude 390 m NGF), situés dans le département de la Haute-Garonne (31). Pour les caches naturelles, nous avons expérimenté sur trois ensembles qui ont pu être transitoirement condamnés par des grillages : enrochement des berges, caves creusées sous les berges, et branchages. Ceci a pu être réalisé sur le GER. Initialement, le secteur (avec tous ces types de caches) possède une densité moyenne de 2469 ind/ha pour une biomasse de 278 kg/ha. Quand l'accès aux caches est condamné, la densité se stabilise à 1000 ind/ha pour une biomasse d'environ 125 kg/ha, soit une diminution de l'ordre de 55 % en densité et en biomasse. Suivant les types de caches, la recolonisation, après 21 jours de réouverture des caches, est estimée entre 28 et 72 % pour la biomasse et entre 42 et 62 % pour la densité. Pour les caches artificielles, six types de matériaux de construction (brique, tuile...) ont été expérimentés sur un tronçon de la PIQUE (dénudé de toute cache naturelle). Suivant les types de caches et leur disposition, la densité des truites varie de 3 à 23 ind/m2 de cache, et de 0,09 à 0,2 ind/m2 hors cache. Parmi les matériaux utilisés, on observe une nette préférence pour les briques et, selon les dispositions testées, les meilleurs résultats sont obtenus avec les caches placées soit près, des rives, soit dans la totalité du lit. L'expérience a montré le rôle prépondérant des caches naturelles et artificielles sur le peuplement des truites dans un cours d'eau aménagé. The aim of this study was to quantify the role of various cover types and examine their selection by brown trout. The study was developed on two river course sections in the Pyrenees : the river PIQUE (altitude 920 m NGF) and the river GER (altitude 390 m NGF), situated in the department of the Haute-Garonne (31). For the natural cover, we have experimented on three sets which have been transitionnally blocked by wire netting ; rocky river bank, undercut bank and woody debris. This has been performed on the river GER. Initially, the sector, for ail these types of covers, had an average density of 2469 ind/ha for a biomass of 278 kg/ha. When the access to the covers is protected, the density stabilises to 1000 ind/ha, being a decrease in the order of 55% in density and biomass. According to the type of cover, the recolonisation, after 21 days of reopening of the covers, is estimated between 28 and 72% for the biomass and between 42 and 62% for the density. For the artificial covers, six types of building materials (brick, tile...) have been experimented on the river PIQUE section (ail natural covers having been removed). By type of covers and their location, the trout density varied from 3 to 23 ind/m2 of cover, and from 0.09 to 0.2 ind/m2 outside cover. Among the material used, we observed a clear preference for brick and, depending on the dispositions tested, the best results have been obtained with the covers placed near the banks, or being in the totality of the bed. The experiment has shown the major rôle the natural and artificial covers have on trout populations.
Bulletin Français de la Pêche et de la Pisciculture, 1998
ABSTRACT Afin d'évaluer l'impact des différents usages de l'eau sur l&... more ABSTRACT Afin d'évaluer l'impact des différents usages de l'eau sur l'écosystème aquatique, des outils de simulation de plus en plus nombreux voient actuellement le jour ; dans ce cadre, un modèle de dynamique de population de truite (Salmo trutta) est en cours de développement. Pour enrichir les nombreuses observations déjà disponibles sur le bassin de l'Oir (Basse-Normandie), des inventaires assortis d'expérimentations spécifiques ont été effectués en 1996 pour conforter et compléter les différentes composantes du modèle, en particulier en ce qui concerne les fonctions biologiques impliquées. En particulier, l'étude de l'habitat permet de déterminer la capacité d'accueil du milieu et ainsi une composante densité-dépendante de la survie des jeunes truitelles ; le potentiel reproducteur est appréhendé à l'aide de prélèvements sanguins et du sacrifice de quelques femelles matures. D'éventuels échanges avec l'aval du bassin sont quantifiés à l'aide d'un système de piégeage. Les résultats de ces expérimentations permettent d'effectuer une première application sur l'ensemble du bassin et de comparer les simulations obtenues aux données issues des inventaires piscicoles. L'utilisation d'un pas de temps de calcul hebdomadaire semble plus appropriée qu'un pas de temps mensuel pour représenter l'effet de la température sur la population. Cependant, le modèle dans son état actuel ne permet pas de représenter de façon satisfaisante l'impact du fort accident climatique observé en été 91 ; il donne par contre une bonne image de la restauration de la population de géniteurs à partir de 1992. Increasing numbers of simulation tools are currently becoming available to evaluate the impact of various types of water uses on the aquatic ecosystem ; one of these is a model of the dynamics of brown trout (Salmo trutta) populations, now being developed. To complement the considerable data already available on the l'Oir valley (Lower Normandy, France), inventories as well as specific experiments were conducted in 1996 to verify and complete the different model components, especially in terms of the biological functions involved. In particular, a habitat study enables determining the carrying capacity of the environment and therefore a density-dependent component in survival of young troutlets ; reproductive potential is estimated with the aid of blood samples and the sacrifice of a few mature females. Any exchanges with the downstream reaches of the valley are quantified by means of a trapping system. The results of these experiments enable an initial application of the model to the valley as a whole and a comparison of the simulations performed with data obtained from fish inventories. Use of a weekly time step for calculations appears more appropriate than a monthly step, in representing the effect of temperature on the population. However, the model in its present state does not give a satisfactory representation of the impact of the major climatic event observed in summer 91 ; it does, on the other hand, provide a good representation of the restoration of the population of genitors beginning in 1992
A mathematical model representing the long-term change in a trout population under different rive... more A mathematical model representing the long-term change in a trout population under different river management scenarios is presented. It describes the structure of a population broken down into age classes based on the Leslie matrix; if the population structure for any given month is known, the model should be able to estimate that of the following month. The passage from one month to the next takes into account various relevant factors: survival rate of individuals in the different age classes; fertility rate of females; linear and weighted growth rates; displacement linked to habitat fluctuations using weighted usable area (WUA) values. The model was applied to two French rivers. Regular monitoring of trout populations on the River Kernec enabled comparison of the response of the model with no displacement, with actual variations in fish stocks on the first river. In addition, the knowledge of WUA chronologies on the River Echez made it possible to carry out initial simulations of the response of a fish population to different river management scenarios at the second site.
Sur quelles connaissances se baser pour évaluer l'état de santé des populations de truite commune... more Sur quelles connaissances se baser pour évaluer l'état de santé des populations de truite commune (Salmo trutta)?
Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in... more Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the physical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations (Ance du Nord and Oriège). Application of this methodology to hydropeaking conditions requires additional habitat descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; hydropeaking effects on habitat parameters are different in wide and in deep profiles. It is suggested that, in both instances, hydraulic refugia are crucial for organisms to withstand the v...
... on Guar-anteed Flow that groups experts from different research bodies, gov-ernment agencie... more ... on Guar-anteed Flow that groups experts from different research bodies, gov-ernment agencies and Electricité de France (Merle and Eon ... carrying capacity and the occupancy rates remain very low in comparison with both the reference reach and averages for French rivers. ...
... Particularly, the flow-related habitat role simulated in the model – through a phenomenon of ... more ... Particularly, the flow-related habitat role simulated in the model – through a phenomenon of compensation during the first months of life and through displacement resulting in mortality, and mortality among fry when discharge is high – was illustrated by these examples. ...
Changes in a brown trout (Salmo trutta L.) population result from interaction among various mecha... more 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.
Despite the many habitat simulations that have been undertaken around the world, not enough biolo... more 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.
It is often difficult to determine the real impact on downstream fish populations of a change in ... more It is often difficult to determine the real impact on downstream fish populations of a change in the mode of management of a hydropower installation and, in particular, the impact of an increase in the instream minimum flow. Other factors in addition to the simple limitation of habitat in low-flow periods can influence the evolution of a fish population over time. It was often observed that the 0+ individuals appear limited by strong discharge in the first months after their emergence (March to May). In an attempt to provide some answers, a dynamic model of a trout population (MODYPOP) has been applied to the river Roizonne in the French Alps upstream and downstream of a hydropower station, in order to estimate the effect of different discharge time series on trout population dynamics. The trout populations were monitored by means of annual inventories at two study sites -one with minimum flow and the other with natural flow. At each site, the available habitat was described and simulated as it changed with the discharge, according to the "microhabitat" method (EVHA, derived from PHABSIM). Habitat time series were built on the basis of discharge time series. The MODYPOP simulations, integrating habitat and discharge time series, were compared with observed numbers of fish; the results indicate that fluctuations in discharge during the post-emergence period play a major role in the dynamics of the total population. Predictions can be significantly improved if the impact of strong discharge on emerging fry is integrated in the model.
The conclusions of numerous stream restoration assessments all around the world are extremely cle... more The conclusions of numerous stream restoration assessments all around the world are extremely clear and convergent: there has been insufficient appropriate monitoring to improve general knowledge and expertise. In the specialized field of instream flow alterations, we consider that there are several opportunities comparable to full-size experiments. Hundreds of water management decisions related to instream flow releases have been made by government agencies, native peoples, and non-governmental organizations around the world. These decisions are based on different methods and assumptions and many flow regimes have been adopted by formal or informal rules and regulations. Although, there have been significant advances in analytical capabilities, there has been very little validation monitoring of actual outcomes or research related to the response of aquatic dependent species to new flow regimes. In order to be able to detect these kinds of responses and to better guide decision, a general design template is proposed. The main steps of this template are described and discussed, in terms of objectives, hypotheses, variables, time scale, data management, and information, in the spirit of adaptive management. The adoption of such a framework is not always easy, due to differing interests of actors for the results, regarding the duration of monitoring, nature of funding and differential timetables between facilities managers and technicians. Nevertheless, implementation of such a framework could help researchers and practitioners to coordinate and federate their efforts to improve the general knowledge of the links between the habitat dynamics and biological aquatic responses.
... The need today to adopt multi-use management strategies for rivers requires that ... WUA chro... more ... The need today to adopt multi-use management strategies for rivers requires that ... WUA chronologies were reconstituted using available chronologies of discharge from 1988 to 1998 for ... Monitoring of the populations present (fecundity, growth, etc.) and knowledge of the habitat ...
The Orlu hydroelectric power plant on the River Orikge is managed by 'hydropeaking' and generates... more The Orlu hydroelectric power plant on the River Orikge is managed by 'hydropeaking' and generates significant and frequent daily fluctuations in flow downstream. Observations at this site aimed to determine the impact of these variations on the aquatic environment. Surveys were carried out in June and October, upstream and about 2 km downstream of the plant, with a view to studying fish feeding habits and nutritive resources. In June, when the natural river flow was high, invertebrate populations differed very little between the two sectors. In October, after the low-water period, density and biomass were significantly lower in the downstream sector than they were upstream. Invertebrate drift was studied by taking samples every hour over a 24-hour cycle. Upstream, this drift showed a clear daily rhythm, dominated by nocturnal drift. Downstream in June, invertebrate drift was more abundant than upstream; a similar nychthemeral rhythm was apparent, but there were significant peaks during hydropeaking. In October, this daily rhythm disappeared, and drift was extremely low when river flow was low; on the other hand, a marked increase was observed during hydropeaking. Fish feeding habits were studied parallel to drift by capturing about 20 fish every four hours and analysing their stomach contents. No clear rhythm in the daily food uptake was observed. Stomach content was more abundant downstream. Lastly, the number of prey captured by fish at a given period of the day did not appear to be linked with the effective quantity of invertebrates simultaneously available in the river.
... aim of this paper is to illuminate any environmental preference of brown trout (Sulma tritttu... more ... aim of this paper is to illuminate any environmental preference of brown trout (Sulma tritttu, fario) in streams of the South of France and, in ... The presence of fish was checked by using two special electric fishing techniques: (1) casting the anode ahead of the operator for a sudden ...
Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in... more Hydropeaking generates significant fluctuations in flow in downstream river reaches, resulting in frequent and major changes in the physical conditions of the fish habitat. The microhabitat methodology, derived from the IFIM, focuses on minimum flow studies in by-pass sections, but has been adapted to two rivers subject to daily flow fluctuations (Ance du Nord and Orikge). Application of this methodology to hydropeaking conditions requires additional habitat descriptors to take into account the temporal aspects of peaking flows and their effects on trout habitat, i.e. flow and habitat chronologies analysed in duration and frequency. Hydropeaking and the natural upstream flow regime were compared. The results show that habitat variations are closely related to the flow regime and site morphology; hydropeaking effects on habitat parameters are different in wide and in deep profiles. It is suggested that, in both instances, hydraulic refugia are crucial for organisms to withstand the variations of physical variables. This approach helps in better understanding the physical limiting factors in situations of short-term flow fluctuations.
Bulletin Français de la Pêche et de la Pisciculture, 1993
ABSTRACT L'objectif est de quantifier le rôle des abris et caches des rivières aménagées ... more ABSTRACT L'objectif est de quantifier le rôle des abris et caches des rivières aménagées sur le peuplement des truites fario. L'étude s'est déroulée sur deux tronçons de cours d'eau pyrénéens : la PIQUE (altitude 920 m NGF) et le GER (altitude 390 m NGF), situés dans le département de la Haute-Garonne (31). Pour les caches naturelles, nous avons expérimenté sur trois ensembles qui ont pu être transitoirement condamnés par des grillages : enrochement des berges, caves creusées sous les berges, et branchages. Ceci a pu être réalisé sur le GER. Initialement, le secteur (avec tous ces types de caches) possède une densité moyenne de 2469 ind/ha pour une biomasse de 278 kg/ha. Quand l'accès aux caches est condamné, la densité se stabilise à 1000 ind/ha pour une biomasse d'environ 125 kg/ha, soit une diminution de l'ordre de 55 % en densité et en biomasse. Suivant les types de caches, la recolonisation, après 21 jours de réouverture des caches, est estimée entre 28 et 72 % pour la biomasse et entre 42 et 62 % pour la densité. Pour les caches artificielles, six types de matériaux de construction (brique, tuile...) ont été expérimentés sur un tronçon de la PIQUE (dénudé de toute cache naturelle). Suivant les types de caches et leur disposition, la densité des truites varie de 3 à 23 ind/m2 de cache, et de 0,09 à 0,2 ind/m2 hors cache. Parmi les matériaux utilisés, on observe une nette préférence pour les briques et, selon les dispositions testées, les meilleurs résultats sont obtenus avec les caches placées soit près, des rives, soit dans la totalité du lit. L'expérience a montré le rôle prépondérant des caches naturelles et artificielles sur le peuplement des truites dans un cours d'eau aménagé. The aim of this study was to quantify the role of various cover types and examine their selection by brown trout. The study was developed on two river course sections in the Pyrenees : the river PIQUE (altitude 920 m NGF) and the river GER (altitude 390 m NGF), situated in the department of the Haute-Garonne (31). For the natural cover, we have experimented on three sets which have been transitionnally blocked by wire netting ; rocky river bank, undercut bank and woody debris. This has been performed on the river GER. Initially, the sector, for ail these types of covers, had an average density of 2469 ind/ha for a biomass of 278 kg/ha. When the access to the covers is protected, the density stabilises to 1000 ind/ha, being a decrease in the order of 55% in density and biomass. According to the type of cover, the recolonisation, after 21 days of reopening of the covers, is estimated between 28 and 72% for the biomass and between 42 and 62% for the density. For the artificial covers, six types of building materials (brick, tile...) have been experimented on the river PIQUE section (ail natural covers having been removed). By type of covers and their location, the trout density varied from 3 to 23 ind/m2 of cover, and from 0.09 to 0.2 ind/m2 outside cover. Among the material used, we observed a clear preference for brick and, depending on the dispositions tested, the best results have been obtained with the covers placed near the banks, or being in the totality of the bed. The experiment has shown the major rôle the natural and artificial covers have on trout populations.
Bulletin Français de la Pêche et de la Pisciculture, 1998
ABSTRACT Afin d'évaluer l'impact des différents usages de l'eau sur l&... more ABSTRACT Afin d'évaluer l'impact des différents usages de l'eau sur l'écosystème aquatique, des outils de simulation de plus en plus nombreux voient actuellement le jour ; dans ce cadre, un modèle de dynamique de population de truite (Salmo trutta) est en cours de développement. Pour enrichir les nombreuses observations déjà disponibles sur le bassin de l'Oir (Basse-Normandie), des inventaires assortis d'expérimentations spécifiques ont été effectués en 1996 pour conforter et compléter les différentes composantes du modèle, en particulier en ce qui concerne les fonctions biologiques impliquées. En particulier, l'étude de l'habitat permet de déterminer la capacité d'accueil du milieu et ainsi une composante densité-dépendante de la survie des jeunes truitelles ; le potentiel reproducteur est appréhendé à l'aide de prélèvements sanguins et du sacrifice de quelques femelles matures. D'éventuels échanges avec l'aval du bassin sont quantifiés à l'aide d'un système de piégeage. Les résultats de ces expérimentations permettent d'effectuer une première application sur l'ensemble du bassin et de comparer les simulations obtenues aux données issues des inventaires piscicoles. L'utilisation d'un pas de temps de calcul hebdomadaire semble plus appropriée qu'un pas de temps mensuel pour représenter l'effet de la température sur la population. Cependant, le modèle dans son état actuel ne permet pas de représenter de façon satisfaisante l'impact du fort accident climatique observé en été 91 ; il donne par contre une bonne image de la restauration de la population de géniteurs à partir de 1992. Increasing numbers of simulation tools are currently becoming available to evaluate the impact of various types of water uses on the aquatic ecosystem ; one of these is a model of the dynamics of brown trout (Salmo trutta) populations, now being developed. To complement the considerable data already available on the l'Oir valley (Lower Normandy, France), inventories as well as specific experiments were conducted in 1996 to verify and complete the different model components, especially in terms of the biological functions involved. In particular, a habitat study enables determining the carrying capacity of the environment and therefore a density-dependent component in survival of young troutlets ; reproductive potential is estimated with the aid of blood samples and the sacrifice of a few mature females. Any exchanges with the downstream reaches of the valley are quantified by means of a trapping system. The results of these experiments enable an initial application of the model to the valley as a whole and a comparison of the simulations performed with data obtained from fish inventories. Use of a weekly time step for calculations appears more appropriate than a monthly step, in representing the effect of temperature on the population. However, the model in its present state does not give a satisfactory representation of the impact of the major climatic event observed in summer 91 ; it does, on the other hand, provide a good representation of the restoration of the population of genitors beginning in 1992
A mathematical model representing the long-term change in a trout population under different rive... more A mathematical model representing the long-term change in a trout population under different river management scenarios is presented. It describes the structure of a population broken down into age classes based on the Leslie matrix; if the population structure for any given month is known, the model should be able to estimate that of the following month. The passage from one month to the next takes into account various relevant factors: survival rate of individuals in the different age classes; fertility rate of females; linear and weighted growth rates; displacement linked to habitat fluctuations using weighted usable area (WUA) values. The model was applied to two French rivers. Regular monitoring of trout populations on the River Kernec enabled comparison of the response of the model with no displacement, with actual variations in fish stocks on the first river. In addition, the knowledge of WUA chronologies on the River Echez made it possible to carry out initial simulations of the response of a fish population to different river management scenarios at the second site.
Sur quelles connaissances se baser pour évaluer l'état de santé des populations de truite commune... more Sur quelles connaissances se baser pour évaluer l'état de santé des populations de truite commune (Salmo trutta)?
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