Long‐term brown trout populations responses to flow manipulation

Abstract

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.

Run-of-River hydropower and salmonids: potential effects and perspective on future research

“…Conversely, other studies in bypassed reaches of RoR hydropower systems documented increases in benthic diatom richness, likely due to a relaxation of predation pressure from macroinvertebrates and creation of habitat more favorable to algal growth at lower flows (Wu et al 2010b). In other cases, no conclusive evidence of effects, positive or negative, on macroinvertebrate biomass or density has been observed in bypassed reaches (Kubečka et al 1997;Sabaton et al 2008). Despite such empirical evidence of changes to water quality parameters in bypassed reaches of RoR hydropower, neither the factors influencing these changes nor the consequences for fish have been clearly identified in the studies reviewed.…”

Long‐term simulations of the dynamics of trout populations on river reaches bypassed by hydroelectric installations—analysis of the impact of different hydrological scenarios

“…However, these methods are difficult to apply to existing hydropower installations (Biggs and Jowett, 2007); some authors have shown that the entire range of discharges is not always necessary for the restoration of a viable salmonid population (Jowett and Biggs, 2006). To advance the discussion, one would need data built up over the long term, related to the hydrological regime of the installation or to experimental modification of plant management modes (Studley et al, 1995;Capra et al, 2003;Souchon et al, 2007); such experimentation has so far been unfortunately too rare (Bayley, 2002;Jowett and Biggs, 2006;Lamouroux et al, 2006;Sabaton et al, 2008). However, some methods of quantifying fish habitat as a function of discharge have indeed been developed (Milhous, 1979;Stalnaker, 1979;Bovee, 1982;Souchon et al, 1989;Sabaton et al, 1995).…”

Débits écologiques : la place des modèles d’habitat hydraulique dans une démarche intégrée

“…4) (Baran et al, 1995). Les modèles d'habitat ont par ailleurs été utilisés pour prédire, dans le temps, les effets biologiques de restauration de débits (Jowett & Biggs, 2006 ;Sabaton et al, 2008 ;Bradford et al, 2011 ;. Lorsque les modifications hydrauliques liés à la restauration des débits étaient fortes (c'est le cas de tronçons du Rhône où des débits minimaux ont été multipliés par des facteurs de 5 à 10 ; Mérigoux et al, 2015), les modèles ont permis de prédire avec précision des modifications d'abondance des espèces (poissons et invertébrés) ou de structure de communauté (ex.…”

“…5) sont convaincants (plus particulièrement pour les poissons) car ils concernent de nombreuses espèces et sont basés sur des modèles construits avant restauration, pour la plupart sur des sites indépendants des sites restaurés. De façon cohérente, lorsque les changements d'habitat sont plus modérés (c'était souvent le cas lors de l'expérience dite de la cellule « débits réservés » concernant la truite commune ; Sabaton et al, 2008), les résul-tats sont moins tranchés. & Müller, 1989) in Surber samples collected during 15 surveys (river × date) made in five rivers.…”