Fish community changes after minimum flow increase: testing quantitative predictions in the Rhône River at Pierre‐Bénite, France

Abstract

1. Many aspects of the flow regime influence the structure of stream communities, among which the minimum discharge left in rivers has received particular attention. However, instream habitat models predicting the ecological impacts of discharge management often lack biological validation and spatial generality, particularly for large rivers with many fish species. 2. The minimum flow at Pierre-Bénite, a reach of the Rhô ne river bypassed by artificial channels, was increased from 10 to 100 m 3 s )1 in August 2000 (natural mean discharge 1030 m 3 s )1 ), resulting in a fivefold increase in average velocity at minimum flow. Fish were electrofished in several habitat units on 12 surveys between 1995 and 2004. 3. Principal components analysis revealed a significant change in the relative abundance of fish species. The relative abundance of species preferring fast-flowing and/or deep microhabitats increased from two-to fourfold after minimum flow increase. A change in community structure confirmed independent quantitative predictions of an instream habitat model. This change was significantly linked to minimum flow increase, but not to any other environmental variables describing high flows or temperature at key periods of fish life cycle. The rapidity of the fish response compared with the lifespan of individual species can be explained by a differential response of specific size classes. 4. The fish community at Pierre-Bénite is in a transitional stage and only continued monitoring will indicate if the observed shift in community structure is perennial. We expect that our case study will be compared with other predictive tests of the impacts of flow restoration in large rivers, in the Rhô ne catchment and elsewhere.

Multivariate analysis of the low-flow regimes in eastern Canadian rivers

“…The LIFE scores (Lotic-invertebrate Index for Flow Evaluation; Extence et al, 1999) were clearly related to two major droughts recorded within the study period, demonstrating the impact of low-flow events on stream communities. In another recent study involving biological validation, Lamouroux et al (2006) measured a significant change in the structure of a fish community after the artificial increase of the minimum flow in a reach of the Rhône River (France).…”

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).…”

Macroinvertebrate community response to inter‐annual and regional river flow regime dynamics

“…Results from the available long-term hydroecological studies indicate that instream communities are influenced by variations in both the climatological (Bradley and Ormerod, 2001;Daufresne et al, 2003;Scarsbrook et al, 2003) and hydrological regimes (e.g., Lamouroux et al, 2006;Monk et al, 2006, Scarsbrook, 2002Wagner and Schmidt, 2004;Wood et al, 2001). However, attempts to quantify macroinvertebrate community response to river flow variability, and in particular high and low flows, are currently limited in terms of their temporal (typically <5 years study period) and/or geographical coverage (e.g., Caruso 2002;Clausen and Biggs, 1997;Sheldon and Thoms, 2006;Suren and Jowett, 2006).…”