Streamflow Regulation and Fish Community Structure

Abstract

Many regulated streams are characterized by high variable and unpredictable flow regimes. Since changes in streamflow directly modify physical habitat, streams with such highly variable flows provide highly unstable aquatic habitats. We evaluated the effect of artificial streamflow fluctuations on stream fish communities by comparing fish densities, in species and habitat groups, between two rivers differing in daily flow regime: on with with a natural flow, and one with highly regulated flows. We developed a simple model describing the relationship between available streams habitat and its use by 15 species or size classes of fish in the natural river. Species and size classes that used a specific set of microhabitat conditions were identified by comparing habitat characteristics for samples with and without each type of fish; for fish that used a particular type of microhabitat, we grouped species and size classes according to similarity in microhabitat use. Next, we categorized stream habitat samples in both the natural and regulated rivers into groups on the basis of fish habitat use criteria. Fish densities for each fish and habitat group were ten individually compared between the two rivers. An abundant (>90% of all fish) and diverse (nine species) group of small—fish species and size classes were restricted to microhabitat that was characterized as shallow in depth, slow in current velocity, and concentrated along stream margins. This group of fish was reduced in abundance in the regulated river and absent at the study site with the greatest flow fluctuation. Another fish group included species and size classes that used either a broad range of habitat or a microhabitat that was deep, fast, or both, and was concentrated in midstream areas. The density of fish in this group was higher in the regulated river and peaked at the sites with the greatest fluctuations in flow. Highly variable and unpredictable flow regimes appear to be a high—frequency disturbance that effects fish differently depending on the way they use stream habitat and acts to reduce community complexity.

Habitat use by the fish assemblages of two chalk streams

“…1): the first site (in the first transect) was adjacent to one bank, the second (in the second transect) in the centre of the channel and the third (correspondingly in the third channel) adjacent to the opposite bank and so on. At each sampling site fish were captured in an area of approximately 1 m 2 using a pre-positioned electrofishing square (Bain et al, 1985(Bain et al, , 1988Weddle & Lester, 1993). The sampler was a 0.75*0.75 m frame (the effective area of the sampler for the average size of fish captured was approximately 1 m 2 ) electrified through a 10-m extension cord, which was connected to a Honda EG 1900X generator (230-240 VAC, ) positioned on the bank (Fig.…”

Modélisation des impacts de la gestion des débits réservés du Rhône sur les peuplements piscicoles

“…La variabilité temporelle des débits est également un facteur pouvant favoriser la diversité (HORWITZ, 1978 ;BAIN et al, 1988), et la durée des périodes pendant lesquelles les conditions d'habitat sont limitantes est à prendre en compte (CAPRA et al, 1995). En particulier, il serait intéressant de mieux quantifier l'intérêt de la modulation temporelle des débits réservés qui existe sur la plupart des RCC (Tableau II), voire de tester I'impact de modulations plus fréquentes qui rendraient les hydrographes des RCC plus proches d'une situation naturelle.…”

L'habitat à l'échelle locale : distribution multiparamètre des poissons d'eau courante

“…The West River was another largely wadable stream that was sampled (864 microhabitats) in 1982and 1983(BAIN et al, 1988 producing data on 3,039 fish of 23 species. For brevity, select results are presented for two species representing extrêmes of microhabitat use, and results are summarized for two streams with diverse and well sampled fish faunas.…”

“…Thèse were comparative, unregulated and regulated river studies of fish community composition and species-level microhabitat use. Study area descriptions and results of thèse studies have been reported by BAIN et al, 1988 ;KINSOLVING and BAIN, 1993 ;SCHEIDEGGER and BAIN, 1995. Here, I use the data from the unregulated rivers (West River in the northeastern United State [Vermont] and the Cahaba River in the southeastern United States [Alabama]) that were included in the comparative studies.…”