Integration of Constructed Floodplain Ponds into Nature-Like Fish Passes Supports Fish Diversity in a Heavily Modified Water Body

Abstract

Fish passes facilitate fish movement in fragmented river systems, yet they can also provide important habitat functions. This study investigated the fish community composition of different constructed habitat types (fluvial habitats, floodplain ponds) within fish passes in relation to habitat characteristics in order to deduce recommendations for fish-friendly designs of such structures. Fish community structures within passes differed significantly from those in the main river, comprising a high number of rheophilic species in fluvial habitats (Thymallus thymallus, Hucho hucho, Salmo trutta, Cottus gobio, Chondrostoma nasus, and Barbus barbus), and of stagnophilic species in floodplain ponds (Rhodeus amarus, Scardinius erythrophthalmus, Misgurnus bipartitus, and Tinca tinca). During summer, floodplain ponds also provided important juvenile habitats for the target species C. nasus and B. barbus. Differences between the two habitat types in fish abundance were mostly explained by differences in macrophyte coverage, gravel, boulders, temperature, and current speed. The findings of this study stress the important habitat functions of fish passes. They also suggest that integration of diverse habitat structures, especially of currently hardly considered constructed floodplain ponds into fish passes, can greatly enhance their fish communities and contribute to the restoration of several declining target species of conservation.

Water level induced changes of habitat quality determine fish community composition in restored and modified riverbanks of a large alpine river

“…In RR, the changes in habitat quality and space were different as 2 years after restoration, only scarce bank vegetation was present compared to the other habitats. Due to the higher water level in summer, the constructed small side‐channels in RR were completely flooded, providing additional aquatic habitats resembling small branches of the former braided river (Pander et al, 2021) as indicated for variation 1 of this habitat type. Braided, anabranching river courses are nowadays scarce in Europe.…”

“…This study was conducted at the River Inn, a formerly braided river (http://www.geoportal.bayern.de/bayernatlas, Pander et al, 2021). Nowadays, this river comprises a straightened single channel intensively used for hydropower generation (run‐of‐river power plants) with embankments for flood protection.…”

The overlooked contribution of a fish bypass channel to the density and diversity of macroinvertebrate drift in a heavily modified river system

“…The high density and diversity of aquatic insect larvae can make an important contribution to the food web of nature‐like bypass systems, as previous studies have shown that these restoration measures in the River Inn are also used by highly endangered fish species such as the European grayling, which has suffered from severe declines throughout the area (Mueller, Pander, & Geist, 2018). Observations revealed that this species uses nature‐like bypass systems as spawning habitat in spring (Nagel et al, 2021), but also as foraging habitat throughout the year, as it was documented in the bypass in comparatively high densities year‐round (Pander, Nagel, & Geist, 2021). The European grayling is a typical drift feeding species, preying on macroinvertebrates drifting in the water column (Hellawell, 1971).…”

“…The fish community of this river was formerly dominated by drift feeding salmonids such as grayling and brown trout as well as several rheophilic cyprinid species. To date these species still exist, but the community has shifted toward less specialized and ubiquitous species (Pander, Nagel, & Geist, 2021; Pander, Nagel, Ingermann, & Geist, 2021). Anthropogenic alteration, particularly bank stabilization and hydropower installation, changed the former river course dramatically to a widely dammed and uniform waterbody (Pander, Nagel, & Geist, 2021).…”

“…These systems can range from rather technical solutions such as fish lifts or pool passes made of concrete to nature‐like construction schemes (Larinier & Marmulla, 2004). While rather technical solutions primarily target the migratory function, nature‐like fish bypass channels mimic habitats of formerly free‐flowing river stretches by including habitats of high and low current as well as variable bed material (Meulenbroek, Drexler, Nagel, Geistler, & Waidbacher, 2018; Pander, Mueller, & Geist, 2013; Pander, Nagel, & Geist, 2021). In recent years, an increasing number of studies have demonstrated that these types of fish passes provide important habitats for spawning and foraging, especially for threatened fish species (Meulenbroek et al, 2018; Nagel et al, 2021; Pander et al, 2013; Tamario, Degerman, Donadi, Spjut, & Sandin, 2018) and in situations where they increase temperature and flow diversity (Pander, Nagel, & Geist, 2021).…”