Living on the edge: Reservoirs facilitate enhanced interactions among generalist and rheophilic fish species in tributaries

Abstract

Most lotic ecosystems have been heavily modified in recent centuries to serve human needs, for example, by building dams to form reservoirs. However, reservoirs have major impacts on freshwater ecosystem functions and severely affect rheophilic fishes. The aim of this review is to gather evidence that aside from direct habitat size reductions due to reservoir construction, competition for food and space and predation from generalist fishes affect rheophilic community compositions in tributaries (river/stream not directly affected by water retention). River fragmentation by reservoirs enables the establishment of generalist species in altered river sections. The settlement of generalist species, which proliferate in reservoirs and replace most of the native fish species formerly present in pristine river, may cause further diversity loss in tributaries. Generalist migrations in tributaries, spanning from tens of metres to kilometres, affect fish communities that have not been directly impacted by reservoir construction. This causes “edge effects” where two distinct fish communities meet. Such interactions temporarily or permanently reduce the effective sizes of available habitats for many native specialized rheophilic fish species. We identified gaps that need to be considered to understand the mechanistic functioning of distinct fauna at habitat edges. We call for detailed temporal telemetry and trophic interaction studies to clarify the mechanisms that drive community changes upstream of reservoirs. Finally, we demonstrate how such knowledge may be used in conservation to protect the remnants of rheophilic fish populations.

The effect of temperature on the dynamics of common bream Abramis brama migrations between the reservoir and its tributary

“…In our study, however, the body temperature of all observed fish individuals across seasons was comparable, indicating that fish in the reservoir occupied environments with similar temperature conditions as those in the tributary. The findings support the view that natively riverine species perform similar behavioural schema in reservoirs, for example, occupation of temperature niche, as in the riverine environment (Fernando & Holčík, 1991; Šmejkal et al, 2023). However, our data do not permit us to determine the reason for the modest difference between the winter body temperatures of individuals from the reservoir and those from the tributary.…”

“…The drive to find suitable feeding habitats corresponds with the findings that, compared to stationary individuals, migratory individuals had lower somatic conditions (Brodersen et al, 2019; Grift et al, 2001). Moreover, reservoirs may represent a more competitive environment with lower food availability (Šmejkal et al, 2023) than the inflow area of tributaries and/or structured habitats within tributaries (Benda et al, 2004; Bouska et al, 2023; Pander & Geist, 2010).…”

“…Furthermore, the comparable body size of the selected fish, which was limited by the necessary relationship between fish body mass and radio tag weight (J. D. Winter, 1983), may explain the lack of association between fish body length and thermal preference detected in our study. The limited resource availability in the reservoir and the subsequent effort of the common bream to utilise resources in the riverine environment were the probable reasons for migrations from the reservoir to the tributary (Šmejkal et al, 2023). Migrations of the species from the tributary to the reservoir reflected an effort to overcome harmful winter conditions in the reservoir, where a higher water column and low velocity reduced predation risk and energy costs (Pfauserová et al, 2021).…”

“…Lakes and reservoirs modify the temperature gradient of rivers, and riverine fish communities are replaced with pelagic species in lakes and by nonnative generalists in reservoirs (L'Abée‐Lund & Vøllestad, 1987; Liew et al, 2016; Šmejkal et al, 2023). Generalist species are not fully adapted to lentic environments; hence, their migrations into tributaries to exploit resources, for example, reproduction opportunities, spatial requirements and/or food availability, are regularly observed (Fernando & Holčík, 1991; Šmejkal et al, 2023). For example, the common bream is frequently found in lakes and reservoirs, from which it occasionally migrates into tributaries (Brodersen et al, 2019; Hladík & Kubečka, 2003).…”

First record of highly invasive Chinese sleeperPerccottus gleniiDybowski, 1877 (Perciformes: Odontobutidae) in the Elbe River Basin, Czechia

“…Additionally, common carp from pond aquaculture is commonly stocked into fishing grounds in rivers, which emphasises the importance of fish stock control (Kalous et al ., 2018). The landscapes filled with ponds and reservoirs are more susceptible to fish invasions (Šmejkal et al ., 2023), as has also been shown by the spread of IAS topmouth gudgeon and gibel carp ( Carassius gibelio ) (Lusk et al ., 2010).…”