Environmental requirements and heterogeneity of rheophilic fish nursery habitats in European lowland rivers: Current insights and future challenges

Abstract

The large‐scale degradation of riparian ecotones and of the connectivity between rivers and their floodplains has resulted in a drastic decline of rheophilic fish populations in European temperate lowland rivers. Recent river restoration projects have had variable success in effectively restoring these fish populations. Knowledge on nursery habitat requirements is considered essential for effective population restoration. However, a detailed understanding of the role of habitat heterogeneity in young‐of‐the‐year (YOY) fish population development is limited. Therefore, we carried out a synthesis of the available knowledge on nursery habitat requirements of rheophilic fish species found in European temperate lowland rivers (<200 m elevation). From a total of 603 papers, 77 studies with primary information were selected, containing 390 associations between habitat features and YOY fish. As expected, most studies focused on static components of physical riparian habitat. Generally, YOY fish require habitats of shallow depth (<0.5 m), with slow‐flowing water (<0.2 m/s), gentle bank slope (<20°), variety in substratum types (fine sand to gravel), relatively warm water and high food availability. Surprisingly, no clear ontogenetic habitat shifts between larvae and juveniles were found, which may be explained by the limited spatial–temporal resolution of most studies. Since 2011, studies on habitat heterogeneity have increased, but few have explicitly assessed its role in relation to movement patterns of YOY fish for nursery success. Therefore, we recommend that future research focuses on fish movement patterns between habitat patches in heterogeneous (river‐floodplain) environments, to increase the knowledge base for effective recovery of rheophilic fish populations.

Effects of a Hydropower-Related Temporary Stream Dewatering on Fish Community Composition and Development: From Ecology to Policy

“…The dewatering of the HB caused both direct mortality of fish by stranding and the inaccessibility of important shallow bank habitats during the low water phase. Such areas can be crucial to fulfil critical life stages in the life cycle of many riverine fish, and with a decrease in the availability of these habitats, population effects are a logical consequence (Pander et al, 2017;Hayes et al, 2019b;Moreira et al, 2019;Stoffers et al, 2022).…”

“…In contrast to fish stranding, community effects caused by dewatering were rather strong, most likely due to the restricted habitat availability in 2021 when the dewatering phase lasted several weeks from the middle of May to the beginning of August. This time of the year falls within the main larval drift phase of riverine fish at the River Inn (Nagel et al, 2021), and these types of bank habitats usually serve as a crucial refuge area for the development and growth of fish larvae and young-of-the-year fish (Pander et al, 2017;Stoffers et al, 2022).…”

Surviving and growing in dynamic floodplains : Habitat heterogeneity drives communities of young fish in the lower river Rhine

“…materials 4.7). Size limits were derived from length-frequency distributions, consultation with fish ecology experts from the Netherlands, and a literature study by Stoffers et al (2022b)). Hybrids and other fishes that could not be identified to species level (0.007% of total catch) were removed prior to the analysis.…”

“…Many river restoration projects have however failed to achieve the expected recovery of fish communities, causing global concern about their efficacy (Palmer et al 2010;Bernhardt & Palmer 2011;Wohl et al 2015). For river restoration to be effective for fishes, it is essential to understand fishes' environmental requirements in terms of spatial scale and organisation of essential (micro)habitats for shelter, food, and spawning (Schlosser 1995;Van Looy et al 2019;Stoffers et al 2022b). The fact that the spatial scale of habitat use varies with species and mostly increases with fish size further complicates effective management of (future) river restoration projects (Wohl et al 2015;Wolter et al 2016;Polvi et al 2020).…”

“…We introduce a novel approach, explicitly linking the effect of fish habitat to biodiversity and abundances of young-of-the-year (YOY) riverine fish communities at three relevant spatial scales. Our approach uncovers generic processes essential for the successful recruitment of riverine fishes, which are applicable for the effective restoration of modified lowland rivers around the world (Arlinghaus et al 2016;Stoffers et al 2022b). With a potential sixth mass extinction looming (Barnosky et al 2011;Cowie et al 2022), studies contributing to the preservation of riverine fish biodiversity and evaluating the ecological efficacy of river floodplain restoration are of eminent importance.…”