Rheoreaction impacts dispersal of fish larvae in restored rivers

Abstract

Connectivity of nurseries and spawning habitats for young of the year life stage is essential for successful recruitment of fish populations and therefore provides a key indicator for river restoration measures. Models for dispersal offer the potential to draw conclusions regarding restoration scenarios and to fill knowledge gaps about possible implications for fish populations. A newly developed rheoreaction‐based correlated random walk model (RCRW), in combination with a three‐dimensional numerical model and a non‐steady‐state particle tracing model, was applied for nase carp larvae (Chondrostoma nasus) before and after a restoration project on the river Danube, Austria. Spatio‐temporal patterns of dispersal of virtual larvae, attached with rheoreactive behaviour, were analysed within both scenarios. In comparison to the heavily modified river reach, the restored reach enabled a greater amount of upstream movement from the release site and showed a generally higher variability of spatio‐temporal distribution patterns. In contrast, estimated total settlement of rheoreactive larvae was substantially higher for the situation prior to the restoration measure. By comparing model results with a previously field experiment it was found that model simulations including rheoreaction as a single behaviour for navigation could not explain the whole pattern of larval dispersal. Therefore it is highly recommended for future studies to develop larval dispersal models by considering other factors (i.e., behaviour, bio‐energetics and environmental factors) of existing and future individual‐based models, which could serve as a tool to analyse the effect of restoration measures for recruitment of riverine fish populations.

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

“…The vicinity of a local spawning habitat and subsequent drift processes determine the presence of larval rheophilic fish in nursery areas (Oesmann, 2003; Reichard et al., 2004) and connectivity between these functional habitats is an essential component for successful recruitment of rheophilic fish (Figure 1). Recent studies show that drifting fish larvae can perform rheoreaction, in which they actively move in the current of the main channel to increase their chances of reaching a suitable nursery area (Glas et al., 2020; Lechner et al., 2016, 2018; Pavlov, 1994; Zens et al., 2017). Upon arrival or after hatching, larvae are generally bound to small‐scale nursery habitat conditions (0–100 m) due to their limited swimming performance.…”

“…show that drifting fish larvae can perform rheoreaction, in which they actively move in the current of the main channel to increase their chances of reaching a suitable nursery area (Glas et al, 2020;Lechner et al, 2016Lechner et al, , 2018Pavlov, 1994;Zens et al, 2017). Upon arrival or after hatching, larvae are generally bound to small-scale nursery habitat conditions (0-100 m) due to their limited swimming performance.…”

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

“…3.1). Recent studies show that drifting fish larvae can perform rheoreaction, in which they actively move in the current of the main channel to increase their chances of reaching a suitable nursery area (Pavlov 1994;Lechner et al 2016;Zens et al 2017;Lechner et al 2018;Glas et al 2020). Upon arrival or after hatching, larvae are generally bound to small-scale nursery habitat conditions (0-100 m)…”

“…Furthermore, larval drift is an important process for rheophilic species such as nase to reach nursery areas from their spawning areas further upstream in the main channel. Rheophilic larvae can to some extent actively move in the current of the main channel to reach floodplain nursery habitats via rheoreaction (Lechner et al 2016;Zens et al 2017;Glas et al 2020). Without an upstream river-floodplain connection, many nase larvae would be unable to reach nursery grounds in restored floodplains.…”

“…The inflow channel allows larvae of rheophilic species that spawn (further upstream) in the main channel, such as nase, to reach floodplain nurseries. Nase larvae can select the best habitat for their survival via rheoreaction moving actively through the water column of the main channel in search of "exits" (Lechner et al 2016;Zens et al 2017;Lechner et al 2018;Glas et al 2020). When larvae arrive in the floodplain channel, they have roughly two options for nursery habitat: they can stay in the slow-flowing channel habitat, or they can allow the flow to move them to non-flowing riparian habitats further away from the main channel.…”