Response of a floodplain fish community to river-floodplain connectivity: natural versus managed reconnection

Abstract

To restore lateral connectivity in highly regulated river-floodplain systems, it has become necessary to implement localized, "managed" connection flows, made possible using floodplain irrigation infrastructure. These managed flows contrast with "natural", large-scale, overbank flood pulses. We compared the effects of a managed and a natural connection event on (i) the composition of the large-bodied fish community and (ii) the structure of an endangered catfish population of a large floodplain lake. The change in community composition following the managed connection was not greater than that exhibited between seasons or years during disconnection. By contrast, the change in fish community structure following the natural connection was much larger than that attributed to background, within-and between-year variability during disconnection. Catfish population structure only changed significantly following the natural flood. While the natural flood increased various population rates of native fishes, it also increased those of non-native carp, a pest species. To have a positive influence on native biodiversity, environmental flows may need to be delivered to floodplains in a way that simulates the properties of natural flood pulses. A challenge, however, will be managing river-floodplain connectivity to benefit native more than non-native species.Résumé : Pour rétablir la connectivité de réseaux fluviaux fortement régularisés de plaine inondable, il est devenu nécessaire de mettre en place des débits de connexion « gérés » localisés rendus possibles par les infrastructures d'irrigation dans la plaine inondable. Ces écoulements se distinguent des débordements transitoires « naturels » à grande échelle associés aux crues. Nous avons comparé les effets d'évènements de connexion géré, d'une part, et naturel, d'autre part, sur (i) la composition de la communauté de gros poissons et (ii) la structure d'une population menacée de barbues dans un grand lac de plaine inondable. La modification de la composition de la communauté après l'évènement de connexion géré n'était pas plus importante que la variabilité observée d'une saison à l'autre ou d'une année à l'autre en situation de déconnexion. En revanche, la modification de la structure de la communauté de poissons après l'évènement de connexion naturel était beaucoup plus importante que celle attribuable à la variabilité intersaisonnière et interannuelle de fond en situation de déconnexion. La structure de la population de barbues n'a changé de manière significative qu'après la crue naturelle. Si cette crue naturelle a entraîné une augmentation des taux de population de divers poissons indigènes, elle s'est également traduite par une augmentation du taux de population des carpes, une espèce parasite non indigène. Il se pourrait que, pour avoir une incidence positive sur la biodiversité indigène, les débits environnementaux dans les plaines inondables doivent simuler les propriétés des crues naturelles. L'un des défis que cela présente consiste à gérer la connectivité hydr...

Effects of historic flooding on fishes and aquatic habitats in a Missouri River delta

“…The flood pulse concept postulates that fish abundance will increase after floods as riverÀfloodplain connectivity augments habitat and resource availability (Junk et al 1989). Our results supported this prediction and previous flood research (Jurajda et al 2006;Zampatti & Leigh 2013;Stoffels et al 2014) as relative abundance of most species increased after the flood. However, the flood had distinct effects on different segments of the fish community.…”

“…The flood increased relative abundance of both introduced and native fishes, supporting previous studies in floodplain rivers (Stoffels et al 2014;Vilizzi et al 2014). Common carp, the only introduced fish that was sufficiently abundant for population assessment in this study, can have profound negative effects on aquatic ecosystems by resuspending sediments and increasing turbidity (Kloskowski 2011).…”

“…With high adaptability and prolific spawning capacity, common carp readily exploit floodplain habitats under diverse hydrological conditions (Koel & Sparks 2002;Penne & Pierce 2008;Sommer et al 2014). It is pertinent for fisheries managers to design water management strategies that benefit native species in deltas without simultaneously promoting introduced fishes (Stoffels et al 2014). Floodplain inundation alone may not be sufficient to limit introduced species (Sommer et al 2014).…”

“…Floods may also exert differential effects on introduced and native fishes. Although native fishes may be more adapted to flow regimes in their indigenous range (Minckley & Meffe 1987;Gido et al 1997), both native and introduced species may benefit from riverÀfloodplain connectivity and become more abundant after floods (Stoffels et al 2014;Vilizzi et al 2014). In some rivers, floods increase reproduction, recruitment, and population growth of introduced fishes to a greater extent than native species (Scheerer 2002;Barko et al 2006;Sommer et al 2014).…”

“…We expected that small-bodied species (i.e., typical adult length < 100 mm TL) would become less abundant and large-bodied fishes (i.e., not smallbodied) more abundant after the flood (Bice et al 2014). Moreover, we hypothesized that relative abundance of both introduced and native species and sport and non-recreational fishes would increase after the flood (Stoffels et al 2014;Vilizzi et al 2014). Our third objective was to examine the effects of the flood on aquatic habitats.…”