Effects of hydraulic engineering restoration measures on invasive gobies in a large river (Danube, Austria)

David Ramler,Hubert Keckeis

doi:10.1007/s10530-019-02101-x

Abstract

Invasive gobies can have severe detrimental effects on local fish communities, however, direct methods for population control are often insufficient (i.e. fishing) or not feasible (i.e. poisoning). Indirect methods, such as habitat modifications in the course of restoration programs, appear promising but are poorly studied. In this study, we investigate the effects of different restoration measures on the abundance and occurrence of non-native gobies in the main stem of a free-flowing section of the Danube and attempt to disentangle these measures from general large-scale trends by applying a Before-After-Control-Impact design. We found three invasive goby species (racer, bighead, and round goby) in the sampling area, partly with very high abundances. Four to six years after the installation, the measures had negative (riprap removal), neutral (side arm reconnection), or positive (groyne field adaptations) effects on goby abundances. We conclude that the impact of the measures depends on the type of intervention, is species-specific, and is largely related to substrate composition. Independent from the effect of the measures, abundances of bighead and round goby dropped in the project and reference sections after the pre-survey. This general decline probably indicates a stabilization phase of the goby populations on a lower level, but may also be influenced by a major flood event. Nevertheless, our results indicate a high potential of shoreline modifications for invasive species control, calling for considering and incorporating them in river restoration programs.

Highlights

Since about 3 decades, several goby species (Teleostei: Gobiidae) of Ponto-Caspian origin are spreading over Europe and North-America (Ahnelt et al 1998; Kornis et al 2012; Ricciardi and MacIsaac 2000)
While most of the ecological functions of the natural banks were lost, these artificial, largely uninhabited structures match the habitat preferences of many goby species, further promoting their expansion
We address the following research questions: Which non-native goby species occur in the study area and how abundant are they? What are their habitat preferences? How does each goby species respond to the different restoration measures? we assume [1] that, as invasions are strongly facilitated by artificial banks made of rubble, measures that are accompanied by an exchange of this substrate type have a higher impact than measures that only change abiotic parameters, such as flow velocity or water depth; and [2] that due to differences in habitat/substrate preference, the restoration measures will have different effects on the respective goby species

Summary

Introduction

Since about 3 decades, several goby species (Teleostei: Gobiidae) of Ponto-Caspian origin are spreading over Europe and North-America (Ahnelt et al 1998; Kornis et al 2012; Ricciardi and MacIsaac 2000). All major European waterways are invaded by one or more goby species (Borcherding et al 2011; Kornis et al 2012; Roche et al 2013). Rapid dispersal is driven by a mix of long-range introductions via ballast water and active short-range migrations. It is facilitated by river modifications, such as straightened shores with riprap-reinforced banks (Gozlan et al 2010; Kornis et al 2012; Roche et al 2013). In heavily used European waterways such as the Danube or Rhine, new introductions are virtually unpreventable, and direct interventions on goby abundances are insufficient, costly and laborintensive, or come at unintentional, high ecological costs (Kornis et al 2012; N’Guyen et al 2018)

Methods

Results

Discussion

Conclusion