Assessing the efficiency of connectivity measures with regard to the EU-Water Framework Directive in a Danube-tributary system

Abstract

The effect of restoring connectivity for fish by the construction of 11 fish ladders in the Pielach and Melk rivers, both tributaries to the Danube in Austria, was monitored using electric fishing and fish traps between 1999 and 2004. In order to assess the efficiency of connectivity rehabilitation measures pre-and post-project data combining electric fishing and trap catch data were analyzed by means of three fish-based assessment methods: a MUlti-Level concept for a Fish-based, river-typespecific Assessment of ecological integrity (MUL-FA), the Fish Index Austria (FIA) and the European Fish Index (EFI). The effect of adding qualitative trap catch data to electric fishing data on metrics and indices was also tested and the magnitude of the effect was related to the distance of the sites from the river mouth. The results clearly demonstrated the significant contribution of connectivity rehabilitation measures to the ecological integrity of rivers like the River Pielach where morphological conditions are good, whereas remaining channelization still limits the success of connectivity measures in the River Melk. Trap catch data were found to represent an essential source of additional information to assess the efficiency of connectivity measures shortly after their implementation. The negative correlations of the magnitude of the effect of different indices and metrics with the distance of assessment sites from river mouths obviously underline the importance of the river Danube as a source for the re-colonization process. While the indices tested were found to have limited ability to reflect short-term response of fish assemblages to continuum rehabilitation, guild metrics were able to detect improvements of the ecological status shortly after the implementation of connectivity measures. Six metrics showed significant differences between pre and post-project data reflecting the expected increase of the ecological integrity: (1) Fish Region Index (FRI; FIA, MULFA), (2) number of subdominant species and (3) number of flow-guilds (FIA), (4) number of type specific species (MULFA), (5) number of benthic species and (6) number of potamodromous species (EFI); the FRI differences were only significant when trap catch data were added. The EFI indicated a decline of ecological integrity through increases in the density of omnivorous species and the relative number of tolerant species as well as a decrease in the relative number of intolerant species. Significantly decreasing responses with the distance from the river mouth were documented by the EFI and MULFA-index, the FRI (FIA,

Topo-Bathymetric LiDAR for Monitoring River Morphodynamics and Instream Habitats—A Case Study at the Pielach River

“…The longitudinal continuum for fish migration in the Pielach River is disrupted by weirs built for hydropower use and engineering measures, but it is possible for fish to enter the first two kilometers from the Danube (Figure 1) [57]. Nevertheless, the Pielach River has retained some of its natural self-forming morphological characteristics in the studied alluvial forests of the Neubacher Au, namely periodically inundated side arms, dynamic gravel bars, large woody debris, small oxbows, inundation areas and various succession stages of floodplain forests [59]. The Neubaucher Au is part of the Natura2000 conservation area Niederösterreichische Alpenvorlandflüsse (Area code: AT1219000).…”

Migration, growth patterns, and diet of pike (Esox lucius) in a river reservoir and its inflowing river

“…Fragmentation of river habitats is recognized as a major threat to the natural function of rivers, and specifically to the life cycle of migratory fish species (Jungwirth, 1998;Zitek et al, 2008;Liermann et al, 2012). Dams causing reduced connectivity are a challenge in all types of rivers.…”

Fish as Ecological Indicators in Mediterranean Streams: The Catalan Experience

“…Restoration of fish migration should pay proper attention to dam and weir removal, which is the most environmental positive solution at medium and long term [81]; a total restoration of river longitudinal connectivity is only possible by demolishing obstacles [82]. If the obstacle cultural value or its current use (hydropower, irrigation, etc.)…”

“…Rehabilitation measures should ensure the re-establishment of at least a good ecological status of rivers according to the European Water Framework Directive (2000/60/EC). This rehabilitation should include effective fish passages, but also habitat recovery and connection with well-preserved source areas [82]. Similarly, implementation of environmental flow regimes is urgently needed because without this, other measures could be useless.…”