Assessing the efficiency of connectivity measures with regard to the EU-Water Framework Directive in a Danube-tributary system |
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Authors: | A Zitek S Schmutz M Jungwirth |
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Institution: | 1. Department of Water, Atmosphere and Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Applied Life Sciences, Max-Emanuelstra?e 17, 1180, Vienna, Austria
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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-type-specific
Assessment of ecological integrity (MULFA), 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, MULFA), total biomass
and for the number of type specific species (MULFA).
Guest editors: R. L. Welcomme & G. Marmulla
Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries |
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Keywords: | Fish migration Rehabilitation Assessment River Connectivity Water Framework Directive Ecological status Danube catchment |
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