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Keywords:

  • fish assemblage;
  • large river;
  • lowland river;
  • habitat bottleneck concept;
  • minimum flow;
  • fisheries statistics;
  • time series

Abstract

Thirty-seven years of fisheries records covering a fishing area of 6231 ha in the lower Havel River, Germany, have been analysed to address two issues: (1) detection of the effects of habitat bottlenecks caused by extreme floods and droughts on adult fish assemblage; and (2) evaluating the appropriateness of commercial fisheries statistics in testing the habitat bottleneck concept. Time series analyses of the data were first tested for autocorrelations and then classified using the CHAID (Chi-squared Automatic Interaction Detector) and C&RT (Classification and Regression Trees) algorithms. The significant environmental predictors revealed by these segmentation procedures were used in cross-correlations with various time series of fisheries yields. No single hydraulic flood parameter was significantly correlated with fisheries yield but two drought parameters were. The strongest predictor of native fish species was the minimum discharge during the spawning season (March to June). Although total fisheries yield typically increased in years with low flows, probably because of higher catch efficiencies, the yields of pike and pikeperch significantly decreased in the following two years. By comparison, significantly higher catches of pike, perch, asp, burbot, and ide were recorded in the three years following periods of sustained higher base flows. Our findings suggest that habitat bottleneck effects on fish assemblages have an important role in influencing fish community structure and do require further study. Information on habitat bottlenecks will contribute to the setting of ecological flow requirements and sustainable fisheries in large rivers systems. Copyright © 2005 John Wiley & Sons, Ltd.