Conservation of fish species diversity in navigable waterways

Nineteen waterways in the German lowlands were surveyed between 1992 and 1997 to evaluate their fishes conservation capacity. From 277 sites a total of 84 821 fish of 31 species was collected. Number of species in various waterways ranged from 6 to 26 with a mean±standarddeviation of 15.4±5.4. Mean species diversity was H′=1.61±0.29 (range 1.02–2.20), and corresponding evenness 0.61±0.09 (0.51–0.76). Fish communities of waterways were dominated by perch and roach, both contributing in mean 68.5±12.5% to the total catch. The mean relative abundance of threatened fish listed in “Red Data Books” of Germany or Europe was 7.83±4.82%. Percentage of artificial shoreline structures like riprap or sheet pile wall was inversely correlated to species number, species diversity and abundance of intolerant species. This study was a first approach to estimate the percentage of habitat restoration required to increase species diversity. Even the restoration of one-fifth of the river banks, the restoration of natural shoreline structures from close 0 to 20% of the bankline should result in substantial improvement of fish diversity, and significantly contribute to species conservation and persistence of viable populations of threatened fishes in waterways. In regard to such relatively low restoration effort, biodiversity conservation in waterways is compatible with long-term resource use, navigation and human needs. Even though heavily modified, waterways are also recommended for conservation issues by their large area covered as well as their substantial number of fish species.