Fish assemblages in a western Iowa stream modified by grade control structures

Publication Date



riprap, structures, streams, erosion, bridges, fish passage, habitat, pool, fish biomass, juvenile, bass, slope, upstream, channel, catfish

Journal or Book Title

North American Journal of Fisheries Management


Over 400 riprap grade control structures (GCSs) have been built in streams of westernIowa to reduce erosion and protect bridges, roads, and farmland. In conjunction with a companionstudy evaluating fish passage over GCSs in Turkey Creek, we evaluated the differences in fishassemblage and habitat characteristics in reaches immediately downstream from GCSs (GCSsites) and reaches at least 1 km from any GCS (non-GCS sites). The GCS sites werecharacterized by greater proportions of pool habitat, maximum depths, fish biomass, andabundance of juvenile largemouth bass (Micropterus salmoides) than were non-GCS sites. Indexof biotic integrity (IBI) scores were poor or fair (,43 on a 0–100 scale) and not significantlydifferent between the GCS and non-GCS sites. Additionally, we investigated both the longitudinalchanges in fish assemblages in this GCS-fragmented stream and the changes in fishassemblages after slope modifications of three GCSs to facilitate fish passage. Thirteen fishspecies were present throughout the study area, whereas another 15 species exhibited truncateddistributions not extending to the most upstream sampling location. After modification of theGCSs, IBI scores increased at seven of nine sites (mean increase ¼4.6 points). Also, channelcatfish (Ictalurus punctatus) were detected 7.3 km upstream at sites where, 2 years before GCSmodification, they had been absent from collections. Given the number and distribution of GCSsin western Iowa streams, understanding the effects of these structures is vital to the conservationand management of fish assemblages in this and other regions where GCSs or similar structuresare used.





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