Standing Stocks of Fish in Some Iowa Streams, with a Comparison of Channelized and Natural Stream Reaches in the Southern Iowa Drift Plain

Comparisons were made of fish populations inhabiting 11 channelized and natural stream reaches in the Southern Iowa Drift Plain and two drainage ditches in the Des Moines Lobe. Fish were sampled with rotenone, identified, enumerated, and weighed. Total densities of fish ranged from 483/ha at Cylinder Creek to 51,941/ha at Walnut Creek. Total standing stocks of fish ranged from 14 kg/ha at a channelized site on the Chariton River to 1,344 kg/ha at an unchannelized site on the same river. Number of fish species ranged from six sampled at Silver Creek to 16 sampled at Jack Creek. Channelized sites contained fewer fish and substantially lower standing stocks of fish than natural reaches; however the number of species sampled was often similar. The abundance of sport fish was significantly higher in the natural stream reaches, particularly channel catfish (lctalurus punctatus), flathead catfish (Pylodictis olivaris), bullhead (I. melas and natalis), and carp (Cyprinus carpio). The Index of Biotic Integrity average was higher at the natural stream reaches (x = 36) than channelized sites (x = 29. 7). The major differences in fish populations were due to habitat quality and diversity found in the natural sites as compared to the homogeneous habitat of channelized reaches. Iowa streams have insufficient protection from the inroads of man