removed fiom the stream, placed immediately in 

 chipped ice, and brought to the laboratory for iden- 

 tifying, counting, and weighing. Fifty-two separate 

 collections were made in this initial inventory. 



After the initial inventory had been completed 

 on September 5, 1950, the 4-mile length of stream 

 under intensive study was marked off into eight 

 divisions for further investigation of the stream it- 

 self and of the fish found in each division. As the 

 divisions were set up, no pool was split; each pool 

 was entirely within a single division. Fortunately, 

 the lower seven divisions could be made equal in 

 length (0.53 mile each), as determined from topo- 

 graphic maps and aerial photographs. Since these 

 lower seven divisions were each slightly over one- 

 half mile in extent, the eighth division of the 

 4-mile length was shorter than the others, only 

 0.31 mile in length. Deeper water and shade under 

 a concrete road bridge that marked the upper limit 

 of this last division attracted a concentration of 

 fishes at that point. The fish populations cen- 

 sused in this division, even though modified by the 

 shorter length of the stream and by the bridge, 

 were compared with the populations in the 

 other divisions. 



During the months of September, October, and 

 November, 1950, many pools were reworked once to 

 several times. The same procedures were followed 

 as were used during the initial census, except that 

 the fishes returned to the stream were marked with 

 numbered opercular tags. By repeated censuses of 

 certain pools, much information was gathered con- 

 cerning fish movements and the effects of removing 

 a large percentage of the forage fish population. 

 The fish taken in these repeat censuses are not 

 included in the original tabulations, tables 2-9. 

 However, several additional species collected 

 during the fall months are included in the species 

 list, table 1, and in the discussion of species. 



Description of Drainage Bosin 



Jordan Creek, a warm- water stream 11 miles 

 long, drains a glaciated area of 10.6 square miles 

 in the southern part of Vermilion County. During 

 the Glacial Epoch, at least two ice sheets, the 

 Illinoian and the Wisconsin, covered this region. 

 The more recent Wisconsin glacier largely deter- 

 mined the topography and soils. The source of 

 Jordan Creek is in a part of Vermilion County that 

 was left as a flat, marshy area by the last 

 glaciation. The soils of this flat area are primarily 

 of two types: Drummer clay loam and Brenton silt 

 loam (Wascher, Smith, & Smith 1938). These soils 



were formed under slough-grass and prairie-grass 

 vegetation. Because of the poor natural drainage 

 of this flat land, the upper half of Jordan Creek was 

 dredged to improve the drainage and make these 

 soils suitable for farming. 



The stream flows northward out of this flat 

 land into an area of rolling to rough topography. 

 Here the stream has not been dredged. In this 

 lower part of Jordan Creek is the 4-mile study 

 section, which is divided naturally into two con- 

 trasting habitats of about equal lengths: a lower, 

 wooded area and an upper, open area. 



Lower, WoodeJ Area. --This area, which in- 

 cludes the first 2 miles above the mouth of Jordan 

 Creek, covers the lower four divisions of the study 

 section, fig. 2. Here the rough, rolling land through 

 which the stream flows has scattered ridges of 

 glacial materials and frequent outcroppings of 

 bedrock. 



In this area Jordan Creek falls an average of 

 24 feet per mile. Flowing rapidly across the ex- 

 posed edges of underlying rock strata as it neais 

 the Vermilion River, the stream forms more frequent 

 pools and steeper riffles than in the upper area. 

 Besides the siltstone, sandstone, and shale that 

 comprise the bedrock, gravel is a predominant 

 bottom material. Sand and silt bottoms are not 

 common. Midway in this lower, wooded area, the 

 volume of stream flow is approximately 18.6 cubic 

 feet per second at average water levels. 



Heavy vegetation covers most of the stream 

 banks in the lower area, fig. 3. American elms, 

 sugar maples, silver maples, cottonwoods, syca- 

 mores, and many other large trees shade the water. 

 Even away from the wooded creek margins there 

 are extensive stands of hardwood timber. Farming 

 is limited primarily to stock raising on permanent 

 pastures. Vance silt loam is the common soil type 

 in the lower half of the study section (Wascher, 

 Smith, & Smith 1938). This soil erodes easily, so 

 that plowing is limited to a few flat areas and small 

 garden plots. 



Upper, Open Area. --The upper half of the 

 study section, which is in open farm and pasture 

 land, includes the 2 miles of stream in the upper 

 four divisions, fig. 2. The topography of this area 

 is flat to rolling. Generally only 10 to 15 feet of 

 soil covers the bedrock, but there are no out- 

 croppings except in the bed of Jordan Creek. The 

 stream has cut through the overlying soil, so that 

 its gradient and bottom materials are determined 

 largely by the bedrock. 



In this area, in contrast to the wooded area, 

 the stream flows over the flat surfaces of rock 

 strata and only occasionally cuts entirely through 



