358 



Illinois Natural History Survey Bulletin 



Vol. 28. Art. 



industrial development have usurped a 

 considerable acreajze of the farmland. 



3. Draining and dredjiin^ reduced the 

 water-holding capacity of the watersheds, 

 resulting in a lower water table and in 

 extreme fluctuations in stream flow. Can- 

 alization altered stream courses and habi- 

 tats and produced more uniformity in 

 stream environments. 



4. Late in the nineteenth century, most 

 of the marshes and natural ponds were 

 eliminated ; many drainage ditches were 

 created. During the 30 \ears ending in 

 1959, the environmental trends in the 

 streams were toward a decrease in depth 

 and an increase in width ; a decrease in 

 gravel substrate, an increase in silt, and an 

 increase in sand ; a decrease in aquatic 

 vegetation and an increase in overhanging 

 vegetation. 



5. Ninety species of fishes were in- 

 cluded in the annotated list for Cham- 

 paign County ; 74 of these were taken in 

 1959 or subsequently. Seven of the 90 

 were introduced species; the remaining 

 83, some of them no longer in the county, 

 were native. 



6. Sixteen species, the introductions ex- 

 cluded, showed a decided increase in occur- 

 rence (number of collecting stations and 

 number of stream systems in which they 

 were found) within the county during 

 the 60-year period of study; 15 other 

 species showed a decided decrease in occur- 

 rence. Many species showed little change 

 in occurrence, despite the great changes 

 that took place in the stream habitats. 



7. During the early part of the present 

 century, the Salt Fork drainage contained 

 a greater number of species than any other 

 drainage in Champaign County; it was 

 followed by the Sangamon, Middle Fork, 

 Kaskaskia, and Embarrass. Subsequently, 

 the Salt Fork and Sangamon exchanged 

 rank. In 1959, the Sangamon contained 

 the greatest number of species restricted 

 to one drainage; the Embarrass had no 

 species that occurred in that stream ex- 

 clusively. 



8. Much greater changes in species 

 composition occurred in Champaign 

 County streams during the first 30 years 

 of the twentieth century than during 

 the second 30 years. During the first 30- 

 year period, the greatest changes occur- 

 red in the Middle Fork and Sangamon 



drainages; during the second 30-year 

 period, the greatest changes occurred in 

 the Kaskaskia and Salt Fork drainages. 



9. Champaign County streams were 

 classified as rivulets and small creeks, 

 large creeks, and small rivers. Both large 

 creeks and small rivers contained the fol- 

 lowing habitats: sand and fine gravel rif- 

 fles; gravel and boulder or rubble riffles; 

 shallow, firm-bottomed pools; and deep, 

 mud-bottomed pools. Each habitat was 

 found to have characteristic species of 

 fishes. 



10. Each factor in the habitat of a 

 species was expressed mathematically by 

 correlating the numbers and weights of 

 each species taken in quantitative samples 

 with the numerical value for each of 13 

 different ecological factors. 



11. Significant degrees of association, 

 some of which were unexpected, were 

 found between the numerical abundance 

 of Notropis dorsalis and Ericymba buc- 

 cata, Notropis chrysocephalus and Erimy- 

 zon oblongus, and Catostomus commer- 

 soni and Phenacobius mirabilis. Less signi- 

 ficant associations were found between 

 each of these species and several other 

 species and between a few other pairs 

 of species. A mutual dependence upon 

 certain ecological conditions, rather than 

 a direct interdependence between species, 

 appeared to account for the associations 

 found in Champaign County. 



12. The average number of species per 

 collecting station and the average number 

 of fish per 100 square yards of water were 

 somewhat greater in 1959 than in 1928. 

 The most pronounced differences in the 

 number of fish per unit area occurred in 

 the Middle Fork drainage (high in 1928, 

 low in 1959) and the Embarrass (low in 

 1928, high in 1959). The number of 

 pounds of fish per acre of water was 

 found to be 124.4 in 1959; it had been 

 estimated by Thompson & Hunt to be 

 150 in 1928. The number of pounds 

 of fish per 100 square yards of water in 

 1959 averaged 2.6, ranging from 0.9 in 

 the Kaskaskia to 5.1 in the Middle Fork 

 drainage. 



13. The following generalizations be- 

 tween fish distribution and stream size, as 

 postulated by Thompson & Hunt (1930) 

 following the 1928 investigation, were in 

 general borne out in the 1959 study: the 



