340 



Illinois Natural History Survey Hlli.i-tin 



V^ol. 28, Art. 2 



any site ; in other words, we added 

 approximately 10 per cent more species 

 by "cruising" with a seine in adjacent 

 habitats. With the small amount of effort 

 expended, "cruisini:" furnished desirable 

 additions to the collections. 



An crage Number of Fish 

 Per 100 Square ^ ards 



Althouj^h the a\erajie numbers of Hsh 

 per 100 square yards collected in both 

 surveys varied greatly from stream to 

 stream, table 13, the county a\era^es for 

 the two surveys did not differ y;reatly ; 

 the ratio of the 1928 to the 1959 average 

 was 1 :1.2. The most striking difference 

 between the two surveys was that the 

 Middle Fork produced the greatest num- 

 ber of fish per 100 square yards in 1928 

 and next to the lowest number in 1959, 

 whereas the Embarrass \ iclded the lowest 

 number in 1928 and the highest number in 

 1959. There was no apparent habitat 

 change that might account for this dif- 

 ference. A difference of the same kind 

 was not evident in the number of species 

 taken or in the weight of tish collected in 

 the two surveys of these streams. The 

 highest ratio of increase from 1928 to 

 1959 in the number of species as well as 

 in the number of fish collected per 100 

 square yards occurred in the Embarrass, 

 although in the 1959 surve\' the number 

 of species and the pounds collected in the 

 stream were low, table 13. 



Average Weight of Fish 

 Per 100 Square Yards 



The weights of Champaign County 

 fish taken in 1959 could not be compared 

 with those taken in 1928 because there 

 were no exact weight data from the 

 Thompson & Hunt survey. Thompson & 

 Hunt ( 1930:39) estimated that they took 

 150 pounds of fish per acre in the 1928 

 collections. In the 1959 survey, the num- 

 ber of pounds per 100 square yards varied 

 from 0.9 in the Kaskaskia to 5.1 in the 

 Middle Fork and averaged 2.6 for the 

 entire county. This county average is 

 equivalent to 124.4 pounds per acre. 



The poundage figures from the 1959 

 survey should not be regarded as repre- 

 senting the total population present in 

 any of the areas fished. Using the electro- 

 fishing equipment employed in the 1959 



survey of Champaign County to fish Jor- 

 dan Creek, a small stream in adjoining 

 \'ermilion County. Larimore (1961:3-5) 

 took an a\erage of 54 per cent of the 

 weight and 51 per cent of the number of 

 the fish population present in the areas 

 fished. The Jordan Creek population 

 taken by electrofishing and other means 

 amounted to nearly 25,000 fish weighing 

 163.9 pounds per acre. If the same rate 

 of electrofishing success applied to our 

 Champaign County collections, the total 

 populations would have been close to an 

 average of 250 pounds per acre for the 

 stations worked in 1959. 



DISTRIBUTION AND 

 STREAM SIZE 



Thompson & Hunt, using their 1928 

 Champaign County collections, explored 

 both the composition and the size of fish 

 populations in relation to stream size, ex- 

 pressed as square miles of drainage basin 

 at point of collection. The\ related stream 

 sizes to the numbers and weights of fish, 

 to the average sizes of fish taken, to the 

 number of species, and to the distribution 

 of various species. They grouped their 

 collections into 10 classes according to 

 stream size at the collecting stations, be- 

 ginning with stations having 0.5-1.0 

 square mile of drainage and doubling the 

 stream sizes up to the class of 256.0- 

 512.0 square miles. 



Relationships With Stream Size 



We have analyzed quantitati\e data 

 from the 1959 survey in a manner similar 

 to that used by Thompson tSc Hunt in or- 

 der to determine whether the 1959 collec- 

 tions support the conclusions of Thompson 

 ^ Hunt (1930:41-6), given in italics 

 following paragraph headings below. In- 

 cluding only those stations receiving no 

 noticeable pollution and those visited in 

 both 1928 and 1959, table 14, we plotted 

 our data for 1959 in fig. 13 to corre- 

 spond roughl\- to the treatment shown by 

 Thompson <Sc Hunt in their fig. 6; that 

 is, we combined the data for our two 

 smallest classes of stream size and for 

 our three largest classes of stream size. 

 Thompson & Hunt combined the data for 

 their three smallest and their three largest 

 classes of stream sizes. We made no quan- 

 titative collections from the two smallest 



