.^04 



Illinois Natural History Sur\ey Hulletin 



Vol. 28, Art. 2 



at each station, nor could we determine t!ie 

 efficiency of our electrofishinji at each sta- 

 tion and still complete the field work in 

 a 2-month period. To keep the number of 

 variable conditions as small as possible and 

 to obtain as nearly comparable samples as 

 was practical, we followed the same pro- 

 cedure at each station. In another stud\ 

 Larimore (1061), using equipment and 

 procedures similar to those used in the 

 105*^ survey, determined elcctrofishin^ suc- 

 cess in a stream just outside Cliampai^n 

 County. Since the stream was similar to 

 some of the Champaign County streams 

 and since many of the same species were 

 collected, his rate of success is pertinent 

 to evaluating our (luantitative samples. 



The qualitative completeness of our 

 quantitative samples, that is, the number 

 of species per station in the quantita- 

 tive samples compared with the number 

 of species per station in the quantita- 

 tive plus other samples (total collec- 

 tion per station), is shown in tables 13 

 and 14. Usually about 90 per cent of the 

 species listed at each station were taken 

 in the blocked-off area; the additional 10 

 per cent were obtained in nearby areas. 

 Our collections averaged 1.4 times as 

 many species per station as did those of 

 Thompson 6c Hunt. The difference is due 

 probably to our use of two collecting 

 methods and our larger samples. It prob- 

 ably does not reflect a change in the num- 

 ber of species present, nor does it imply in- 

 efficiency in the earlier survey, for cer- 

 tainly Thompson <Sc Hunt were remarka- 

 bly thorough with the method that they 

 employed. 



Further evaluations of our collecting 

 efficiency are given in the section General 

 Abundance and Occurrence. 



Preservation and Sorting of Col- 

 lections. — \'er\' large, easily identified 

 fishes were released at the site of capture 

 after their numbers, lengths, and weights 

 had been recorded. All small specimens 

 were immediately put into cans of 15 per 

 cent formalin and taken to the laboratory. 

 Each evening, individuals in the collection 

 were sorted ; then, for each species, the 

 numbers, total weights of various size 

 groups, and ranges in lengths were re- 

 corded on printed form cards. Only speci- 

 mens of unusual interest were saved for 

 the permanent collection. Specimens ob- 



tained from habitats adjacent to the 

 blocked-off areas were not included in 

 (juantitati\e computations. 



Habitat Data Recorded at Site. — A 

 series of standard measurements and an 

 evaluation of certain ecological factors 

 were made at each station. Water level 

 was recorded as high, low, or normal. At 

 each station, depth was measured along 

 transects at the middle and lower part 

 of the stud\' area and in the deepest part 

 of the area. Where great variation in 

 depth occurred, additional measurements 

 were taken halfway between the middle 

 and upper limits and the middle and lower 

 limits of the area. Maximum, minimum, 

 and average widths were recorded on a 

 sketch of the stream section. Current was 

 measured by timing a float as it passed 

 through a 50-foot course judged repre- 

 sentative of the water velocity at the sta- 

 tion. Turbidity was measured with a U. S. 

 Geological Survey turbidity needle. Types 

 of bottom materials, such as sand, silt, and 

 gravel, were determined, and an estimate 

 was made of the relative abundance of 

 each type. Notes were made of debris 

 and vegetation in the stream, as well as 

 of vegetation on the bank and overhang- 

 ing the water. 



Tabulations. — Quantitative data were 

 recorded on large tabular sheets similar to 

 those used by Thompson ik Hunt. Total 

 number and weight for each species in a 

 collecting area were translated into num- 

 ber and weight per 100 square yards of 

 area. This procedure facilitated compari- 

 son of our results with those of Thompson 

 cSc Hunt. The volume of water at each 

 station was calculated and recorded, so 

 that the relations of fish numbers and 

 weights to volume could be ascertained. 

 Also, the measurements and ecological 

 evaluations discussed above were recorded 

 on each sheet. All of this information was 

 transferred to International Business Ma- 

 chine (IBM) punch cards; the results of 

 the classification and analysis of these data 

 were recorded on IBIVI work slieets, which 

 along with the original tabulations and 

 pertinent notes for both our survey and 

 that of Thompson <Sc Hunt are on file at 

 the Natural History Survey offices. 



Supplemental Distribution Rec- 

 ords. — ^In addition to making collections 

 at most of the stations set up by Thompson 



