I 



a layer. The open area has fewer steep riffles than 

 the wooded area. The pools are long and quiet, 

 fig. 4. The stream gradient averages 9.7 feet per 

 mile and there is a flow of about 12.9 cubic feet 

 per second at average water levels. Even though 

 bedrock and coarse gravel comprise the dominant 

 bottom materials, there are extensive accumulations 

 of sand and silt in the long pools. 



Catlin silt loam is the predominant soil type 

 (Wascher, Smith, & Smith 1938) in the upper half of 

 the study section. This soil does not erode easily 

 and it is suitable for alfalfa, clover, corn, and soy- 

 beans. The land is farmed rather intensively and, 

 even though about one-thiid of it is in permanent 

 pasture, there are few trees. Most of the stream 

 in this half of the study section is exposed to 

 direct sunlight, fig. 4, being shaded in only a few 

 places by groups of cottonwoods and American 

 elms or low, overhanging shrubs. 



The sharp contrast between these two habitats, 

 figs. 3 and 4, affords an opportunity to evaluate the 

 influence of various environmental conditions on 

 the stream fauna. The situation produced by these 

 very different habitats is unusual in that features 

 ordinarily associated with lower parts of streams- 

 low gradient, long pools, and slow current--are 

 characteristic of the upper, open area, whereas the 

 more typical upstream features are found in the 

 lower, wooded area. 



Composition of the Fish Population 



Quantitative data on the fish population of 

 Jordan Creek, as given below and in tables 2-9, 

 include only those fish actually collected during 

 the initial census (July 25 through September 5, 

 1950); no estimates are given of the numbers missed 

 in collecting, and no attempt is made to evaluate 

 the population during other times of the year. 



After a period of high water in the fall of 

 1950, several species were taken that were not 

 represented in the first inventory. These species 

 are included in the list of 40 species, table 1, and 

 mentioned in the discussion of families. The 

 common names of fishes are used throughout the 

 discussions. These names, as well as the sci- 

 entific names in table 1, are those suggested by 

 the American Fisheries Society (1948), except as 

 indicated otherwise. 



Tables 2-7 are set up to show the distribution 

 of most species in the study section. The species 

 in each table are arranged in descending order of 

 weight represented in the take; those represented 

 by only a few specimens are not included. Since 



attempts have been made to classify streams on 

 the basis of the fish family that dominates them- 

 as bass streams, sucker streams, or minnow 

 streams-the distribution patterns of families are 

 also considered and then a summary is given, tables 

 8 and 9, for the five most abundant families. 



In the brief discussions of species that follow 

 in systematic order, the distribution of fishes in 

 the study section is considered in relation to four 

 primary ecological factors-stream gradient, amount 

 of water shaded, dominant bottom material, and use 

 of the surrounding land. Table 10 is a summary of 

 this relationship. 



Sucker Family 



The suckers varied more in abundance in the 

 several divisions of the stream than either the 

 minnows or sunfishes, table 8. The actual number 

 of suckers collected in each division of the stream 

 was approximately inversely proportional to the 

 stream gradient, whereas the actual weight seemed 

 to be related to the number of larger pools in each 

 division. In relation to the other families of 

 fishes, the suckers increased in abundance from the 

 mouth of the stream up through Division 4 but 

 decreased progressively farther upstream, table 9. 

 The distribution of each sucker species is dis- 

 cussed in the following paragraphs and summarized 

 in table 2. 



Quiliback.— Fish of this species showed a 

 preference for the soft mud bottoms and slow 

 currents of the upper, open part of the stream. Of 

 167 specimens taken in seven collections, all but 

 1 were from the open area and 104 of these were 

 from Division 8. The single specimen from the 

 lower half of the study section was exceptional 

 also in being the only specimen over 1 year of age. 



White Sucker. — The larger individuals of this 

 species were taken in relatively deep pools, partic- 

 ularly associated with rock ledges and moderate 

 current. They usually attempted to avoid the 

 electrical shock by swimming ahead but seemed 

 especially sensitive to the electric current when 

 forced to turn into the effective field. The fisher- 

 men around Jordan Creek catch this sucker during 

 the spring months and value it highly as a 

 food fish. 



Hog Sucker. "By weight, the hog sucker was 

 the most abundant fish in Jordan Creek. The young 

 fish of this species were found in shallow riffles, 

 whereas the adults usually were taken just below 

 riffles in gravel-bottomed pools of moderate depth. 

 The hog sucker and the white sucker frequently 

 occurred together in collections but usually were 



