regions show intermediate poundages. This 

 generalization is strengthened by the infor- 

 mation presented in table 10, which tends to 

 show that the average total standing crops are 

 greater in more southerly regions . The major 

 differences, however, are reflected primarily 

 in the abundance of fish in the rough -fish group. 



Game-fish production in area B exceeded 

 that reported for northern Wisconsin, northern 

 and southern Minnesota, and Iowa but was simi- 

 lar to that shown for southern Wisconsin and 

 Illinois . The average standing crop of panf ish 

 in area B A-as similar to that found in northern 

 waters, but less than that found in lakes further 

 south. 



The mean proauction of the combined 

 panfish and game-fish groups was higher in 

 area B than in lakes of the north and slightly 

 greater than that reported for Iowa, central 

 Illinois and Illinois River floodplain lakes . It 

 was less than the average standing crops of 

 those species in southern Minnesota, southern 

 Wisconsin, and in three Illinois lakes. 



SIZE AND AGE-GROUP COMPOSITION OF 

 POPULATION IN AREA B, 1948-1949 



specimens were recovered, of which 62 ranged 

 from 17.0 to 24.9 inches in an uninterrupted 

 1-inch interval setpience. Forty of the latter 

 group fell within the 21 .0- to 23.9-iQch interval. 

 The 1948 sample did not indicate the presence 

 of a strong size class which aiq)eared in the 1949 

 collection as a group of larger fish . The scarcity 

 of fish under apiproxiraately 17 inches in both 

 years and in 1951 and 1952, as well, suggests 

 that yoimg and juveniles of this species do not 

 generally inhabit backwater areas of this type 

 in summer. 



Shortnose gar; --Twenty-one specimens of 

 shortnose gar under 8 .0 inches in length (pre- 

 sumably of age group 0) and 12 between 15 .0 

 and 25 .9 inches were collected in 1948 . In 1949 

 only 2 fish of the former size were recovered 

 hile 57 between 17 .0 and 25 .0 inches were 

 collected . 



Longnose gar;--T"-e :;-ree specimens 

 collected in 1948 were :.:: ir .-.e 18.0-18.9-inch 

 interval. Two size groups, 5.0-11.9 inches 

 and 19.0-28.9 inches, were present in the 1949 

 collection of 34 fish . 



Game fish 



The total standing crop of a water area is 

 an index of its biological productivity, but the 

 potential harvestable crop wUl depend on the 

 size and age structure of the population. A 

 dascription of this structure in area B at the 

 time of fish removal in 1948 and 1949 is pre- 

 sented below . Age-frequency distribution In 

 the various samples was determined by aging 

 a number of fish within certain size ranges and 

 then assigning ages to measured fish in these 

 ranges on the basis of percentage composition 

 of various size classes. Since there was only 

 a small amount of overlap between the intervals, 

 a reasonably accurate estimate of age compo- 

 sition of the enti re population was obtained . 



SIZE AND AGE STRUCTURE 



Predators 



Bowfin:--In the 1948 collection there were 

 28 bowfin. Of that number, 27 varied from 21 .0 

 to 25.9 inches in length ^Tahle 11). In 1949, 68 



L^rgemouth bass :--Youiig-of-the-year 

 of largemouth bass were aHmrtaTir in both years . 

 In 1948 only two and three specimens of age 

 groups I and n , respec'v^" -;s-ere recovered. 

 In the following year l4 - fish of those 



respective age groups and 3 of age group HI 

 were taken (Table 12). 



Northern pike: --Aging of scale samples 

 with a high degree of certainty was not possible 

 for northern pike so age groups cannot be defined. 

 The numbers of specimens recovered in 1948 

 and 1949 were 16 and 18, respectively (Table 11). 

 The smaUest fish in 1948 were in the 22.0-22.9- 

 inch size class , and the largest exceeded 36 inches 

 \n length. In 1949, 13 of the 18 fish ranged from 

 14.0 to 20.9 inches in length and the largest was 

 less than 30 inches. 



21 



