Of the species represented in area B, 

 only the largemouth bass, bluegill, black 

 crappie, and white crappie were present in 

 sufficient numbers and sizes to warrant com- 

 parison of population structure with those In 

 other sections of the river. In the following 

 comparisons, emphasis is placed on longevity 

 of life since the limited collections and the 

 variable methods by which other populations 

 were sampled make other comparisons of 

 doubtful value. 



Largemouth bass 



The oldest largemouth bass in the com- 

 bined collections of area B was of age group III. 

 The oldest fish taken in the Illinois-Missouri 

 section of the river was of age group V (Upper 

 Mississippi River Conservation Committee, 62). 



Bluegill 



The combined 1948 and 1949 collections 

 from area B included only one bluegill of age 

 group IV and only four of age group III. Kelley 

 (25) found the oldest fish collected from the 

 Mississippi River in the vicinity of La Crosse, 

 Wisconsin in the latter half of May to be of age 

 group V . A gradual decline in representation 

 of older fish was apparent as netting progressed 

 and by September age groups IV and V had 

 disappeared from the catch. He ruled out 

 migration as a factor and ascribed the decline 

 primarily to natural mortality. Meehean (32) 

 found no bluegills beyond age group III in 

 Mississippi River sloughs of the Trempealeau 

 area. The oldest fish netted in the Illinois- 

 Missouri waters of the Mississippi River were 

 5 years of age (Upper Mississippi River Con- 

 servation Committee, 62). 



Black crappie 



The oldest black crappies in the 1948 and 

 1949 collections from area B were of age 

 groups IV and V , respectively. Kelley (25 ) 

 noted a decline in trap-net catches of 4- and 5- 

 year-old fish from May to September and con- 

 cluded the principal cause to be natural mortality. 

 The oldest specimen collected in the Illinois - 

 Missouri waters of the river was of age group 

 VI (Upper Mississippi River Conservation 

 Committee, 62). 



White crappie 



In area B in 1948 the oldest white crappie 

 was of age group IV (one specimen), and in 1949, 

 one fish of age group V was collected . Kelley 

 (25) noted that by September, very few 4- and 

 5 -year-old fish were being caught in the La Crosse 

 area and again attributed the loss primarily to 

 natural mortality. The oldest fish taken in the 

 Illinois-Missouri section of the river was of age 

 group VI (Upper Mississippi River Conservation 

 Committee, 62). 



General consideration of age structure 



Data presented in this section suggest that 

 these species in the upper Mississippi River back- 

 waters are generally short-lived. Results of an 

 investigation in several similar areas near La 

 Crosse in 1948 tend to substantiate this hypothesis 

 (Kelley, 25). Few fish of the species studied at 

 La Crosse and in the present investigation were 

 found to be greater than 5 years of age. This age 

 structure is in contrast to much of the published 

 data which show a tendency in many waters of the 

 north central States for populations of the species 

 considered to be longer-lived. 



GROWTH RATES OF FISH 



Butler and Smith (8) and Appelget and Smith 

 (1) reported on growth of the freshwater drum 

 and the channel catfish in the upper Mississippi 

 River, respectively. Eddy and Carlander (15) 

 presented limited growth-rate data on the white 

 bass and spotted sucker from the Mississippi 

 River and a general summary of the growth rates 

 of several species from the Illinois -Missouri 

 waters of the river was reported by the Upper 

 Mississippi River Conservation Committee (62). 

 Because the number of scale samples taken from 

 each species was relatively small , no attempts 

 have been made to validate the scale method for 

 the present collections . Adequate validation of 

 the method for some of the species included 

 here has not yet been presented but successful 

 employment of the scale method of aging and 

 gro\\th analysis by various investigators is 

 considered to be an adequate basis for its 

 acceptance in the present case. Eddy and Car- 

 lander (15) presented general growth summaries 

 for all species herein studied except the orange- 

 spotted sunfish, Lepomis humilis (Girard), Smith 



34 



