Information of a similar nature was pro- 

 vided by Robert Sharp 11/ concerning movement 

 of fish into a previously dry rearing pond near 

 the Mississippi River at the National Fish 

 Hatchery, Guttenberg, Iowa. Fish had access 

 to the pond after a rise in water level for 

 approximately 2 weeks, during which period 

 1 ,240.2 pounds (124 pounds per acre) of fish 

 had entered the area, as shown by subsequent 

 eradication (Table 35). The species comprising 

 the greatest weight were carp, bowfin, buffalo, 

 black crappie, and shortnose gar, in that order. 

 Largemouth bass and black bullheads were also 

 prominent. 



Falling water levels during the winter 

 were accompanied by a definite movement out 

 of backwater areas in pools 8 and 9 by carp, 

 northern pike, crappies, spotted sucker, and 

 bowfin (Upper Mississippi River Conservation 

 Committee, 63). Movement of these fish was 

 intensified by a sharp drop In the water stage . 

 Conversely, nets set under the ice to block 

 completely the outlet of a backwater lake near 

 La Crosse, Wisconsin, demonstrated only ran- 

 dom movement during a 43-day period when 

 only minor water-level fluctuations occurred 

 (Upper Mississippi River Conservation 

 Committee, 64). 



The catch of gill nets set in and just out- 

 side area B approximately 1 week after the 1948 

 investigation provides further evidence of fish 

 movement into backwater areas from another 

 source (Table 35). This movement cannot be 

 correlated with changes in water level, but it 

 does suggest that backwaters which become 

 de-populated through drawdown or winter-kill 

 are apt to be invaded as soon as suitable con- 

 ditions are re-established. 



Comparison of water levels (Table 37) 

 with population estimates in area B in 1948, 

 1949, 1951, and 1952 fails to show any relation 

 between water-level fluctuation and standing 

 crop. The greatest short-term changes in level 

 were between 6 BA July 31 and 7 AM August 1 , 

 1949 and between 7 AM and 6 I^ August 1 , 1949 



when a rise of 1 .03 feet and a drop of 0.8 feet, 

 respectively, occurred. The highest standing 

 crop was found in the August 3, 1949 operation. 

 In view of previously cited data the sharp rise 

 in water level mig^t account for a large influx 

 of fish, but conversely the more rapid drop 

 (though not as extensive) immediately following 

 would exp)ectedly have initiated egress . Of 

 the 4 years, levels In 1948 prior to poisoning 

 were the most stable, yet production of rough 

 fish, the group purportedly most influenced 

 by water-level change, was second only to 

 that of 1949, while the standing crop of panfish, 

 the group probably least affected, was the lowest 

 of the four estimates . 



SUMMARY AND CONCLUSIONS 



The oljectives of this study were to de- 

 termine the productivity of and the fluctuations 

 in the populations from year to year, the popu- 

 lation structure, and the rate of growth of the 

 common fish species present in backwater areas 

 of the upper Mississippi River. Some of these 

 questions have been more adequately answered 

 than others . 



1 . Estimates of total fish populations of 

 three upper Mississippi River backwater areas, 

 area A and area B near Fountain City, and 

 Miller Lake near La Crosse, Wisconsin, were 

 obtained between 1947 and 1952 by application 

 of a fish toxicant . Standing crops in one of 

 these areas were determined in 4 different years. 



2. Standing crops of fish in the six indi- 

 vidual estimates ranged from 39.1 to 604.9 

 jxjunds per acre and averaged 248.4 founds 

 per acre. Deletion of the weight contributed 

 by adult gizzard shad present in only one of the 

 collections reduced the average weight per acre 

 to approximately 225 pounds . This figure is 

 considered to be more indicative of the average 

 population . 



3. Standing crops in the backwater treated 

 on four occasions (area B) ranged from 202.4 



to 604 .9 pounds per acre and averaged 324 .2 



11/ Personal communication. 



46 



