Table 9: — Standing crops cf species grc>ups fro3 ^.cr^r.em and southern 

 sections of the -opper )*ississippi Hiver rackvaters expressed 

 kS Bounds oer acre. 



1/ Average of 4 years; iig-ires are rcunded to nearest pouM. 

 2/ Indodee 20.7 pourtds per acre listed as ^fisceUaneoos". 



Comparison witli other waters 



Valid comparison of standing crops may 

 be difficult for several reasons: there may be 

 different methods of procuring population data, 

 e.g. , poisoning and mark-recovery (Carlander, 

 12); there is a lack of estimates from repre- 

 sentative waters (Solman, 50); the number of 

 samples is insufficient; and some authors do 

 not present data in a form from which com- 

 parable elements may be extracted. Swingle 

 and Smith (56) pointed out that the weight of 

 fish which can be produced in a particular 

 water varies with the species and therefore 

 that when productivity is compared, the same 

 species must be used to secure the most 

 accurate results . This approach to comparison 

 is employed here by species groups rather 

 tban w^ith individual sp)ecies . 



Mississippi River backwaters 



Information on standing crops was ob- 

 tained under the auspices of the Upper 

 Mississippi River Conservation Committee 

 from two backwater areas near Savanna, 

 Illinois (Uppsr Mississippi River Conservation 

 Committee (63) and two near Oquawka, Illinois 

 (Upper Mississippi River Conservation Com- 

 mittee, (64) (Table 9). 



These estimates suggest that standing crops 

 in the southern section are larger and have greater 

 rough fish and smaller predator and game-fish 

 components than those in the northern section of 

 the upper river. \Miile the percentage of pan- 

 fish was much lower in the southern backwaters, 

 the actual mean standing crop of this group ap- 

 proximated that of the area B average . As was 

 the case in area B in 1949 , the gizzard shad 

 strongly influenced the total productivity in the 

 two Oquawka areas. Deletion of the contribution 

 of this single species in all cases reduces the 

 difference between the two sections in average 

 standing crops of all other species combined. 

 With this omission the average standing crops 

 of the northern and southern sections were 

 approximately 225 and 294 pounds per acre, 

 respectively. The mean production of area B 

 alone without adult gizzard shad would approxi- 

 mate 285 pounds per acre, which would reduce 

 the variation to insignificance. 



Inland waters of adjacent States 



Thompson (59) noted that, in contrast to 

 the 500 pounds of fish per acre in most Illinois 

 waters , the carrying capacity of northern Wis- 

 consin and Michigan waters was about 50 pounds 

 per acre or less, and that the intermediate 

 regions with more fertile soUs than the northern 



20 



