230 



Conservation Department 



Table 7. — Types of Submerged Plant Beds and the Weight in Grams 

 OF Available Fish Food per Square Foot Found in Each 



1 Includes shell weight of the moUusks collected. 



2 Based upon actual weight of nutritive elements from one square foot. 



It has been estimated that if Chara produces 37.0 grams of 

 animal food per one square foot, an acre of such bed would produce 

 approximately 3,553 pounds. Kichardson,* in quantitative studies 

 of the Illinois river bottom fauna, states that the highest yield 

 per acre which he found was 5,196 pounds. He also states 

 tliat these enormous yields were evidently due. at least in a 

 measure, to the sluggish current and conse(iuent heavy sedimenta- 

 tion and to the great preponderence (99 per cent) of large, thick- 

 shelled snails. Snails formed but 0.74 per cent of the total num- 

 ber of animals taken in the Chara study listed here. It is indi- 

 cated that Chara, with an estimated yield of 3,553 pounds per 

 acre, with veiy few henvy, thick-shelled snails to add to the 

 weiglit, |)r()diic<*s mii eiioi-moiis amount of available fish food. 

 Furthermore this estimate greatly exceeds most of Kichai'dson's 



* Richardson, R. E. The Small Hottotn and Shore Fauna of the Middle and Lower 

 Illinois River and its Conneetinsj; Lakes, Chillicothe to Grafton: its valuation; its 

 sources of food supply, and its relation to the fishery. State of 111. \at. Ilist. Survey. 

 Vol. XIIL Art. XV. pp. 363 .')22, Urbana, III., r921. 



