468 
ratios estimated by Otterstrom* and Kronheim7 for trout fed on raw fish 
or ‘‘mostly animal food”. The rate of consumption of bottom (or shore) 
invertebrates per month for the nine-months “year” works out at about 
83 pounds: 
150 & 5 
———— _ = 83.3 
9 
Expressing the bottom- and shore-fauna valuations of 1915 in mul- 
tiples of the average monthly consumption rate, we find that in July— 
October of that year there were 120 miles of the Illinois River below 
Havana whose average supplies of free-living bottom-invertebrates were 
sufficient to last at such a rate only 30 days or less beyond the date of 
collection; and 77.5 miles below Lagrange dam in which there were 
sufficient stocks to last only 3 days. The much richer stocks in the river 
above Havana, in spite of the exceedingly low valuations in the lower 
river, were sufficient to bring up the average supply for the entire 180.5 
miles between Chillicothe and Grafton to a figure of 3.1 months—which 
was also the average for the 60.5 miles between Chillicothe and Cop- 
peras Creek dam. In the reach of 59.3 miles between Copperas Creek 
and Lagrange, where an average supply sufficient for 8.5 months was 
found, there was a short stretch of 16.8 miles (immediately above Ha- ~ 
vana) where the stocks were sufficient to last for over 30 months, but a 
relatively much greater part of the bottom fauna in this locally very rich 
section was made up of large heavy-shelled Mollusca than was the case 
in any other part of the river. 
In contrast with all of these river figures except those for the 16.8- 
mile reach between Copperas Creek and Havana, the average stock of 
twelve lakes between Copperas Creek and Lagrange in July—October, 
1914—1915, included a three months’ supply of bottom fauna only for 
the whole acreage, a minimum of 25.5 months’ supply of shore animals 
living above the bottom in the weedy acreage within the 4-foot line, and 
a combined average supply of bottom- and shore-animals sufficient for 
17.4 months. (See table, p. 469.) 
Supplies of bottom animals that were well above the average of all 
the lakes studied, were shown by the Class I and Class II lakes (of the 
type of Thompson and Quiver respectively): average of five deeper 
bottom-land lakes, 4.2 months; average of two deep, sand-beach lakes, 
10.2 months. Thompson Lake in 1914 had in August to October a 6.5 
months’ supply of bottom invertebrates over its entire acreage, and a 
25.7 months’ supply of weed animals in the 1—4-foot zones—or a com- 
bined average supply, on a rough acreage basis, sufficient for 20.8 
months. The low rating of bottom-fauna stocks in the very shallow 
weedy lakes, such as Flag, Duck, Dennis, (0.6 to 1.1 months’ supply), 
* Fiskerei beretning, 1911, pp. 244—254. 
7 Bibl. der Gesamten Landwirtschaft, Bd. 34, 1907. 
ti ‘Weed fauna” catches cover the upper 9 inches only. 
