30 



U. S. BUREAU OF FISHERIES. 



feet wide) was not deeper than the 200-foot strips alongshore. The 

 zones near shore are by no means equally productive throughout, the 

 more densely populated portions manifesting definite relations to the 

 position of the channel and to other features of the stream, especially 

 those that affect the stability of the bottom. Productive areas usually 

 occur in parts of the shore strips that are bathed by the current, or 

 where the channel approaches the shore. Character of bottom soil is 

 a significant feature, but this is often controlled by current, topog- 

 raphy, and other conditions. 



Keokuk Lake, formed in the Mississippi River above the dam at 

 Keokuk, has been examined some years after its formation to de- 

 termine some of the effects of the changed conditions. A report of 

 the observations is in process of preparation. 



STUDIES OF INLAND LAKES. 



The Bureau has continued to cooperate with the Geological and 

 Natural History Survey of Wisconsin in biological and chemical in- 

 vestigations directed at the fundamental problems of the capacity of 

 inclosed waters for support of fish life. As has hitherto been stated, 

 the Bureau bears only a relatively small proportion of the expense of 

 the investigation. Substantial progress has been made, as is indicated 

 by the following outline submitted by President Edward A. Birge 

 and Chancey Juday representing the State Survey : 



1. The bulletin dealing with the quantity and chemical composition of the 

 plankton of the lakes situated in the vicinity of Madison is now ready for the 

 press. During this investigation 481 observations have been made on the net 

 plankton and 182 on the nannoplankton of these lakes, making a total of 663 

 catches. These catches were combined into 374 samples for the chemical 

 analyses. About 2,500 separate chemical and ash determinations have been 

 made on these samples and 52 samples of special material obtained during the 

 progress of this work. 



The quantity of dry organic matter in the total plankton of Lake Mendota 

 (net plankton plus nannoplankton) varied from a minimum of 230 pounds per 

 acre in February to a maximum of 521 pounds per acre in December in the area 

 situated within the 20-meter contour line. When the surface of the entire lake 

 and the volume are taken into account the range is from 126 pounds per acre 

 in February to 256 pounds in -December. The live weight of the organic matter 

 is 10 times as much as the dry weight. 



Of the dry organic matter an average of 44.5 per cent consisted of crude 

 protein, 7.5 per cent ether extract, and 5.3 per cent crude fiber, leaving 42.7 per 

 cent to be designated as nitrogen free extract (chiefly carbohydrates). The 

 pentosans were the only carbohydrates studied, and they constituted an average 

 of 4.6 per cent of the organic matter. 



Lakes Monona and Waubesa yielded larger quantities of total plankton. The 

 amount in the former varied from a minimum of 276 pounds per acre in July to 

 a maximum of 1,063 pounds of dry organic matter in October in the 'area 

 bounded by the 20-meter contour. For the entire lake the range was from 111 

 pounds to 426 pounds per acre of surface. The maximum crop of plankton in 

 Lake Waubesa yielded 862 pounds of dry organic matter per acre in the area 

 bounded by the 10-meter contour, or 415 pounds per acre for the entire lake; 

 the average for 16 samples is 216 pounds of dry organic matter per acre. 



The dry organic matter in the total plankton of Lake Monona contained 57.5 

 per cent of crude protein, 4.8 per cent of ether extract, 4.7 per cent of pen- 

 tosans, and 4.4 per cent of crude fiber. The total plankton of Lake Waubesa 

 yielded an average of 48.6 per cent of crude protein, 4.6 per cent of ether ^ex- 

 tract, 5.8 per cent of pentosans, and 4.4 per cent of crude fiber. 



2. Mr. Wilson's numerical results for the bacteria of Lake Mendota show 

 that the average number from surface to bottom in 23.5 meters of water was 

 3,000 per c. c. of water in July and August, 1919 ; in the following autumn and 



