472 U. S. BUREAU OF FISHERIES 



In Weber Lake the average amount of dry organic matter in the standing 

 crop of plankton was 930 kilograms, which was equivalent to about 9,300 kilo- 

 grams of living material ; these amounts represented 60 kilograms of dry 

 organic matter per hectare, or about 600 kilograms of living material per 

 hectare, which were equivalent to 54 and 540 pounds per acre, respectively. 

 The average standing crop of plankton in Weber Lake was only a little more 

 than 51 per cent as large as that of Silver Lake on the basis of unit area. 



Quantitative and qualitative studies of 676 bottom samples were made dur- 

 ing the summer. The general survey of the bottom population was completed 

 for five of the lakes, namely Clear, Muskellunge, Nebish, Silver, and Weber ; 

 owing to the large size of Trout Lake, much more time will be required, to 

 make an adequate survey of its bottom-dwelling animals. One of the interest- 

 ing facts brought out in the survey was the comparative abundance of the 

 bottom population in the shallow water where the bottom consisted of well- 

 compacted sand and gravel. Such a substratum is generally regarded as un- 

 favorable for insect larvae, oligochaets, and other macroscopic bottom forms, 

 but on these sandy and gravelly areas the macroscopic population ranged from 

 100 to more than 4,000 individuals per square meter. In the deeper water 

 where the bottom consisted of mud, or a mixture of mud and sand, the number 

 of individuals varied from none up to a maximum of about 9,000 per square 

 meter. A considerable number of samples from the deepest portions of these 

 lakes did not contain any macroscopic organisms, but all of the shallow-water 

 samples contained at least a few organisms. The chief constituent of the bot- 

 tom population, both in the shallow water and in the deeper areas, consisted of 

 chironomid larvae. Snails were especially abundant in some of the shallow- 

 water areas. 



The stomachs of 3,000 fish were examined for their food content. Of this 

 number approximately 1,000 were found to be empty, leaving 2,000 specimens 

 for analysis. Among those containing food material, there were 725 perch, 

 470 rock bass, 233 bluegills, and 273 ciscoes ; the othei'S consisted of game fish, 

 minnows, and suckers. 



The following table gives the average percentage of the more important 

 items found in the stomach contents of the 725 perch. 



Average 

 Item percentage 



Caddis-fiy larvae 22. 



Fish 12.3 



Cladocera (chiefly Daphnia) 8.5 



Hexagenia larvae 7. 5 



Chironomus larvae and pupae 6. 5 



Crayfish 4.8 



Amphipods 3. 6 



Plant material 3.4 



Total in 8 items 68. 6 



The eight items included in the table constituted a little more than two- 

 thirds of the total stomach contents, while a little more than one-third con- 

 sisted of caddish-fly larvae and fish. Cladocera ranked third in importance. 

 In addition to the above figures, it may be noted that 7 small perch of the 

 1931 brood contained 56 per cent Cladocera and 41 per cent Copepoda. 



The stomachs of the 470 rock bass contained the following percentages of 



material. 



Average 

 Item percentage 



Dragon-fly larvae 11. 



Chironomus larvae and pupae 9. 8 



Fish 8. 9 



Hexagenia larvaae 7. 8 



Crayfish 7. 6 



Caddis-fly larvae 5. 2 



Plant material 5.0 



Snails 2. 5 



Total in 8 items 57. S 



