Biological Survey — Erie-Niagara Watershed 



231 



estimates in pounds per acre of food as he found it in various 

 conditions and sections of the Illinois river. 



Of the 1,767 animals taken in Chara, 61.46 per cent (1,086) were 

 crustaceans, mostly the large Caledonia shrimp, Gammarus 

 linmaens, one of the best trout foods known. ''Bloodworms" or 

 midg-e larvae, another excellent trout food, formed 31.92 per cent 

 of the catch and were living in great abundance in the mud be- 

 neath the Chara. These two classes of foods constituted 93.38 per 

 cent of the total taken and are both highly desirable as food for 

 trout. Other animals taken here were beetle larvae, caddis larvae, 

 mollusks (snails), leeches but these were relatively scarce. 



In the watercress study, Caledonia shrimps formed 81.47 per 

 cent (1,675) of the 2,056 animals taken and were dominant in this 

 type of bed as they were in the Chara bed. 



By comparing the relative productiveness of these two types of 

 beds, Chara is shown to be much the better. A larger number of 

 animals (2,056) was taken in the watercress but their total weight 

 was 24.2 grams less than the total weight of the (1,767) animals 

 taken in Chara. The reason for such a wide variation in the 

 total weight of each catch seems to be due, partly, to the shrimps. 

 Those taken from Chara were exceedingly large and heavy, 10-15 

 mm. in length while those taken from the cress were mostly small, 

 3-7 mm. long and weighed considerably less. Caddis worms also 

 helped to increase the weight of the Chara bed catch as 42 were 

 taken, most of which were large in size, 8-14 mm. long while only 

 one small one was taken in the watercress. The factors con- 

 tributing to this difference in productivity of the plant beds form 

 an important and broad field for further study. 



Table 8. — Available Fish Foods of Submerged Plant Beds 



ORDER 



Crayfish and shrimps (Crustacea) .... 



Fly larvae and pupae (Diptera) 



Caddis larvae and pupae (Trichoptera) 



Aquatic bugs (Hemiptera) 



Beetles (Coleoptera) 



Mayfly nymphs (Ephemerida) 



Snails and clams (MoUusca) 



Stonefly nymphs (Plecoptera) 



Sialis larvae et. al. fXeuroptera) 



Dragonfly nymphs fOdonata) 



Miscellaneous 



Totals 



99.99 



The other types of plant beds in which crustaceans were abun- 

 dant are given as follows with the per cent formed in each by 

 this group : Curly Pondweed, 57'.96 per cent ; Fontinalis alone, 

 98.4 per cent, and Horned Pondweed, 60.61 per cent. The last 



