Tlic Prnduclk'it\ of Fish Food in Oneida Lake 109 



mals are few in number, the Trichoptera being the most 

 numerous. Oligochaeta, Amphipoda, Isopoda, and dipterous 

 larvre, so abundant in shallow water, are here wanting or but 

 few in number (Table No. 22, B). 



A c()mj)arison of the three areas just described shows that 

 there is a marked decrease in the number of individuals and 

 an increase in the numerical ratio of mollusks to the associated 

 animals. The decrease in number of individuals is graphically 

 shown in the fcjllowing table indicating the number of animals 

 per unit area (16 scjuare inches) : 



Tahle No. 23 



Associated 

 Depth of water animals Mollusks Total 



I- 6 feet 17.22 19.44 36.66 



6-12 feet 1.96 2.07 4.04 



12-18 feet 48 1.88 2.37 



The mollusks are seen to decrease markedly in number in 

 the area between 6 and 12 feet in depth, being but 11 per cent 

 of the inhabitants of the same area in shallow water. In the 

 deeper water (12-18 feet) the percentage is but 6.5. The 

 number of species does not show such a striking decrease as 

 do the individuals, shallow water (1-6 feet) having 22 species, 

 deeper water (6-12 feet), 38 species, and deepest water (12-18 

 feet), 21 species. The median depth thus has the greatest 

 number of species. 



Deeper water beyond the area of Lower South Bay shows a 

 farther decrease in animal life, six dredgings (equivalent to 

 288 small unit areas) totaling 423 mollusks and 79 associated 

 animals or an average of 1.46 mollusks and .27 associated ani- 

 mals (Table No. 22, C). Amnicola and J^ahata are the 

 dominant species, the former (five species) totaling 40.8 per 

 cent and the latter (two species), 18.4 per cent. One species 

 of Amnicola (bakeriana nimia) alone provides 31.2 per cent of 

 this amount. Amnicola and J'alvata represent 59.3 per cent of 

 the total molluscan life. EUipiio complanatus is the most 

 abimdant mussel, representing 93.3 per cent of this class of 

 mollusks (see figures 39-41). The absence of Physa and the 



