46 
The sum of the various changes that have taken place in the small 
bottom-fauna of Peoria Lake since 1915, as shown in the summary tables 
next following, have not apparently affected average total valuation 
figures in pounds per acre since 1915 nearly as much as they have changed 
the composition of the fauna. In the upper lake, in fact, it appears that 
the 1920 figures, for all zones—in consequence principally of the enor- 
mous increase of midge larvae and sludge-worms since 1915—indicate 
total stocks slightly heavier than five years before. In the middle and 
lower lakes, however, average figures for all zones seem to have been 
cut at least in two when not divided by three, and an estimate of an aver- 
age reduction of around 50 per cent. in all zones of all three lakes com- 
bined would apparently be a fair approximation of the total change. 
It is, we believe, the losses in the shore and weed fauna, rather than 
those in the bottom animals, that have bulked greatest in Peoria Lake in 
the past few years. The loss in this element of the small invertebrate 
fauna of the lake has without question been almost a total one since 1915. 
The luxuriant growths of coarse aquatic plants (Potamogeton, Cera- 
tophyllum, Scirpus, Vallisneria, etc.) that covered several square miles of 
Peoria Lake at midsummer and autumn levels between 1910 and 1914, 
and their rich fauna of small invertebrates along with them have disap- 
peared now altogether in the upper and middle lake except for an occa- 
sional scraggly clump at the very edge. In the lower lake, a thin patch of 
Potamogeton and Ceratophyllum, covering less than two acres, was still 
growing in the small springy slough on the east side, opposite the foot 
of Liberty St., in August, 1920—the sole more than negligible remnant 
of the several hundred acres of vegetation in this part of Peoria Lake 
at low water five to ten years ago. 
Axtut SMALL BotroM-ANIMALS, CHILLICOTHE TO WESLEY, 1915 anp 1920 
AVERAGE VALUATIONS, POUNDS PER ACRE: SUMMARY 
1. Upper PrortA LAKE, CHILLICOTHE TO Spring Bay 
Channel 4—7-ft. zone 1-3-ft. zone 
1915 1920 | 1915 1920 | 1915 1920 
Viviparidae and Pleuroceridae| 317 0 87.5 0 50 72 
Sphaeriidae 76 56 87.9 12 6.2 12 
Amnicolidae, Valvatidae, ete. 0.8 0 0.1 0 | 8.5 0 
Chironomidae 0.2 182 4.2 128.6 | 1.8 0 
Oligochaeta ; 08 173 | 089 40 | 18 8 
Other insects, worms, | 
Crustacea, etc. ey ei) 0 3.9 0 Cae, 0 
Grand total _| 396.2 411 184.5 180.6) 75.5 92 
