Ee) 
oA YH 
AN 
We 
B. vf : 24. 
NOTURUS fienry PERCINA 
miURUS ee, a MACULATA 
eams in western Illinois because of runoff from hog 
ms, and the West Branch of the Salt Fork because 
sewage effluents from Champaign-Urbana. 
Fish kills have occurred repeatedly when toxicants 
+h as anhydrous ammonia and cyanide have been 
‘identally or deliberately dumped into streams. 
most cases the streams are repopulated in 2 or 3 
us, but endemic and relict species cannot return 
e the population has been eliminated. 
The revelation that water pollution ranks fifth 
ong the principal causes for extirpation and decima- 
1 of native fishes is rather surprising. However, 
ny fishes are remarkably resistant to some degree 
pollution as long as the physical habitat remains 
ct. Also, in many parts of Illinois, pollution has 
ome critically severe only in the last few years, 
reas other factors have been Operative for a 
tury or more. 
ns and Impoundments 
[he construction of dams to create mainstream 
oundments ranks sixth and is responsible for the 
mation of four species of riffle-inhabiting fishes. 
flowing stream consists of alternating riffles and 
s. Riffles may flow over bedrock, boulders, rubble, 
el, or sand, and each bottom type comprises a dis- 
ive habitat. Pools also may have different habitats, 
nding on the type of substrate and current. When 
fam is impounded, riffles are eliminated and the 
m of the reservoir quickly becomes silt, resulting 
nly one habitat. The richness of the fish fauna 
rectly related to the number of different habitats 
able. Dams also block natural migration and dis- 
U of fishes. 
he greenside darter (Fig. 25), eastern sand darter 
26), fantail darter, and dusky darter have been 
Faget ee DAL) ei 
ee Rae bb PDA 
ih 
Fig. 23-24.—Two species of fishes deci- 
mated because pollution has lowered the 
water quality of streams that they in- 
habited. Circles, before 1905; dots, after 
IVEY 0). 
decimated in the North Fork (Vermilion drainage ) 
and Embarras River by mainstream impoundments 
(Smith 1968). The bullhead minnow is now re- 
stricted to that part of the Embarras River below the 
Charleston dam but once occurred farther upstream. 
The effects of dams on the fishes of the Mississippi, 
Illinois, Kaskaskia, and Rock rivers are more difficult 
to document, but the dams are insurmountable to 
migratory fishes except when the streams are in flood 
condition, and many miles of stream that formerly 
contained several distinctive habitats now have only 
one, 
The several proposed reservoirs in linois threaten 
many native species because they are planned for 
some of the most valuable waterways left, and many 
of the unique aquatic habitats in the state will be 
lost if the streams are dammed. 
Temperature 
The cutting of marginal trees and other vegetation 
that afford shade, coupled with a reduced flow of 
cold springs and low water levels during summer 
droughts, result in higher water temperatures now 
than formerly. No data on past stream temperatures 
are available, but temperature offers the most likely 
explanation for the disappearance of the northern 
pike in streams of western Union County, where it 
occurred prior to 1900 (Forbes & Richardson 1908, 
atlas of maps). 
Outlier populations of such species as the horny- 
head chub, blacknose dace, longnose dace, redbelly 
dace, and hogsucker in Union County have also been 
eliminated, probably because they cannot survive the 
summer stream temperatures. However, in other areas 
of the state their decimation is more likely the result 
of stream desiccation and siltation. 
13 
