most damaging in southern, western, and central Illi- 
nois. During severe droughts, swamps, springs, creeks, 
and even small rivers have dried up. 
Species Interaction 
Species interaction following modification of a 
stream or watershed ranks fourth and is responsible 
for the extirpation in Illinois of the Ohio lamprey and 
the rosefin shiner and the decimation of seven other 
species. Prior to 1917 the Ohio lamprey occurred in 
the Wabash watershed, but the allied and allopatric 
chestnut lamprey has since supplanted the Ohio lam- 
prey in all of eastern Illinois and western Indiana (Star- 
rett, Harth, & Smith 1960). The rosefin shiner occurred 
in extreme southeastern Illinois in the last century but 
has been supplanted in Illinois and adjacent Kentucky 
by the more ecologically tolerant and allopatric redfin 
shiner. 
In addition to competition between members of a 
pair of closely related fishes, there have been inter- 
actions unrelated species that resulted in the decima- 
tion of several native species. The explosive appear- 
ance of the sea lamprey in Lake Michigan in the 
1940’s was followed by a dramatic decline in popu- 
lations of the cisco, lake whitefish, round whitefish, 
lake trout, and burbot. When the ecological balance 
was upset by sea lamprey predation, the alewife ap- 
peared and mushroomed in numbers to become a seri- 
ous pest in Lake Michigan. 
The aggressive and ecologically tolerant red shiner 
has gradually moved eastward in Illinois (Larimore 
& Smith 1963) and has displaced the related spotfin 
shiner (Fig. 21), and steelcolor shiner (Fig. 22) in 
most parts of central Illinois (Page & Smith 1970). 
Habitat modification evidently resulted in a break- 
down of the reproductive isolating mechanisms in 
ory MeN 
BIDEN 
Vane ee! 
this group of species and permitted the red shiner tc 
hybridize with and eventually replace the other two 
species. 
Such species interactions have been in progres: 
for a long time and throughout the state. The effect 
on certain native fish by the introduced carp anc 
goldfish are so well known that no comment is re 
quired. More recent stockings of the white amu 
redear sunfish, mosquitofish, white catfish, and salmoi 
species outside their natural ranges may pose equall 
serious threats to native fish populations in the future 
Pollution 
Pollution other than silt includes industrial, dome: 
tic, and agricultural pollutants and ranks fifth. It can b 
implicated as the cause for the extirpation of two an 
decimation of five fishes. The greater redhorse 0¢ 
curred in Salt Creek in northeastern Ilinois but di 
appeared sometime after 1901 when the stream bi 
came polluted. The cypress minnow occurred in th 
Little Muddy River as late as 1940 and was eliminate 
by pollution, presumably from nearby oil fields. 
The ranges of the silver chub, river shiner, brindle 
madtom (Fig. 23), bluebreast darter, and blacksic 
darter (Fig. 24) are less extensive than former 
because of localized pollution in several stream sy 
tems in eastern and southern Illinois. 
Virtually all of the streams and lakes in IIlinc 
have been affected to some degree by pollutio 
Among the most dramatic illustrations are strear 
and lakes in the greater Chicago area because 
industrial and domestic pollution, the Big Muddy ai 
lower Little Wabash systems because of oil-fie 
pollutants, the Illinois River because of domes’ 
sewage from Chicago and other cities, most of t 
Saline system because of coal mine wastes, sm 
aD 
Fig. 21-22.—Two species of fishes 4 
Ey 
x] oe 
se: YR oz 
@ Pod : 
Ve: eae a if mated because they were unable to ¢ 
me PE vies os aec sel " pete with the related red shiner al 
aweeure A their original habitats had been alte! 
AG pe Reser < Circles, before 1905; dots, after 1950. 
esiVee gS 
©, PHY Ve yD es) 
BON ATL 
Pasa 
Rasy 
Sees 
a n | | SPR 
MSPILOPTERUS MWAIPPLEL PS. 
12 
