February, 1943 
1. Both species are well suited to the 
artificial lake habitat and are much sought 
by anglers. The largemouth bass is Illi- 
nois’ most important large game fish, and 
the bluegill is a favorite pan fish with fly 
fishermen. 
2. The bluegill is very prolific and 
spawns throughout the summer. Enough 
young are produced to maintain an ade- 
BENNETT: MANAGEMENT OF ARTIFICIAL LAKES 
Syl 
hoopnets were fished for 1 week each 
month from March to November, in- 
clusive, during 1939, 1940, 1941 and part 
of 1942, and all fish caught were removed 
from the lake. Hook-and-line fishing was 
more effective than hoopnets in removing 
largemouth bass. The total yields for these 
years are shown in table 4. 
As the lake was cropped, no attempt was 
Table 4.—Fish yields from Fork Lake, near Mount Zion, Ill., 1939, 1940, 1941 and 1942.* 
BLUEGILLS 
YEAR Moral 
Number Weight, 
Pounds 
SOU) LO Ti es eae 940 eA 
OCT | re 778 146.2 
SEG 9) ke er 503 71.8 
ED ee eh rn 2535 SWE 
Total 2,474 427.9 
LarGEMOUTH Bass 
Average Total Average 
Weight, Number Weight, Weight, 
Pounds Pounds Pounds 
0.183 349 5120 0.146 
0.188 DAT 52:9 0.224 
0.145 185 Siieo 0.309 
0.148 40 Ze. 0.568 
791 183.9 
Combined yield—3,265 fish, weighing 611.8 pounds. 
* Cropped from March through June, 1942. 
quate population for angling, as well as to 
furnish forage for bass. 
3. There is little food competition be- 
tween these two species. Bass feed upon 
young bluegills, crayfish, adult aquatic and 
terrestrial insects and the nymphs of drag- 
onflies and damselflies; bluegills on ento- 
mostraca, midge larvae and aquatic vegeta- 
tion (particularly algae). 
4. The use of these fish allows lakes to 
remain clear, thereby increasing their rec- 
reational and aesthetic value. 
A yield study of the bass-bluegill com- 
bination was made at Fork Lake, near 
Mount Zion, Ill. The area of this pond 
during the past + years has varied between 
1.00 and 1.38 acres; the maximum depth 
from 7 to 9 feet, depending on the water 
level. “Iwo publications give in detail the 
results of investigations in 1938 and 1939 
(Thompson & Bennett 1939; Bennett, 
Thompson & Parr 1940). In 1938 the 
lake was poisoned because it contained 
many undesirable fish, and restocked with 
270 stunted adult bluegills and 1,440 
largemouth bass fry. No more fish have 
been placed in the lake since this restock- 
ing in 1938. Intensive cropping was begun 
in 1939, use being made of both hoopnets 
and hook-and-line fishing. Six 1-inch-mesh 
made to protect either bass or bluegills 
during the spawning season, and the lower 
size limit of the fish taken was controlled 
ordinarily by the mesh of the nets used. 
On some net raises, however, very small 
fish were trapped when the meshes _be- 
came bunched. A small number of blue- 
gills less than 2 inches long were caught 
in this manner. In 1941, the yield of blue- 
gills was smaller than in previous years, 
although the bass yield was somewhat 
larger. This small yield of bluegills in 
1941 was due in part to the poor survival 
of bluegill fry until late summer in 1939. 
During most of the bluegill spawning sea- 
son in 1939, young bass 5 to 7 inches long 
fed upon bluegill fry before they left the 
nests. A field observation on this point 
was verified by stomach analyses of many 
bass. 
Further analyses of the fish yields for 
these years show that 39.2 per cent of the 
bluegills taken in 1939 were of desirable 
size or larger (6 or more inches) ; 60.6 
per cent in 1940 and 38.4 per cent in 1941. 
Legal bass (10 inches or larger) made up 
0.85 per cent of the catch in 1939; 8.8 
per cent in 1940 and 29.5 per cent in 1941. 
The largest bluegill taken weighed 0.74 
pound, and half-pound bluegills were fair- 
