S72 
ly numerous. The growth of bass was 
about average for most Illinois waters, 
eas 
‘The hook-and-line catch in Fork Lake 
was 2.84 fish per man-hour in 1939; 3.23 
fish per man-hour in 1940 and 2.98 in 
1941. This catch was made up almost ex- 
clusively of bass, as artificial baits having 
hooks too large for bluegills were com- 
monly used. The figures on catch per man- 
hour are based on both illegal and legal 
bass, as all were kept. The maximum 
catch was made in April, 1940, when 27 
small bass were taken in 2 man-hours of 
fishing. 
Previous to the removal of rough fish 
and bullheads in 1938, Fork Lake was 
very muddy and devoid of aquatic vege- 
tation. When these fish were removed and 
replaced by bass and bluegills, the water 
cleared and remained clear, and after a 
few weeks the water weed, Potamogeton 
foliosus Rafinesque, appeared. This weed 
spread during 1939, 1940 and 1941, until 
it formed dense mats in all shallow water 
up to 5 feet in depth. These dense tangles 
Ittino1is NATURAL History SURVEY BULLETIN 
Vol. Ze; Aries 
of coarse vegetation offered excellent pro- 
tection for young bluegills, but very little 
food. During the summer of 1941 when 
this vegetation was most abundant, small 
bluegills and bass of all sizes grew slowly 
because large numbers of young bluegills 
swarmed in the plant mats, but found little 
nourishment, and the bass were unable to 
use them for food. However, in August 
the weed practically disappeared within a 
few weeks and almost concurrently the 
bass became very fat, probably through 
assimilation of the gverabundant small 
bluegills. 
Higher aquatic plants are a detriment 
to small artificial lakes in that they pro- 
mote the survival of too many young fish, 
fig. 6, and during their growing season 
they take up nutrient materials and light 
that would otherwise produce algae, the 
basic food of the aquatic environment. 
On July 8, 1942, the Fork Lake experi- 
ment was suddenly terminated by abnor- 
mal precipitation. On this date, a rain of 
approximately + inches caused the dam to 
break near the center, and a part of the 
Fig. 5—Largemouth bass and bluegills from Fork Lake, near Mount Zion, Ill., April, 1941, 
showing 1938 brood bass and 1938, 1939 and 1940 brood bluegills. 
