370 ILLINoIs NATURAL History SURVEY BULLETIN 
desirable size, and all evidence of over- 
fishing would have disappeared. 
In comparing the average size of the 
fish caught and the catch per man-hour 
from this lake, while it was overfished, 
with catches from several underfished 
waters, a striking similarity was found. 
In both, the catch per man-hour was low. 
In both, a very large per cent of the fish 
caught were small. It is little wonder 
that the average fisherman confuses under- 
fishing with overfishing. The relation be- 
tween size and age in fishes is the best 
criterion for judging the status of a pop- 
ulation. For example, scales from 6-inch 
bluegills taken from an overfished lake 
show that the fish were less than 2 years 
old. Scales from bluegills of the same size 
taken from underfished lakes typically 
show from four to six annual rings. Lay- 
men can often distinguish between fish 
from an overpopulated lake and an under- 
populated lake by the fact that those from 
the former are usually thin bodied, have 
large heads and unusually prominent eyes. 
Experimental Combinations of Fish 
The meagerness of hook-and-line fishing 
furnished by many unmanaged artificial 
lakes leaves little doubt as to the necessity 
of proper management for the production 
and maintenance. of good fish yields. The 
more common causes for poor yields are 
summarized as follows: 
1. Indiscriminate stocking—the intro- 
duction of fish physiologically unsuited to 
the artificial lake habitat or those of little 
or no angling value. 
2. Undesirable populations — those in 
which rough fish or other species not use- 
ful in fishing make up a large part of the 
populations and compete with the hook- 
and-line species. 
3. Overpopulation — as in lakes con- 
taining only desirable fish but so densely 
populated that stunting results, which in 
turn means poor fishing. 
All of these causes may be controlled 
in small artificial lakes, or in large lakes 
that can be drained. 
Lakes controlled by fishing clubs some- 
times produce good sustained yields of fish 
but, although the yearly crop and the catch 
per man-hour remain at satisfactory levels, 
there are great fluctuations in the abun- 
dance of the various species from year to 
Vol. 227A thas 
year. To fishermen who have preferences 
in fishing, these fluctuations are perhaps an 
annoyance. The study made by Thompson 
(ms. unpublished) of the catch records of 
Rinaker Lake near Carlinville illustrates 
the extent of these variations. In Rinaker 
Lake, where complete catch records are 
available from 1932 to date, the important 
species are largemouth bass, white crap- 
pies, bluegills and bullheads. The catch of 
bluegills remained most nearly constant 
throughout this period of years, at 1.25 to 
2.25 pounds per fisherman-day. Good 
catches of bass were made from 1932 
through 1936, and the crappie catch was 
poor for these years. In 1937 the catch of 
crappies reached an all-time high of 2.5 
pounds per fisherman-day, and the catch 
of bass was very low (less than 0.25 
pound per fisherman-day). Since 1937 
the bass catch has been steadily improving 
and that of crappies decreasing. Bullheads 
have remained at a low population level 
throughout all years, but individuals 
caught are of exceptionally large size. “The 
total hook-and-line yield for this lake has 
averaged about 4 pounds per fisherman- 
day and 100 pounds per acre per year 
during this period. 
A more or less constant yield of blue- 
gills, with large fluctuations in catches of 
crappies, bass and bullheads, seems to be 
typical of lakes containing these species. 
Usually, however, when crappies or bull- 
heads reach their peak of abundance they 
are not taken in sufficient numbers to pre- 
vent stunting and to give bass an oppor- 
tunity to make a “comeback.” Fluctua- 
tions of this kind make fishing for selected 
species uncertain. In lakes such as Rin- 
aker, the fish manager should attempt to 
control the size of broods of young fish 
produced each year, with the object of 
maintaining a more nearly uniform pro- 
portion among the different species. 
The great seasonal variation in the suc- 
cess of fishing for a selected species in lakes 
containing many kinds of fish has led to 
experimentation with single species and 
simple combinations of more important 
fish. In the stocking of many new ponds 
and several large reservoirs in Illinois, an 
attempt is being made to discover some 
means of maintaining good bass fishing. 
The combination of largemouth bass and 
bluegills has the following points in its 
favor: 
