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v 
Ittinois NatrurRAL History SurveEY BULLETIN 
Vol. 26, Art. 2 
Fig. 12.—T aking a sample of scales from largemouth bass handled in Ridge Lake draining 
census. 
Scales collected from bass and bluegills taken in draining censuses or caught by 
anglers were placed in small envelopes and later used for aging these fish. 
removed from the lake at 2-year intervals, 
selection would have been continuously 
in favor of the rapidly growing fish. How- 
ever, in each year the lake was drained, 
some small bass remained in the lake basin 
and survived by staying either within the 
blind end of the old stream channel near 
the dam or in undrainable water pockets 
that appeared in the lake bottom as a 
result of uneven deposition of silt. After 
water was again impounded behind the 
dam, these bass escaped to mingle with 
the population of selected fish that were 
returned to the lake. Probably many of 
the escaped fish were eaten by the larger 
returned fish, but those that survived 
found conditions optimum for rapid 
growth. On the next census 2 years later, 
they made their appearance as the larger 
individuals of the group of unmarked fish. 
During the period 1941-1951, scale 
samples, fig. 12, were collected from 4,305 
bass that were taken by fishermen or that 
were returned to the lake following drain- 
ing censuses. Later these bass were aged 
and separated into broods (year-classes). 
Growth curves were constructed for the 
individual broods by use of the average 
lengths of the fish at the time of capture. 
The growth curves for 4,273 of these fish 
are shown in fig. 13. The numbers of 
fish in the year-classes represented in this 
figure are given here: 1941, 1,780 fish; 
1944, 96 fish; 1945, 580 fish; 1946, 286 
fish; 1947, 1,038 fish; 1948, 203 fish; 
and 1949, 290 fish. The 1942 and 1943 
broods were represented by only 17 and 
15 fish, respectively, too few for use in the 
construction of valid growth curves for 
these broods. Average lengths of 1941 
brood bass in 1942 were based largely on 
fish of legal length kept by anglers; there- 
fore the growth curve for the 1941 brood 
in 1942 is not truly representative. 
The evidence furnished by the 1942 
creel, the 1943 draining census, and fish 
samples taken by Natural History Sur- 
vey staff members in 1943 indicates that, 
even after drastic thinning in 1943, the 
1941 brood of bass dominated the fish 
