February, 1943 
underfished, the total poundage of fish re- 
mains at or near the maximum carrying 
capacity of the lake. The fish are living 
on a subsistence basis and grow very slow- 
ly, if they grow at all. Frequently fish 
BENNETT: MANAGEMENT OF ARTIFICIAL LAKES 
369 
middle of the third summer, the remain- 
ing fish were censused by poisoning the 
lake. A comparison of this census with 
the theoretical pyramid of numbers indi- 
cates that overfishing removes the top from 
Fig. 4.—Onized Lake on the recreation grounds of the Owens-Illinois Glass Company near 
Alton, Ill. This lake, which produced a hook-and-line yield of nearly 350 pounds of fish per 
acre in 1939, represents the only overfished lake ever observed by the Illinois Natural History 
Survey. 
that are long enough to interest anglers 
are so emaciated that they are not kept 
when caught. Commonly, fish in these 
crowded lakes are about the same size as 
fish one-half their age in properly cropped 
waters. 
Although we have records of a number 
of lakes that have produced high fish 
yields, in only one instance do we have a 
complete story of overfishing. In this case, 
Onized Lake, fig. 4, the body of water 
was relatively small and the fishing in- 
tensity very heavy. During the 1939 fish- 
ing season the hook-and-line yield was al- 
Most 350 pounds per acre. Ihe’ yield 
study covered a period of two seasons and 
part of a third. The yield was very high 
during the first season, but lower and 
lower during the next two seasons. In the 
the pyramid, fig. 3. The census included 
a large number of fish, nearly all belong- 
ing to the three youngest age groups. 
Overfishing decreased the catch per man- 
hour as well as the average size of the fish 
caught, until few fish of desirable size were 
taken. The effect of overfishing on the 
growth rate of the population remaining 
at the time of poisoning is being deter- 
mined by scale studies. Apparently the 
young fish that had escaped the anglers 
were growing exceptionally fast. “These 
young fish were very numerous, suggesting 
that, as the population thinned, the sur- 
vival of spawn increased. None of the 
species present when intensive fishing was 
begun had been eliminated. Closing the 
lake to fishing for one season would have 
allowed many of these young fish to attain 
