mw FP wo 
Fig. 4. -- A white crappie scale (greatly enlarged). The number of rings or annuli on the scale de- 
note the age of the fish. Five annuli (denoting approximately 5 years of growth) are shown. Vertebrae 
and spines are used in aging catfish and bullheads. 
time of departure, and retains his state fishing 
license. When the fisherman returns to the boat 
yard, the liveryman checks the catch, records it 
and the time on the permit card, and gives back the 
state fishing license to the fisherman. 
Through the splendid co-operation of the boat- 
yard operators and the anglers, the permit system 
has enabled us to obtain fairly accurate statistics 
on the yield of the sport fishery of a large bottom- 
land lake of the Illinois River system. 
On many week-ends, fish caught by anglers 
were weighed and measured by the authors. Scale 
samples were taken from many of the fish for later 
age determination, fig. 4. 
In the late spring and summer months, minnow 
seine hauls were made along the lake shores to 
determine the annual spawning success of the 
various fish found in the lake. Also, young fish 
were collected with a small trap net. In 1951, rote- 
none was used to poison the fishes in one small 
bay of the lake, 1n order to test the efficiency of 
fishing gear in taking small fishes and to sample: 
any species that were missed in minnow seining. 
In each of the two falls, 1-inch-mesh wing: 
nets with leads were set at designated stations., 
These nets, which caught samples of the larger: 
fishes, were particularly useful in determining size: 
distribution of crappies and other species. 
Crappies (7 inches or larger) caught in these: 
netting operations were released after being 
marked, each by a numbered tag fastened to one of! 
the gill covers. This method of marking fish is: 
shown in fig. 5. Recaptures of marked crappies: 
allowed us to estimate the population, to calculate: 
the rate of exploitation of these fish by fishermen, 
and to acquire some information on fish movement. 
Records were made of the sport fishes taken 
by commercial fishermen in seine hauls and in 
wing nets fished in the lake. The catches often 
ptovided examples of unusually large sport fish) 
not ordinarily appearing in anglers’ catches or in| 
our small-mesh net sets. 
