464 
the same year the river between Copperas Creek dam and Lagrange dam, 
where the lake acreage is largest relatively to the total, should have 
furnished about 10% of the total fish yield; the river between La Salle 
and Copperas Creek dam, about 17%; and the river below Lagrange, 
about 37%. That the river and lake yields of fish per acre are not equal, 
however, is suggested with considerable force by more than one consid- 
eration. The first of these is the fact that in all the recent years for 
which we have records the largest poundages of fish per acre have been 
taken in the reaches with the largest quotas of connecting lake-acreage. 
Taking the year 1908 as an illustration, and using the figures for sep- 
arate shipping points obtained by the Illinois Fish Commission in that 
year, we find for the 59.3 miles of river and lakes between Copperas 
Creek dam and Lagrange dam, with about 90% of its acreage consisting 
of lakes and ponds, an average fish-yield per acre for water levels pre- 
vailing half the year, of 178.4 pounds; for the.87 miles from La Salle 
to Copperas Creek dam, with about 83% lakes, 130.4 pounds; and for 
the lower 77 miles, Lagrange to Grafton, with around 63% lakes, only 
69.8 pounds. 
If, again, we seek to reach conclusions concerning fish vields for 
the central Illinois Valley district from the bottom- and shore-fauna 
data of 1914—1915 we can only suppose that the average yield of the 
river per acre in recent years between the Copperas Creek and Lagrange 
dams (with 705 Ibs. bottom fauna average) has amounted to less than 
half the average yield of the lakes opposite (with 1,447 + lbs. bottom- 
and weed-fauna average). Or, to put it another way, while the river’s 
quota of the total fish catch in this reach on a plain acreage basis in 1908 
was 10%, its capacity on a basis of the bottom- and shore-fauna figures 
of 1914—1915 uncorrected, stands at about 5% of the total. ; 
That both the river and the lake yields of fish per acre have been 
lower in recent years in the reach above Copperas Creek dam and in the 
reach below Lagrange than in the district between, is suggested both by 
our bottom-fauna data from the river and by such incomplete figures as 
we have from Peoria Lake and Meredosia Bay (1913 and 1914), and 
also by the fact that the differences in fish yield per acre in 1908 between 
those two reaches and the Havana section are much greater than the 
difference in the ratios of lake to total acreage. That, however, the per 
cent. decrease in fish-yield in the lakes in these two reaches is less than 
the decrease in the river may perhaps be accepted as circumstantially 
proven by the greater decrease in the river bottom-fauna figures than in 
the figures of fish yield themselves. 
