342 
In comparing the efficiency and selectiv- 
ity of the various entrapment devices, it 
was necessary to consider the average 
size of the fish taken, as well as the num- 
ber of commercial-sized or desirable-sized 
fish caught. A small-mesh net might take 
as many fish of commercial species as a 
large-mesh net; however, the catch of the 
7 
FISH PER NET DAY 
HOOP NET 
|-INGH MESH 
WING NET 
I-INCGH MESH 
NO LEAD 
Ittinois NATURAL History SuRVEY BULLETIN 
WING NET 
2 1/2-INCH 
MESH 
Vol. 26, Art. 4 
small-mesh net might be largely of fish 
under commercial size. The large-mesh 
net taking only a few fish under commer- 
cial size would be a more efficient net to 
the fisherman since it would require less 
time for the handling and releasing of 
small fish. 
The mean of the total lengths of indi- 
COMMERGIAL FISHES 
HM SPORT FISHES 
PREDATORY FISHES 
FORAGE FISHES 
“HOOP NET 
2 \/2-INCGH 1 1/4-INGH 
MESH MESH 
Fig. 12.—The number of fish, all sizes, taken per net-day in entrapment devices fished in 
the Mississippi River between Burlington and Dubuque in 1946. 
Table 6.—Data (from table 13) on catches of wing nets of two different mesh sizes used in 
fisheries survey of the Caruthersville-Dubuque section of the Mississippi River, 1944, the data 
selected and presented to allow comparison of the sizes of carp taken by the two mesh sizes. 
Mean Tora 
TANDARD 
LENGTH (x), s 
DeviaTION (s) 
NuMBER OF 
Carp (n) 
INCHES 
14.47 886 3.34 
14.96 356 phy 
The following equations are based on the t-test for significance and the degrees of freedom 
(d.f.) formulas on page 344. 
14.96 — 14.47 0.49 
(2.37)? (3.34)? V 0.2839 
\ 356 886 
d.f. = V 356 - 886 
= 2.908 
— 1 = 561.6 or 562 — 1 = 561 
