July, 1955 
STarRETT & BARNICKOL: COMMERCIAL FisHinG DeEvIcEs 
343 
Table 7—Composition of catches made in 74 basket trap sets in fisheries survey of the 
Mississippi River between Cape Girardeau and Louisiana, Missouri, 1944. 
3 NuMBER OF ae WEIGHT Per Cent 
KinpD oF FisH Boe ees Wrasenne IN or Tora. 
G eee Pounps WEIGHT 
CoMMERCIAL 
2... RS ps Dal py) 4.0 
SIPERCHSH tae ee ee ee 18 24.7 8.70 13.9 
Mhemnelecathish.:.....!. oc... es ee ene 32 43.8 32.24 Sl7 
bene anicatlish........ ssc acs Des & 9 12.3 12.98 20.8 
recnwaterGrum:, . 25. .< os sens 1 1.4 0.75 12 
PREDATORY 
BIEROOSE Ab 6 2.5620 es wc seas eae 11 T5ed 5225 8.4 
LGGrih eS ie ee ee ae 73 100.0 62.44 100.0 
Table 8—Composition of catches of commercial-sized or desirable-sized fish taken in 
basket traps and in l-inch-mesh wing nets without leads in fisheries survey of the Mississippi 
River between Cape Girardeau and Louisiana, Missouri, 1944. 
Basket Traps a Wigeee tee 
(74.0 Nert-Days) (236. 5 Net-Days) Gan 
KinpD oF Fisu SQUARE 
Pounds Number} Pounds Number VALUE 
per |Number| per per |Number| per 
Net—Day Net-Day|Net-Day Net—Day 
ll oe = 0 — — 229 0.97 — 
Bigmouth buffalo.............. — 0 — — 4 0.02 — 
Smallmouth buffalo............ — 0 — — 12 0.05 — 
Freshwater drum.............. 0.01 1 0.01 0.53 171 0.72 Sle Al 
BmabMeueatish: 2. . 2.6.20 cee 0.34 16 0.22 0.26 31 0.13 2.60 
Seschead cathish.............. 0.09 Z 0.03 1.93 99 0.42 26.85* 
RE ee os ak os os — 0 = P| 0.09 — 
MOORE Geippic. ............... — 0 — = 187 0.79 — 
25S — 0 — — 249 1.05 _ 
* Denotes a significant difference, in numbers of commercial-sized or desirable-sized fish taken, between basket traps 
and 1-inch-mesh wing nets at 0.05 level with 1 degree of freedom. 
viduals of each species taken in each type 
of net was computed from measurements 
of all the fish of that species taken in that 
type of net. The actual total length of 
each individual was converted to the near- 
est one-half inch. The mean of the total 
lengths and the standard deviation of 
length of the individuals of a species taken 
in a particular type of net indicates ap- 
proximately the size of fish that can be 
expected in future catches of that net. 
The presence or absence of dominant year- 
classes of the various species would be ex- 
pected to change the species composition 
and the mean of the total lengths of indi- 
viduals in the catches from year to year. 
However, such changes would probably 
not materially affect the basic differences 
in efficiency and selectivity of the devices 
discussed here. 
Frequently the differences in the means 
of the total lengths of fish taken by two 
types of nets were not apparent. To de- 
termine whether the sizes of the indi- 
viduals of a species taken in one type of 
net were significantly different from the 
sizes of the individuals of that species 
taken in another type of net, a statistical 
test was desirable. The t-test, derived 
from a Snedecor (1946:81) formula 
adapted to groups with different numbers 
of individuals, appeared to be a satisfac- 
tory test for significance of size differ- 
ences of fish taken in two types of nets. 
The formula used in computing the t-test 
for significance is as follows: 
