Fishery bulletin of the Fish and Wildlife Service - NOAA

PART IV
OBSERVATIONS ON THE FISHING ACTION OF POUND NETS
AND DEEP TRAP NETS
EFFECT OF THE SIZE OF THE MESH ON THE CATCH OF LEGAL-
AND ILLEGAL-SIZED WHITEFISH AND LAKE TROUT
The question of the proper legal minimum size of mesh is a highly controversial
one that involves nearly all commercial fishing gears. Certainly the most desirable
size of mesh is that which releases the greatest number of illegal-sized and immature
fish without serious loss of legal-sized fish. However, a great diversity of, opinion
exists as to what this "desirable" size of mesh may be. Although there are a few exceptions,
commercial fishermen usually oppose most vigorously any attempt to increase
the legal minimum mesh size, and in practice generally fish the smallest mesh permitted
by law.
The lack of proper legal regulations and enforcement in the early years of the
deep-trap-net fishery led to a wide range of mesh size in .this gear. Many of the
early deep trap nets had meshes that were ridiculously small (as small as 2*4 inches,
stretched measure as fished) for a gear designed to take a species with a 2-pound
legal-size limit. Continued experience, however, led many deep-trap-net fishermen to
increase the size of mesh in their nets. This increase in mesh size not only reduced
the labor of sorting out the illegal fish and returning them to the lake, but also improved
the catch of legal fish as will now be shown.
The data in tables 36 and 37 on mesh selectivity in pound nets and deep trap nets
are based on comparison of the numbers of legal- and illegal-sized whitefish (2-pound
size limit) taken in nets with meshes less than 4 inches (stretched measure as fished)
and in nets with meshes of 4 inches and more. For convenience in the discussion, the
two groups of nets will be termed "small-mesh" and "large-mesh" nets. 38
Table 36 lists the total numbers of legal and illegal fish, the average numbers per
lift, and the percentages of fish of both size groups in all lifts of large-mesh and smallmesh
pound nets and deep trap nets observed in the course of the investigation. On
the average, small-mesh nets took more fish per lift, both legal and illegal, than did
large-mesh nets. The percentage of legal fish in the lift was higher (58.7 as compared
with 51.3) in large-mesh nets.
TABLE 36.—Comparison of total numbers, averages per lift, and percentages of legal and illegal whitefish
taken in amatt-mesh and large-mesh pound nets and deep trap nets
[The 1931-1932 data have been combined for all porto, all depths, and all months. Number» of lifta in parentheses]
Total number of whitefish taken
Item
•
Legal
Less than 4 inches
48,939
81.3
81.8
51.3
(598)
Whitefish taken in mesh
Illegal
46,441
77.7
77.7
48.7
Legal
4 inches and more
The unequal numbers of fish in the lifts of large-mesh and small-mesh nets make
a comparison of their selective action difficult. A better comparison is made possible
by the determination of the numbers of illegal fish that must be bandied in nets of
ы
In the original compilations the neta were grouped according to mesh siie by half-inch intervals. This grouping proved unsatisfactory, however,
since nets that fell within some intervals of mesh SÍEI were fished chieflv on grounds with an abundance of undersiied whitefish whereas the
nets of other mesh sites were fished predominantly on grounds where young whitefish were extremely scarce. In order to reduce irregularities from
this sonne, only two siie groups of mesh were employed in the preparation of data on the release of illegal-siied whitefish.
18,231
76.6
81.8
58.7
(2 38)
Illegal
12,820
53.9
57.6
41.3
365