Fishery bulletin of the Fish and Wildlife Service - NOAA

374 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
number of undersized whitefish per lift (as determined from our observations in the
field). Estimates were made separately for large-mesh (4 inches and greater) and
small-mesh (less than 4 inches) nets and combined to obtain the totals listed in the
table. It .was necessarily assumed that the relative numbers of large-mesh and small-
'mesh nets in the general fishery were the same as those observed by our investigators
in the field. Estimates were made of the capture and destruction of illegal-sized
whitefish by deep trap nets in H-5 in both 1932 and 1933, although field observations 38
were made only in 1932. The computations for 1933 (based on the assumption that
the abundance of young whitefish and the relative numbers of large-mesh and smallmesh
nets were the same in that year as in 1932) were carried out merely to provide a
rough idea of. the large numbers of whitefish that probably were handled during the
years of intensive fishing in southern Lake Huron.
The estimated numbers of young whitefish handled by pound-net and deep-trapnet
fishermen in the various districts and years were large (130,000 to 616,000). The
estimated destruction, however, appeared to be relatively small (4,600 to 21,700). The
combination of the data for all districts and years indicates a loss of 2.8 percent of all
undersized whitefish taken in pound nets and of 3.4 percent of those captured by deep
trap nets. These figures should not be taken as indicative of the percentage loss of the
total population of undersized fish (of the sizes handled) as many fish may have
been captured more than once and others, doubtless, were not captured at all.
Estimates were made also of the loss of small whitefish in the entire lakes (Michigan
waters) in 1932, the year of our most extensive field observations. The 1932
pound-net yield in districts H-2 to H-5, inclusive, amounted to 43.5 percent of the
catch of whitefish in pound nets in the entire lake. The "known" destruction of whitefish
by pound nets in these districts in 1932 amounted to 5,100 individuals (table 46).
If the average conditions of the pound-net fishery (abundance of young fish on the
grounds and relative numbers of large-mesh and small-mesh nets) in H-l and H-6 are
assumed to have been similar to those of the fishery in H-2 to H-5, the "known" destruction
of undersized whitefish in the pound nets-of all Michigan waters of Lake Huron
in 1932 can be calculated as 5,100/0.435 or 11,700 fish. Similarly, the deep trap nets
of districts H-2 to H-5 accounted for 93.8 percent of the total deep-trap-net catch
and for the estimated destruction of 20,600 young whitefish. The estimated "known"
destruction for all six districts was, therefore, 20,600/0.938 or 22,000 fish. The combined
"known" destruction of pound nets and deep trap nets in Lake Huron in 1932 was
33,700 whitefish.
The same calculations for the Michigan waters of Lake Michigan showed that in
1932 districts M-2 and M-3 yielded 52.1 percent of the total catch of whitefish in pound
nets and 76.5 percent of the deep-trap-net production. These percentages applied to
the figures on "known" destruction in table 46 yielded the following estimates of the
loss of undersized whitefish in all eight districts: pound nets—6,100; deep trap nets—
11,600; pound nets and deep trap nets—17,700.
The estimates of the "known" destruction of undersized whitefish by deep trap nets
in all Michigan waters of Lakes Huron and Michigan in 1932 (22,000 and 11,600 individuals,
respectively) can not be termed large. If that gear was extremely harmful to
the stocks of small fish the loss must have occurred through the death of fish that were
killed or injured fatally in the sorting of the catch.
The opinions of the fishermen concerning the ability of the whitefish to withstand
handling were found to vary M'idely. Some (particularly those who were opposed .to the
use of deep trap nets) contended that whitefish are extremely delicate—that they are unable
to survive removal from the water for even short periods of time and will die as the
result of the least amount of handling. Others (especially deep-trap-net fishermen) held
that the whitefish is exceptionally hardy—that with only reasonable care very few or none
at all are injured during the sorting of the catch.
Data are not available to show which of the above v diametrically opposite viewpoints
is the more nearly correct. However, the fact that 101 or 22.1 percent of 457
•» The pound-net fishery for whitefish waa negligible in H-5 in 1932 and 1933 (appendix B). Our investigators observed no pound-net lifti in
this district. .