Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 333
the curve of total production in 1931 if од!у gill nets and pound nets had been in operation.
The deep-trap-net catch, however, changed the form of the curve completely.
This gear not only deprived the whitefish of its former temporary respite during the
period of habitation in deep waters, but actually exposed the fish to a far more severe
exploitation in- late summer than it had previously suffered at any season. From these
facts it is obvious that effective regulation of the deep trap net must include the reduction
of its catches on the deep-water grounds on which whitefisb congregate during late
summer.
The summer assemblings of whitefish that made possible the great effectiveness of
the deep trap net seemingly were not as dense in northern Lake Huron as in the central
and southern regions of the lake. In each of the four southerly districts the average
catch per lift of deep trap nets exceeded 400 pounds in one year and was more than
200 pounds per lift in 2 or 3 years (table 11). In the northern districts the greatest
average catch per lift of deep trap nets was 168 pounds in H-l and 142 pounds per lift
in H-2 (in 1930 in both districts). The relatively poor success of deep trap nets is the
more remarkable in H-l because that area under normal conditions had been an important
and in many, if not the majority of years, the leading center of whitefish
production in the lake. At any rate these small catches per lift account for the more
moderate use pf deep trap nets in H-l and H-2.
A final point that deserves consideration is the possibility that mass migrations of
whitefish may have played a role in the shift, from year to year in the center of the
deep-trap-net fishery. The failure of the grounds on which the deep trap nets first were
fished and the resultant necessity for opening up new areas gave an early indication of
the disastrous results to be expected from the unrestricted operation of this gear.
Deep-trap-net fishermen denied inost vigorously, however, that their activity had caused
any depletion on the grounds. They contended that the fish had not been caught but
that they merely had migrated to another area. They held further that in changing the
center of the fishery they were only following the movements of the whitefish population.
In support of their contention they stressed the argument that only mass migrations
could make possible such high production in southern Lake Huron (H-5 and H-6),
an area in which the catch of whitefish hadalways been small.
The assumption of a mass migration of whitefish proceeding in the same direction
year after year runs counter to all known facts concerning the habits of the species.
Nevertheless, the possibility cannot be denied that extraordinary conditions might bring
about unusual reactions on the part of the fish. The strongest argument against the
theory of mass migration lies in the fact that such an assumption is altogether unneccessary.
The heavy yield in southern Lake Huron in 1932 and later years was not
made possible, as fishermen contended, by the influx of white'fish from more northerly
grounds. The records of the catch of gill nets per unit of effort (table 11) prove that
dense concentrations of whitefish had been present on the offshore grounds of H-5 and
H-6 for years before the deep trap net was introduced. In fact, the catch of whitefish
per unit of effort of gill nets in H-5 exceeded that in every other district during the
four years, 1929-1932. The catch per unit of effort of gill nets in H-6 was greater than
that in any other district in 1933 and was second only to the catch per lift in H-5 in
1931 and 1932.
The large production of deep trap nets in H-5 and H-6 was made at the expense
of the reserve stock rather than of a population of recent migrants. The generally low
output of whitefish in southern Lake Huron prior to the introduction of the deep trap net
can be attributed to a low fishing intensity. Gill nets, comparatively ineffective gear
for the capture of whitefish, accounted for the bulk of the catch (appendix B). Apparently
the relatively few pound nets were fished either at the wrong localities or depths to
produce large quantities of whitefish. Actually, suitable localities for whitefish pound
nets are scarce in southern Lake Huron.
WHITEFISH FISHERY OF LAKE MICHIGAN, 1929-1939
The most'important difference between the histories of the whitefish fisheries of Lakes
Michigan and Huron, 1929-1939, lies in the relatively limited development of the deep-