Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 323
with average conditions in 1891-1908, evidence that the 1929 percentage for the district
did not represent an abnormal condition, may be seen in the fact that the catch in H-4
exceeded that in H-l in 6 successive years (1898-1903) of the 18 in the: early period.
The percentage of the Lake Huron catch produced in H-4 in 1929 apparently .was
somewhat above the average for the modern as well as the early period, as in thç
9 years, 1920-1928, the percentage of whitefish taken in Saginaw Bay (in H-i) did
not exceed 31.3 percent and averaged only 23.5 percent. (This statement is based on
statistics published for Saginaw Bay and Huron proper by the Michigan Department
of Conservation.)
The evidence that the percentages of the 1929 yield of whitefish taken in the
several districts were within the normal range of variation lends further support to
the belief that the deep-trap-net fishery brought about abnormal conditions in' 1930-1939.
CHANGES IN PRODUCTION IN LAKE HTJBON AS RELATED TO
FLUCTUATIONS IN THE ABUNDANCE OF WH1TEFISH
AND IN THE INTENSITY OF THE FISHERY
Up to this point the discussion has been concerned only with the fluctuations in
the catch of whitefish, because it was believed that this, the more obvious phase of
the fishery, should be outlined clearly before the changes in production were analyzed
in relation to concurrent fluctuations in the abundance of whiteush and the intensity
of the whitefish fishery. The fundamental problem in the analysis of the statistical
data relative to the whitefish fishery of Lake Huron is the determination of the probable
effects of deep-trap-net operations on the abundance of marketable whitefish.
As pointed out previously (p. 315) this problem is complicated greatly by the circumstance
that whitefish are known to have been abnormally abundant during the
years in which the deep-trap-net fishery was undergoing its most rapid..expansion.
The abundance of whitefish in Lake Huron was possibly above normal in 1929; certainly
it was well above normal in 1930 and 1931 (table 10). A decline from this
abnormally high abundance would have occurred even if deep trap nets had not been
operated in the lake. It is only logical to believe also that the high abundance following
1929 would have stimulated fishing intensity even had deep trap .nets not been
fished. The general problem resolves itself, therefore, into the estimation of the degree
to which the increased fishing intensity and the heightened production made possible
by the use of deep trap nets affected the rate of the decline in abundance and its ultimate
extent. I
That the deep trap net accounted for the bulk of the extremely high yields of
whitefish over the period, 1930-1935, was brought out in the preceding section. It
will now be demonstrated that the high production resulted from an unreasonably
great fishing intensity and that this overfishing in turn accelerated the decline in the
abundance of whitefish. In the four southernmost districts in which the deep trap
net was fished most extensively the whitefish fishery reached a state of collapse.
Abundance and catch were reduced in the other two districts in which the deep-trapnet
operations were less extensive but the decline was far less pronounced than in the
four districts.
A comparison of the extent of the changes in production, abundance, and fishing
intensity in the several districts may be found in table 7. In this one table the year 1929
rather than the 11-year period (1929-1939) has been taken as the point of reference.
To be sure, there is no certainty that 1929 was a "normal" year. However, the catch
in 1929 was at approximately the typical level for 1922-1929, and there is no evidence
of any unusual conditions in the fishery in that year. Certainly, 1929 is the most
nearly normal year for which detailed statistical data are available.
The data of table 7 do not provide a complete history of the deep-trap-net fishery.
They do serve, however, to show the variation among the districts in the maxima of
yields and fishing intensity that followed the introduction of the deep trap net, and
the apparent relationship between these maxima and conditions in 1939. The increases
in catch were by no means as great in: H-l and H-2 as in the remaining districts. In