Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 377
b. A detailed analysis of the fluctuations in the production and abundance of'whitefish
and in the intensity of the whitefish fishery in the different areas of the Michigan
waters of Lakes Huron and Michigan in the years, 1929-1939, with special reference to
the effects of the operations with deep trap nets. The methods of analysis are described.
c. A study of the bathymétrie distribution of whitefish of legal and illegal size in
order to obtain data on which to base recommendations for possible restrictions on the
depth of water in which deep trap nets may be fished.
d. Observations in the field on the fishing action of pound nets and deep trap nets
-particularly on-the extent of the destruction of undersized whitefish. The field work
was carried out in 1931 and 1932.
3. Although the fluctuations in the yield of whitefish in the various areas of Lakes
Huron and Michigan over the period, 1879-1939, were by no means the same, certain
general trends may be described. Production was high in all areas in the early years
of the period. Later declines brought the catch to a much lower, and in some waters
remarkably stable, level about which the production fluctuated for several decades.
A pronounced general increase in the yield of whitefish occurred in the late 1920's and/or
early 1930's. This increase was relatively greater and the subsequent decline was relatively
more seyere in the State of Michigan waters of Lake Huron than in other regions.
of the Great Lakes. Graphical representations of the history of whitefish production
in different areas of Lakes Huron and Michigan are given in figures 2 and 3.
4. The increase in the abundance of whitefish that occurred in the late 1920's
and early 1930's complicated greatly the problem of detecting the effects of deep-trapnet
operations on the whitefish fishery of the State of Michigan waters of Lakes Huron
and Michigan. This increase would have brought about a rise in both fishing intensity
and catch even had deep trap nets not been introduced. Furthermore, a decline from this
abnormally high level of yield and abundance was logically to be expected; the mere
occurrence of a decline could not be interpreted as the result of the use of deep trap nets.
5. Despite this difficulty, the following observations demonstrated conclusively the
disastrously harmful effects of extensive deep-trap-net operations on the stocks of
whitefish:
a. The regions in which the deep-trap-net fishery underwent its greatest expansion
(the four southernmost statistical districts .of Lake Huron—see fig. 4) suffered an unreasonable
multiplication of fishing intensity. In these districts of central and southern
Lake Huron (H-3 to H-6) the maximum yield of whitefish was 4.3 to 26.6 times the
1929 catch; the maximum fishing intensity was 3.8 to 42.1 times the 1929 intensity. In
the two northerly districts (H-l and H-2)—areas in which the use of deep trap nets was
much less extensive—the respective maximum productions were only 2.6 and 3.2 times
the 1929 catch; the maximum fishing intensity was 2.3 times'that of 1929 in each district.
b. In all districts of Lake Huron the introduction of the deep trap net brought
about a tremendous increase in the catch of whitefish. After about two years of high
production the catch fell sharply. This decrease in yield was accompanied by a rapid
decline in the abundance of whitefish. However, these declines were relatively greater
in central and southern Lake Huron. The 1939 production of whitefish, expressed as
a percentage of the 1929 catch, was 38 in H-l and 23 in H-2. These percentages were
only 1 and 5 in H-3 and H-4. In H-5 and H-6 the 1939 yields were only 19 and 46
percent, respectively, of the 1929 production despite fishing intensities that were 4.3
and 4.9 times those of 1929. The 1939 abundance of whitefish, expressed as a percentage
of the 1929 abundance, was 41 in H-l and 43 in H-2. In central and southern Lake
Huron these percentages were: H-3, 6; H-4, 7; H-5, 5; H-6, 10. These figures demonstrate
that whereas the whitefish fishery merely declined in those districts (H-l
and H-2) in which the use of the deep trap net was relatively moderate, it collapsed in
the districts (H-3 to H-6) in which deep-trap-net operations underwent their greatest
expansion. The excessive use of deep trap nets, therefore, may be stated positively to
be the cause of the present critical condition of the whitefish fishery in Lake Huron.
The severity of the depletion is illustrated by the fact that the 1939 production of only