Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 327
In the previous section attention was called to the existence of a typical deeptrap-net
cycle of production (p. 319) in which the catch "was raised to tremendous
heights for about 2 years, only to fall away sharply." It is equally valid to speak
of "typical deep-trap-net cycles" of fishing intensity and in the abundance of whitefish.
(For graphical representations of the annual fluctuations in the catch and
abundance of whitefish and in the intensity of the whitefish fishery in the several
districts, see figs. 5 to 10.) The tremendous increases in yields were accompanied by
о
ï » г 9 1933 IS3S
CALCNDAR У E Л К
FIGURE 10.—Sixth district, H-8.
— I О О О
great increases in fishing intensity (table 8). To a large extent these increases in
intensity represented deep-trap-net operations (table 9). In about 2 years, however,
the fishing intensity declined in a district as the fishermen moved on to more productive
grounds. An exception to this cycle of intensity is to be found in H-6 where an
extremely intensive fishery was carried on for 5 years (1934-1938) despite a rapid
decrease in the returns. Operators of deep trap nets remained longer in H-6 because
the more northerly grounds had been exploited thoroughly in previous years (p. 321).
H-l and H-2 showed limited secondary increases in fishing intensity (about 1935-1937
in H-l and 1934-1935 in H-2) as some fishermen returned from the depleted grounds
in the south. .
Without exception the abundance of whitefish fell sharply after a period (usually
2 years) of intensive deep-trap-net operations. This fact is brought out clearly by the
data of table 10 in which the years of greatest production of deep trap nets have
been designated. (The comparison of tables 4 and 9 will reveal that the years of
greatest yields of deep trap nets and the years of greatest intensity of the deep-trap-net
fishery were not always the same.) .The nature of the changes in abundance that followed
heavy removals of whitefish may be .summarized for the districts as follows: .
H-l. Abundance began to decline in 1931, the second year of heavy production
by deep trap nets. This decline continued through 1933.
H-l
H-2
H-3
H-4
H-6
H-6
TABLE 8.—Annual fluctuations in the intensüy of the fishery for whitefish irijeach district of Lake Huron
District
1929
66
1S2
61
70 99
1930
94
246
250
940
IS
[Expressed as percentages of the average 1929-1939 intensity in the district]
1931
154
203
322
174 8
19
Fishing intensity as percentage of average in year
1932
129
114
153
264
84
16
1933
93
48
39
170
379
62
1934
92
65
50
70
192
. 168
1935
105
98
69
68
141
241
1936
130
54
67
44
118
172
1937
108
26
19
52
68
182
1938
70
40
67
52
53
172
1939
59
543
42
39
44