Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 309
and other changes in fishery regulations can have a profound if undeterminable effect
on total yields.
Production may vary according to general economic conditions. In periods of
depression low prices may render operations unprofitable and thus bring about a
curtailment of fishing activities. On the other hand, an economic depression has
been observed in at least one industrial district to have the reverse effect of stimulating
fishing intensity. Here numbers of unemployed turned to small-scale fishing as
an emergency source of income—meager, to be sure, but preferable to none at all.
Other factors, such as weather conditions, might be listed which cause fluctuations
in production that are independent of the level of abundance of the stock. However,
those mentioned are sufficient to bring out the difficulties inherent in the use of catch
statistics for the estimation of changes in the abundance of fish, particularly over
long periods of time.
Despite the limitations just outlined, there is good reason to believe that under
normal conditions (without disruption in the methods or regulations of the fishery),
over limited areas, and for short periods of years, large increases or decreases of
production may serve as reliable indicators of increases or decreases in the abundance
of fish on the grounds. The changes in annual yields do not measure the changes
in abundance, but merely indicate their occurrence. This view concerning the general
relationship between the production and abundance of fish has grown from the careful
examination of records that have been maintained, beginning in 1929, of the
annual fluctuations in the catch and abundance of fish on the grounds and in the
intensity of the fishery for all commercially important species in 21 fishing areas of
the State of Michigan waters of the Great Lakes.
Ordinarily fluctuations in production exceed those in abundance; that is, the
increases in the catch tend to be relatively greater than the increases in abundance
when the latter rises above the average, and conversely, the decreases in the yields
tend to be greater than the decreases in abundance when the latter falls below the
average. As a result the curves of production often are "exaggerations" of the curves
of abundance. This general relationship between abundance and catch has its origin
in the circumstance that fishing intensity tends to be above average when abundance
is above average and below when abundance is below. Of course, exceptions occur
in the relationships outlined above but these exceptions do not affect the general
validity of the statements. 14
Among the increases in production that safely may be held to reflect (but not
measure) a greater abundance of fish on the grounds are those that occurred in the
catch of whitefish in Great Lakes waters near the beginning of the 1930's. Although
the actual years of high yields varied somewhat in the different waters, an increase
occurred in every important center of production. The increase in the catch was relatively
greater in the State of Michigan waters of Lake Huron than in other areas.
The extent to which the recent increase in production was relatively greater in
the State of Michigan waters of Lake Huron than in other areas may be brought out
•by comparisons of the take in the 2 or 3 recent years of greatest yield with the
average catch over a period of earlier years. The average production in the peak
years, 1931 and 1932, was 3.67 times the average for the years 1889 and 1891-1929.
This value is considerably higher than the ratios for other areas as the following
tabulation shows:
Huron (Stute of Michigan)
Huron (Province of OnUrio-Hurc
Huron (Province of Ontario-Qeor
Michigan (State of Michigan)
Arca
Years of
early
period
1889, 1891-1029
1893-1932
1895-1932
1880, 1891-1926
1889-1927
1911-1930
Ш1-192Т
.Years of
recent
period
1931-1932
1933-1935
1933-1935
1929-1930
1929-1931
1031-1933
1929-1931
Ratio of
recent to early
production
и See part II for a diacuaaion of the relationships among the fluctuations in the production and abundance of whitefish and in tte intensity of
the whitefish fishery in Lakes Huron and Michigan.
3.67
2:86
1.26
2.38
2.58
1.97
1.68