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 stimulat- 

 ing 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 I 

 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 change? 

 in abundance, but merely indicate their occurrence. This view concerning the general 

 relationship between the production and abundance of fish has grown from the care- 

 ful 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 rela- 

 tively 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 trie average for the years 1889 and 1891-1929. 

 This value is considerably higher than the ratios for other areas as the following 

 tabulation shows: 



"See part II for a discussion of the relationships among the fluctuations in the production and abundance of white6sh and in the intensity of 

 the whitefish fishery in Lakes Huron and Michigan. 



