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 EH in 1929 apparently was 

 somewhat above the average for the modern as well as the early period, as in the 

 9 years, 1920-1928, the percentage of whitefish taken in Saginaw Bay (in H^l) 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 HURON AS RELATED TO 



FLUCTUATIONS IN THE ABUNDANCE OF WHITEFISH 



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 whitefish 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 prob- 

 able 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 cir- 

 cumstance 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; cer- 

 tainly 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 fol- 

 lowing 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 ulti- 

 mate extent. 



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-trap- 

 net 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 



