WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 377 



6. A detailed analysis of the fluctuations in the production and abundance of white- 

 fish 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 bathymetric 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 rela- 

 tively more severe 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-trap- 

 net 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 un- 

 reasonable 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 dis- 

 trict. 



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^. 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 percent- 

 age 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^, 7; H-5, 5; H-6, 10. These figures dem- 

 onstrate 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 



