WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 315 



GENERAL REMARKS 



It does not come within the province of this paper to undertake a detailed criticism 

 of the statistical methods employed here, to discuss at length possible sources of system- 

 atic errors, to attempt to estimate the degree of reliability of certain necessary approx- 

 imations, or to explain the basis for the selection of methods followed over possible 

 alternative procedures. It can be said only that the methods employed for the analysis 

 of the statistics of the commercial fisheries of the Great Lakes have been developed 

 gradually from a careful study of extensive data covering all the commercially more 

 important species over a period of years and in a large number of different localities. 

 These methods have been adapted specifically to conditions in the Great Lakes. An out- 

 standing feature of the Great Lakes fisheries is that most species are taken in quantity 

 by several types of gear and that most types of gear take several species (usually simul- 

 taneously). These circumstances add greatly to the complexity of the problem of 

 analysis. 



No claims are advanced for the indexes of abundance and fishing intensity as 

 "precision measures" of the changes that occurred in the fishery. On the other hand, we 

 believe them to be sufficiently sensitive to bring out all changes of significant magnitude. 

 This belief is supported by the consistency with which conclusions based entirely on our 

 statistical data have been corroborated by reliable evidence gained independently from 

 other sources (interviews with fishermen; observations of field workers i. 



Although, as stated previously, a general criticism of our methods of analysis will 

 not be undertaken, it does appear desirable to call attention to certain difficulties of in- 

 terpretation peculiar to the statistics of the whitefish fishery. 



It is indeed unfortunate that the statistical data on the commercial fishery for 

 whitefish are less satisfactory than those for any other important commercial species. 

 The invention and rapid expansion in the use of that tremendously efficient gear, the 

 deep trap net, brought about, particularly in Lake Huron, an almost immediate threat 

 of depletion or commercial extinction to the whitefish stocks of the areas in which the 

 net was fished. In this critical situation the need for dependable statistical measures 

 of abundance was most pressing. However, the very circumstances that made the need 

 for adequate statistical data so urgent also made the interpretation of these data difficult. 

 The chief obstacles to appraising the statistical data on the whitefish over the period, 

 1929-1939, are: lack of information concerning normal conditions, inaccurate data on 

 the deep-trap-net fishery, and the difficulty of bridging the transition to a fishery domi- 

 nated by this gear. 



As stated earlier (p. 314), in the statistical study of the important commercial 

 species in the State of Michigan waters of the Great Lakes, the average conditions of 

 production, abundance, and fishing intensity during the 6-year period, 1929-1934, were 

 employed tentatively as the point of reference for the study of fluctuations. The 

 fisheries for most species appeared to be approximately normal (with reference to 

 modern conditions) during this period; consequently the fi-year averages may be ex- 

 ported to provide a fairly reliable basis for estimating changes in the condition of the 

 fisheries, not only in that period but in subsequent years as well. 



The whitefish fishery, however, was not normal in the years, 1929-1934, nor can 

 the average conditions in the longer period, 1929-1939, be held to provide a satisfactory 

 point of reference. It is recognized generally that whitefish were abnormally abundant 

 at the beginning of these periods. The peak of abundance probably was reached in 

 Lake Michigan in 1929 and in Lake Huron a year or so later. The high abundance in 

 turn stimulated fishing intensity. As a result, production, abundance, and fishing in- 

 tensity were all doubtless far above normal in the earlier years of the period for which 

 detailed statistics are available. It should then be kept in mind throughout the discus- 

 sion of the following sections that all fluctuations are described with reference to aver- 

 ages the relationship of which to the normal is not known. 



The interpretation of the Lake Huron data is made even more difficult by the 

 disturbing effects of the use of the deep trap net. This gear, which became the domi- 

 nant one for the capture of whitefish as early as 1931, raised production to excessive 

 heights and disrupted completely the ordinary course of return to normal conditions. 



