WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 333 



the curve of total production in 1931 if only gill nets and pound nets had been in opera- 

 tion. The deep-trap-net catch, however, changed the form of the curve completely. 

 This gear not only deprived the whitefish of its former temporary respite during the 

 period of habitation in deep waters, but actually exposed the fish to a far more severe 

 exploitation in late summer than it had previously suffered at any season. From these 

 facts it is obvious that effective regulation of the deep trap net must include the reduc- 

 tion of its catches on the deep-water grounds on which whitefish congregate during late 

 summer. 



The summer assemblings of whitefish that made possible the great effectiveness of 

 the deep trap net seemingly were not as dense in northern Lake Huron as in the central 

 and southern regions of the lake. In each of the four southerly districts the average 

 catch per lift of deep trap nets exceeded 4U0 pounds in one year and was more than 

 200 pounds per lift in 2 or 3 years (table 111. In the northern districts the greatest 

 average catch per lift of deep trap nets was 168 pounds in H-l and 142 pounds per lift 

 in H-2 (in 1930 in both districts). The relatively poor success of deep trap nets is the 

 more remarkable in H-l because that area under normal conditions had been an im- 

 portant and in many, if not the majority of years, the leading center of whitefish 

 production in the lake. At any rate these small catches per lift account for the more 

 moderate use of deep trap nets in H-l and H-2. 



A final point that deserves consideration is the possibility that mass migrations of 

 whitefish may have played a role in the shift from year to year in the center of the 

 deep-trap-net fishery. The failure of the grounds on which the deep trap nets first were 

 fished and the resultant necessity for opening up new areas gave an early indication of 

 the disastrous results to be expected from the unrestricted operation of this gear. 

 Deep-trap-net fishermen denied most vigorously, however, that their activity had caused 

 any depletion on the grounds. They contended that the fish had not been caught but 

 that they merely had migrated to another area. They held further that in changing the 

 center of the fishery they were only following the movements of the whitefish popula- 

 tion. In support of their contention they stressed the argument that only mass migra- 

 tions could make possible such high production in southern Lake Huron (H-5 and H-6) , 

 an area in which the catch of whitefish hadalways been small. 



The assumption of a mass migration of whitefish proceeding in the same direction 

 year after year runs counter to all known facts concerning the habits of the species. 

 Nevertheless, the possibility cannot be denied that extraordinary conditions might bring 

 about unusual reactions on the part of the fish. The strongest argument against the 

 theory of mass migration lies in the fact that such an assumption is altogether unne- 

 cessary. The heavy yield in southern Lake Huron in 1932 and later years was not 

 made possible, as fishermen contended, by the influx of whitefish from more northerly 

 grounds. The records of the catch of gill nets per unit of effort (table 11) prove that 

 dense concentrations of whitefish had been present on the offshore grounds of H-5 and 

 H-6 for years before the deep trap net was introduced. In fact, the catch of whitefish 

 per unit of effort of gill nets in H-5 exceeded that in every other district during the 

 four years, 1929-1932. The catch per unit of effort of gill nets in H-6 was greater than 

 that in anv other district in 1933 and was second onlv to the catch per lift in H-5 in 

 1931 and 1932. 



The large production of deep trap nets in H-5 and H-6 was made at the expense 

 of the reserve stock rather than of a population of recent migrants. The generally low 

 output of whitefish in southern Lake Huron prior to the introduction of the deep trap net 

 can be attributed to a low fishing intensity. Gill nets, comparatively ineffective gear 

 for the capture of whitefish, accounted for the bulk of the catch (appendix B). Appar- 

 ently the relatively few pound nets were fished either at the wrong localities or depths to 

 produce large quantities of whitefish. Actually, suitable localities for whitefish pound 

 nets are scarce in southern Lake Huron. 



WHITEFISH FISHERY OF LAKE MICHIGAN, 1929-1939 



The most important difference between the histories of the whitefish fisheries of Lakes 

 Michigan and Huron, 1929-1939, lies in the relatively limited development of the deep- 



