I 



DECLINE OF LAKE TROUT IN LAKE MICHIGAN 



91 



Table 14.- 



-Intensity of fishery for lake trout in Michigan 

 statistical districts, 1929-49 



various districts for an account of the unusual 

 situation ia M-1) 12 fell within the 4-year period 

 1930-33. 



The last year of average or greater fishing 

 intensity was 1939 in M-5, 1941 in M-6, and 1944 

 to 1946 in the remaining districts. The recent 

 progressive decline started in 1942 in M-6 and in 

 1944 to 1947 in other areas. Fishing intensity 

 first dropped below the 50-percent level in 1947 

 m M-2, M-5, and M-6, in 1948 in M-3, M^, and 

 M-7, and m 1949 in M-8. 



For the combined districts the intensity of the 

 lake-trout fishery was greatest in 1930, 1931, and 

 1932, and the last year of greater-than-average 

 intensity was 1941. The recent progressive de- 

 cline started in 1947, and in 1949 fishing intensity 

 was only 26 percent of the 1929-43 mean. 



The factors that influence the intensity of the 

 fishery for lake trout are so numerous, so variable 

 in their effects, and so difficult to appraise, that in 

 most situations it is impossible to evaluate the 

 effect of any one of them. Among these factors 

 may be listed: Weather conditions; costs of 

 operation; availability of and market for lake 

 trout, for species taken along with lake trout, and 

 for species produced alternatively. During the 

 war years scarcities of equipment and supplies 

 and manpower shortages also affected fishing 

 intensity. 



The availability of the lake trout itself well 

 might be expected to exert an important influence 



on the intensity of fishing since good catches per 

 unit of effort shoidd stimulate fishing operations 

 and poor lifts depress them. This expectation 

 is not borne out, however, by the following 

 tabulation of the coefficients of correlation between 

 the abundance of lake trout and fishing intensity 

 for the species in the various districts in 1929^1 :"" 



r 



District M-1 -0. 611 



District M-2 .034 



District M-3 -. 378 



District M-4 -. 677 



r 



District M-5 -0. 379 



District M-6 . 225 



District M-7 .357 



District M-8 . 633 



Of the eight coefficients calculated, four were 

 positive and four negative, and of the three that 

 were "significant" (r= ±0.553 at the 5-percent 

 level of probability) one was positive and two 

 negative. It is not to be concluded, of course, 

 that a plenitude of lake trout is about equaUy 

 likely to stimulate or depress fishing activity; 

 rather, it should be stated that in many situations 

 other factors are of greater importance. 



The high negative correlation between fishing 

 intensity and abundance of lake trout in M-1 

 has already been explained. The available sta- 

 tistical data do not suggest an explanation of the 

 even higher negative figure for M-4. Perhaps 

 this significant correlation was merely fortuitous. 

 We are inclined to suspect, however, that the neg- 

 ative correlation can be attributed in part to 

 changes of fishing grounds during the time of the 

 great increase in the popularity of "deep-sea' 

 troUing for lake trout in Grand Traverse Bay 

 (identical with M^) in the 1930's. Although we 

 have no quantitative measure of the effect on the 

 intensity of the fishery, we do know that certain 

 fishermen, in an attempt to lessen friction between 

 sport and commercial interests, avoided the sport- 

 trolling grounds during the peak of the tourist 

 season and moved their operations to grounds 

 north of Grand Traverse Point (M-3) and near 

 Cathead Point (M-5). Consequently, fishing in- 

 tensity may have been lower than normafly would 

 be expected in some years when lake trout were 

 relatively plentiful. 



The significant positive correlation between 

 fishing intensity and the abundance of lake trout 

 in M-8 may reflect a true cause-and-effect rela- 



'0 The elimination of years after 1911 in these computations makes possible 

 the best estimate of rel.itions under approximately "normal" conditions since 

 bias from wartime shortages of manpower and materials and the effects of the 

 general sharp deline in abundance that accompanied the increase in the 

 population of sea lampreys in recent years are eliminated or minimized. 



