80 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 2. — Average production of lake trout in Lake Michigan, by periods 

 [In thousands of pounds] 



Period 



Number 

 of years ' 



Item 



State 



Michigan Wisconsin Illinois Indiana 



Total 



1879 



1885-89.. 



1890-1911 



1912-26 



1927-39 



1940-44 



1946-49 



Production- 

 Mean annual 



Percentage 

 Mean annual 



Percentage 

 Mean annual 



Percentage 

 Mean annual 



Percentage 

 Mean annual 



Percentage 

 Mean annual 



Percentage 



production.. 



of total 



production. 



of total 



production. 



of total 



production. 



of total 



production. 



of total 



production, 

 of total 



3,338 



55.6 

 3,492 



42.4 

 3,033 



43.3 

 2.417 



45.7 

 2,807 



42.7 

 1.172 



43.8 



2,562 



42.7 



!4.512 



54.8 



' 3, 580 



61.1 



' 2, 473 



46.7 



2, 722 



41.4 



1,200 



44.9 



14 

 2 

 143 

 1.8 

 179 

 2.6 

 269 

 4.9 

 972 



14.7 

 302 



11.3 



92 

 1.5 



83 

 1.0 

 215 

 3.1 

 144 

 2.7 



78 



1.2 











2,659 

 6,n06 



100 

 8,230 



100 

 7,007 



100 

 6,293 



100 

 6,578 



100 

 2,674 



100 



1 Number of years for which statistics were available in at least 1 State or 

 for the entire lake. 



2 The reported Wisconsin production for the years 1892 and 1899 was far 

 below the level characteristic of the period. If these years are excluded, the 

 Wisconsin mean becomes 4,822 and the percentages and total change 

 accordingly. 



pounds in Illinois, a rise exceeding the combined 

 increases in Michigan (390,000 pounds) and Wis- 

 consin (249,000 pounds). Indiana alone experi- 

 enced a decline (66,000 pounds). 



The sharp drop in the recorded Indiana take to 

 a lower level during the 1940-44 interval probably 

 reflects improvement in the collection of statistics 

 more than a decrease in output. Indiana pro- 

 ducers, who traditionaUy take the bulk of their 

 catch of lake trout in State of Michigan waters, 

 have to our best knowledge customarily reported 

 their entire production to both Indiana and Mich- 

 igan. There is considerable evidence, therefore, 

 that part of the take of Indiana fishermen in 

 earlier years was reported in duplicate. In view 

 of the relatively small production of these opera- 

 tors, the efl^ects on the statistics for the entire lake 

 were not particularly damaging, but the figures for 

 Indiana before about 1942 must be viewed with 

 some skepticism. 



The period 1940-44 is exceptional for its brevity. 

 Statistics for the preceding three periods demon- 

 strated a tendency for the productivity of the lake- 

 trout fishery to fluctuate closely about a character- 

 istic level for from 13 to 22 years. In view of this 

 tendency, it might well be expected that the new 

 high level reached in 1940 would be maintained 

 longer than 5 years. That it was not maintained 

 suggests that some disruptive factor intervened. 

 The sea lamprey qualifies well as that factor. 



Although the downward trend of production 



' Excluding 1921 for which year the reliability of the Wisconsin data appears 

 questionable. 



* The reported Wisconsin production for 1929 was considerably above the 

 level characteristic of the period. If this year is excluded, the_ Wisconsin 

 mean becomes 2,362 and the percentages and total change accordingly. 



actually started a year earlier, 1945 can be set a 

 the beginning year of the recent disastrous decline. 

 In this year the catch dropped by more than a 

 million pounds and fell distinctly below the level 

 of 1940—44. Once the decline started, its progress 

 was spectacular. In 1946 the take was under 4 

 million pounds for the first time since 1879, and 

 each of the years 1947 to 1949 set a new record 

 low. It is the high rate of decrease rather than 

 the average of 2,674,000 pounds that makes the 

 1945-49 period significant. 



The collapse of production in the lake-trout 

 fishery of Lake Michigan resembles closely that 

 described for Lake Huron by Hile (1949). Indeed, 

 the decline appears to have been even more rapid 

 in Lake Michigan than in the United States 

 waters of Lake Huron. This point can be brought 

 out by a comparison of the number of years 

 required for a 90-percent or gi-eater decline from 

 the last year with the take above the "modern" 

 average. In Lake Michigan this average can 

 be set at 5,651,000 pounds (the mean for 1927-44), 

 and the last year in which the take exceeded that 

 figure was 1944 (6,498,000 pounds); only 5 years 

 later the catch had dropped by 94.7 percent 

 (to 342,000 pounds m 1949). In the United 

 States waters of Lake Huron the "modern normal 

 yield" was set by Hile at 1,685,000 pounds (the 

 mean for 1895-1939), and the last year with an 

 output above this figure was 1935 (1,743,000 

 pounds); 10 years were required for the catch 

 to decline 90.1 percent (to 173,000 pounds in 1945). 



