94 



FISHERY BtTLLETESr OF THE FISH AND WILDLIFE SERVICE 



Table 16. — Indices of production, abundance, and fishing 

 intensity for lake trout in Slate of Michigan waters, 1929-49 



[Percentages of 1929-43 means] 



been invariably below the 100-percent value since 

 1941. It is particularly significant that intensity 

 was below average in 3 of the 4 years of highest 

 abundance (1941-44) and was barely above the 

 15-year mean in the fourth. These same years 

 saw production consistently above the mean and 

 at a 21 -year peak in 1941, but a high level of 

 abundance, not intensive fishing, was the cause. 

 Furthermore, the intensity percentage exceeded 

 the abundance percentage in only 2 of the 9 years 

 of the period 1941-49; in the remaining 7 years 

 the two index figures were the same or fishing in- 

 tensity was the lower. It is thus obvious that a 

 rate of fishing that could bring the index of 

 abimdance from a record high figure of 126 in 



1943 to a record low value of 26 in 1949 simply 

 did not exist. Some factor other than overfishing 

 caused the lake trout to disappear in Lakes Huron 

 and Michigan. The best evidence points to the 



sea lamprey. 



SUMMARY 



After a developmental period from 1879 through 

 1889, the fishery for lake trout, Salvelinus [=Cris- 

 tivomer] namaycush, in Lake Michigan entered on 

 a 22-year period (1890-1911) of high and rela- 

 tively stable production. The average annual 

 output for this latter interval was 8,230,000 

 pounds. There followed two shorter intervals of 

 15 years (1912-26) and 13 years (1927-39) in 

 which the annual yields were still moderately 

 stable but had successively lower average values 

 of 7,007,000 and 5,293,000 pounds. Production 

 rose in 1940 but the heightened prosperity was 

 short-lived. After 5 years (1940-44) in which the 

 yield was consistently more than 6 million pounds 

 and averaged 6,578,000 pounds, the lake-trout 

 fishery suffered a calamitous decline which saw 

 the annual catch drop from 6,498,000 pounds in 



1944 to only 342,000 pounds in 1949. 



Michigan and Wisconsin have always contrib- 

 uted the bulk of the production of lake trout in 

 Lake Michigan. The contribution of Michigan 

 for the periods listed in the preceding paragraph 

 (excluding the developmental years for which only 

 scattered data were available) ranged from 42.4 

 percent in 1890-1911 to 45.7 percent in 1927-39. 

 In Wisconsin the range was from 41.4 percent in 

 1940-44 to 54.8 percent in 1890-1911. The per- 

 centages have been consistently small for Indiana 

 (maximimi of 3.1 percent in 1912-26) and were 

 smaU for Illinois also in the earlier years. More 

 recently Illinois contributed 14.7 percent of the 

 total for the lake in 1940-44 and 11.3 percent in 

 1945^9. 



Comparison of the aimual yields of lake trout 

 in the eight statistical districts of the State of 

 Michigan waters of Lake Michigan in 1891-1908 

 with those of 1929-43 (the base period for our 

 modern statistical analyses) revealed a lower 

 level of productivity in more recent years for 

 every district but M-5 and a slight southward 

 shifting of the centers of production (the north- 

 erly districts M-1 through M-3 contributed 

 60.3 percent of the 1891-1908 total but only 

 49.1 percent of the 1929-43 yield). The ranking 

 of the districts with respect to their percentage 

 contribution to the lake total changed little, 

 however. 



Production statistics for the individual dis- 

 tricts in 1929-49 showed that most of the years 

 of relatively high production (the three best 

 years for each district) fell before 1940 in north- 

 erly waters (M-1 through M-3) and after 1940 

 in southerly waters (M-4 through M-8). Al- 

 though the recent progressive decline in produc- 

 tion got under way earlier than 1944 in only one 

 district and started as late as 1947 in M-7 and 

 M-8, the catch had dropped to an insignificantly 

 low level in all districts by 1949 (an exception 

 must be made for M-1 where considerable quan- 

 tities of lake trout were taken coincid en tally in 

 an abnormally intensive fishery for whitefish). 



Records of the three years of greatest abun- 

 dance or availability of lake trout (as computed 

 from the data on the catch per unit of fishing 

 eft'ort of the principal gears) revealed that most of 

 these years fell before 1940 in districts M-1 

 through M-4, whereas in the waters to the south 

 (M-5 through M-8) they all fell within the period 

 1940^4. Figures on the last year with abun- 



