DECLINE OF LAKE TROUT IN LAKE MICHIGAN 



95 



dance at or above the 1929^3 index of 100 and 

 on the first year of abundance below 70 (a level 

 of availability selected as critical in this study) 

 give strong indication of a north-to-south pro- 

 gression in the timing of the recent decline (wTth 

 the more northerly districts the first to drop below 

 average and to pass the 70-percent level). This 

 sequence suggests that the different areas may 

 have been affected successively as the sea lamprey 

 spread from the north to the south. Despite this 

 progression, all eight districts agreed in exlii biting 

 an extremely low level of abundance in 1949 (from 

 12 to 45 percent of average in the individual 

 districts; 26 percent for the combined districts). 



During the more nearly normal years preceding 

 the recent general decline of the lake-trout fishery, 

 the annual fluctuations in the abundance of lake 

 trout in the four southern districts (M-5 through 

 M-8) were closely correlated. The coefficient of 

 correlation r was highly significant (p<C0.01) for 

 five of six possible pairings over the period 1929-43 

 and was significant (p<0.05) for the sixth. The 

 fluctuations of abundance in M-4 also were coiTe- 

 lated significantly with those in M-5 and M-6. 

 The abimdance in each of the northern districts, 

 on the contraiy, appeared to be independent of 

 that in any other area. 



In the majority of the statistical districts the 

 years of most intensive fishing for lake trout fell 

 in the early 1930's and for the combined districts 

 the three years of greatest fishing intensity were 

 1930, 1931, and 1932. With the exception of M-1, 

 where a recent upswing in the intensity of fishing 

 for whitefish led to an increased pressiu-e on lake 

 trout, fishing intensity for the latter species en- 

 tered on a progressive decline as early as 1942 and 

 in no district later than 1947. By 1949, fishing 

 intensity was far below 50 percent of the 1929^3 

 average in aU districts but M-1 and amoimted to 

 only 26.5 percent for the eight districts combined. 

 The abundance of lake trout seems to have had 

 little influence on the intensity of the fishery under 

 the nomial conditions of 1929-41 (before World 

 War II with its shortages of manpower and equip- 

 ment and well before the general decline of the 

 lake-trout fishery associated with the spread of 

 the sea lamprey) . 



Dming the same normal 1929^1 period, fluc- 

 tuations in production served as reasonably de- 

 pendable indicators of major changes in abundance 

 in five of the eight districts. These changes in 



production did not, however, provide rehable 

 measures of the extent of the fluctuations in 

 abundance. 



Statistics on the production and abundance of 

 lake ti'out and on the intensity of the lake-trout 

 fishery refute the view sometimes advanced that 

 overfishing has been the cause of the decline of 

 the lake trout in the State of Alicliigan waters of 

 Lake Michigan. The most intensive fishing of 

 the 1929-49 period took place in 1930-32, and 

 intensity has been consistently below the 1929-43 

 average since 1941. Some factor other than over- 

 fisliing caused the lake trout to disappear. The 

 best evidence points to the sea lamprey. 



LITERATURE CITED 



Do.\N, Kenneth H. 



1942. Some meteorological and limnological 

 conditions as factors in the abundance of 

 certain fishes in Lake Erie. Ecol. Mon., 

 vol. 12, pp. 293-314. 



Gallagher, Hubert R., and John Van Oosten. 



1943. Supplemental report of the United 

 States members of the International Board 

 of Inquiry for the Great Lakes Fisheries. 

 International Board of Inquiry for the 

 Great Lakes Fisheries — Report and Sup- 

 plement, pp. 25-213. 



HiLE, Ralph. 



1937. The increase in the abundance of the 

 yeUow pike-perch, Stizostedion vitreum (Mit- 

 chill), in Lakes Huron and Michigan, in 

 relation to the artificial propagation of the 

 species. Trans. Amer. Fish. Soc, vol. 

 66 (1936), pp. 143-159. 



1949. Trends in the lake trout fishery of 

 Lake Huron through 1946. Trans. Amer. 

 Fish. Soc, vol. 76 (1946), pp. 121-147. 

 Hile, Ralph, and Frank W. Jobes. 



1941. Age, growth, and production of the 



yeUow perch, Perca flavescens (Mitchill), 



of Saginaw Bay. Trans. Amer. Fish. Soc, 



vol. 70 (1940), pp. 102-122. 



Van Oosten, John, Ralph Hile, and Frank W. 



Jobes. 



1946. The whitefish fishery of Lakes Huron 

 and Michigan with special reference to the 

 deep-trap-nct fisheiy. Fisheiy Bull., U. S. 

 Fish and Wildlife Service, vol. 50, pp. 

 295-394. 



O 



