DECLINE OF THE LAKE TROUT FISHERY IN LAKE MICHIGAN 



By Ralph Hile and Paul H. Eschmeyer, Fishery Research Biologists, and George F. Lunger, Statistician 



Collapse of the fishery for lake trout, Salveliniis 

 [=Cristivomer] namaycush, of Lake Huron has 

 been treated in detail in a recent publication by 

 Hile (1949). In the present paper we take up the 

 unpleasant task of describing the decline of the 

 lake-trout fishery in yet another of the Great 

 Lakes, Lake Michigan. Lake Superior now stands 

 as the only significant center of conunercial pro- 

 duction of that species yet remaining in the United 

 States. 



In this, as in the earher paper mentioned, treat- 

 ment will be limited to a statistical account of the 

 changes that have taken place in the lake-trout 

 fisheiy. We offer no extended argument on the 

 role of the sea lamprey in this most recent debacle, 

 other than to express the considered opinion that 

 on the basis of ciu-rently available evidence this 

 parasite must be held the major cause of the 

 catastrophes that have overtaken both Lake 

 Huron and Lake Michigan. 



MATERIALS AND METHODS 



The statistics on the production of lake trout 

 in the individual States over the period 1879- 

 1940, incorporated in table 1, were adapted from 

 Gallagher and Van Oosten (1943) and are from 

 the sources listed in that publication. Our annual 

 totals, however, are in agreement with those of 

 Gallagher and Van Oosten only for those years in 

 which statistics were available for aU four States 

 bordering the lake. In a number of years statis- 

 tics were at hand for Michigan and Wisconsin but 

 not for lUmois and Indiana; in such situations 

 those authors recorded the yields from the first 

 two States as the totals for Lake Michigan. Our 

 totals in the same situations include estimates of 

 the Illinois-Indiana catch. On the basis of the 

 actual distribution of the take among the States 

 in the 8 years with complete data from 1885 

 through 1917 and in the 6 years ' from 1922 



' For this purpose the 1925 data were usable since the Indiana-Illinois 

 catch was included in the total; statistics for the two States Individually, 

 however, were not available. 



through 1929 we derived the correction factors 

 1.0291 and 1.0683. The former factor was ap- 

 plied to the combined Michigan-Wisconsin catch 

 to give an adjusted grand total in years lacking 

 lUinois-Indiana data through 1919; the latter 

 factor was used for years after 1919. To be sure, 

 the percentage contribution of Illinois and Indiana 

 varied within each of the two periods, but the 

 derivation of a greater munber of factors would 

 not have been profitable. We have not consid- 

 ered it advisable to estimate the Lake Michigan 

 total in any year for which we had data for only 

 one State. 



Statistics on production after 1940 were com- 

 piled directly from commercial fishei-men's re- 

 ports in the Ann Arbor offices of the Fish and 

 Wildlife Service (Michigan) or supplied by State 

 conservation agencies (Wisconsin, Illinois, and 

 Indiana) . 



The data on the yield of lake trout in the several 

 statistical districts of the State of Michigan waters 

 of Lake Michigan for 1891-1908 were tabulated in 

 the Service's Great Lakes offices from original 

 records supplied by the Michigan Department of 

 Conservation." 



The detailed information on production, fishing 

 intensity, and estimated availability of lake trout 

 in the State of Michigan waters in 1929^9 is 

 based on analyses of monthly reports of com- 

 mercial fishermen licensed by the State of Michi- 

 gan. These reports, which were supplied by the 

 department of conservation, contain data on 

 fishing locality, kind and amount of gear fished, 

 and kinds and quantities of fish captured for each 

 day of fishing by each Ucensee. 



The methods employed in estimating the 

 abundance of the principal species and the intens- 

 ity of the fishery in the State of Miciiigan waters 

 of the Great Lakes have been described in detail in 

 earlier publications (Hile 1937; Hile and Jobes 



> The Works Progress Administration gave valuable assistance in this 

 vorlc 



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