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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



tion, but the lack of a simOar correlation in the 

 other districts throws some doubt on such an 

 interpretation. 



The general situation in the State of Michigan 

 waters seems to be much the same as that in the 

 United States waters of Lake Huron where Hile 

 (1949) concluded that "indispensable as the lake 

 trout may be to the conduct of a lake trout 

 fisheiy, the abundance of that species is only one 

 of the factors, and in some situations a subordinate 

 factor, in the determination of fishing intensity." 



RELATIONS OF PRODUCTION, 

 ABUNDANCE, AND FISHING INTENSITY 



Considerable infoi-mation on the relations of 

 production, abundance, and fishing intensity in 

 the lake-trout fishery of the State of Michigan 

 waters of Lake Michigan was given in the preced- 

 ing sections. The discussion of the present sec- 

 tion is restricted largely to the question of the ex- 

 tent to which production has served as an indica- 

 tor of fluctuations in the abundance of lake trout 

 and to changes in the fishery immediately pre- 

 ceding and dm-ing the recent collapse, with special 

 reference to the possible role of overfishing as a 

 factor in the decline in abmidance of lake trout. 



The accumulation of information on the degree 

 of reliability of production statistics as indicators 

 of changes in abundance or availability in the 

 Great Lakes fisheries is of importance because in 

 many areas data on the actual take per unit of 

 fishing effort are not available or are at hand for 

 only the more recent years. 



The opinion was expressed by Van Oosten, HUe, 

 and Jobes (1946) that "imder normal conditions 

 (without disruption in the methods or regulations 

 of the fishery), over limited areas, and for short 

 periods of years, large increases or decreases of 

 production may serve as reliable indicators of in- 

 creases or decreases in the abundance of fish on 

 the grounds." A similar view was held by Doan 

 (1942) who considered it valid to employ catch 

 statistics for the estimation of the fluctuation in 

 the abundance of several commercially important 

 species in Lake Erie. Doan based his opinion 

 largely on the agreement between trends in the 

 catch of walleyes or yellow pikeperch {Stizostedion 

 V. vitreum) per unit effort in the principal gear and 

 the total production of the species in four fishing 

 areas of Lakes Huron and Michigan (data for these 



two lakes adapted from Hile 1937) and in Lake 

 Erie. More recently, Hile (1949) demonstrated a 

 significant positive correlation between annual 

 fluctuations in the production and abundance of 

 lake trout for four of the sLx statistical districts of 

 the United States waters of Lake Huron and for 

 the six districts combined. In a fifth area the co- 

 efhcient was positive with a value corresponding 

 to the 10-percent level of probabihty, but a sig- 

 nificant negative value existed in the sixth district. 

 This negative correlation was explained as the 

 result of the depressing effect of the collapse of the 

 whitefish fishery on the intensity of operations with 

 large-mesh gill nets dui'ing years of relatively high 

 abundance of lake trout (note the similar situation 

 described earlier in this paper for district M-1). 



Of the coefficients of correlation between the 

 production and abimdance computed for Lake 

 Michigan (table 15) those for the period 1929-41 

 most nearly reflect "normal" conditions. The co- 

 efficients for the base period 1929-43 were prob- 

 ably biased by the depressing effects of wartime 

 scarcities of manpower and equipment and those 

 for 1929—49 were affected by wartime conditions 

 and more recently by the general collapse of the 

 lake-trout fishery. 



Table 15. — Correlations between production and abundance 

 of lake trout in Michigan statistical districts, for 3 periods 



Actually, the differences between 1929-41 and 

 1929-43 were unimportant. In both periods the 

 correlations between production and abimdance 

 were "highly significant" (p<0.01) for M-6, M-7, 

 and M-8 and were "significant" (0.05>p>0.01) 

 for M-2 and M-5 and for the combined districts. 

 The positive coefficients for M-3 were moderately 

 high but nevertheless fell short even of the 10-per- 

 cent value in 1929-41 and barely attained that 

 level in 1929-^3. The 1929-41 and 1929^3 data 



