84 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 7.- — Correlations between abundance and fishing- 

 intensity indices for lake trout and whitefish in district 

 M-1 



' Data given for two earlier periods as well as for entire 21 years since war- 

 time conditions disrupted normal trends in fishing intensity after 1941 and 

 the extremely low abundance of lake trout introduced a disturbing factor 

 after 1943. 



were an important factor in deteimining the rate 

 of fishing; the correlation that did exist is negative 

 (table 7). It should be emphasized here that the 

 estimate of fishing intensity for a particular 

 species is based only on gear lifted on days when 

 some quantity of that species was captured. Third, 

 the fluctuations in fishing intensity for lake trout 

 followed closely those of the gUl-net fishery for 

 whitefish (most lake trout are captured in gill nets), 

 and fishing intensity for whitefish in turn was 

 correlated closely with the fluctuations in the 

 abundance of that species. The data of tables 6 

 and 7 thus offer rather conclusive evidence that 



the availability of whitefish is of primary signifi- 

 cance in the determination of the intensity of the 

 lake-trout fishery. 



The situation just described for district M-1 is 

 not entirely without paraUel. Hile (1949) demon- 

 strated that in three districts of Lake Huron in 

 which lake trout and whitefish ordinarily were 

 taken together in a "two-species fishery" (catches 

 of other varieties in this type of fishery are usually 

 imimportani) the fluctuations in the availability 

 of whitefish exerted a readily detectable effect on 

 the fishing intensity for lake trout. The condi- 

 tions in M-1 merely represent an extreme because 

 of the strongly predominant position of whitefish 

 in the joint fishery and also because of the tre- 

 mendous upturn in the abundance of whitefish and 

 hence in fishing intensity for both whitefish and 

 lake trout at a time when the availability of the 

 latter species was far below normal. 



Comments on the 1929-49 trends of production 

 in the several statistical districts as recorded in 

 table 4 will be based largely on the summary in 

 the top section of table 8. Reference to the pro- 

 duction curves of figures 3, 4, and 5 also should 

 prove helpful. 



A pronounced difference is to be detected be- 

 tween the "northern" districts (M-1, M-2, M-3) 

 and the remaining or "southern" districts with 

 respect to the calendar years of highest produc- 

 tion of lake trout within the period 1929-49. Of 



Table 8. — Summary of -production, abundance, and fishing intensity for lake trout in Michigan statistical districts, 1929-49 



' 1948 and 1949 production above average. 

 2 Decline interrupted by increases in 1947 and 1948. 

 ' First recent year; production less than half average in 1934 and 1942. 

 < First recent year; production less than half average in 1936. 

 ' Decline interrupted by increases in 1948 (followed by further slight rise 

 In 1949 in M-1). 



• First recent year; abundance below 70-percent level in 1930 and/or 1931. 



' Fishing intensity so closely linked with availability of whitefish that 

 summary would be meaningless and possibly misleading; see p. 83. 



• 1941 if irregularities in 1944 and 1946 are ignored. 



• Intensity unquestionably would have been less than 50 percent of average 

 In 1948 but for the abnormal situation in M-1; see p. 83. 



