90 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



unit of fishing effort together with the very fact 

 that production had all but ended in most areas 

 must be accepted as conclusive evidence of the 

 great scarcity of marketable-sized lake trout in 

 the State of Michigan waters of Lake Michigan in 

 1949. 



For the combined districts the level of abun- 

 dance was highest in 1943 (126), 1941, and 1942. 

 The last year with abundance above average and 

 the first year of the recent progressive decline 

 was 1944, and abundance first dropped below the 

 70-percent level in 1947. In 1949 the abundance 

 had reached the low figure of 26 percent. 



Table 13. — Correlations between 1929-43 fluctuations in 

 abundance indices for lake trout in Michigan statistical 

 districts 



[Values of r corresponding to probabilities p of 0.05 and 0.01 are ±0.514 and 

 ±0.641] 



From earlier discussion and from the examina- 

 tion of table 9 and figures 3, 4, and 5, it is apparent 

 that in certain districts the annual fluctuations in 

 the abundance of lake trout followed similar 

 trends. In the northern waters for example, it 

 has been pointed out that most of the years of 

 highest abundance fell before 1940, whereas the 

 southern districts shared a period of high avail- 

 ability in the early 1940's. To provide a more 

 precise measurement of the agreement in these 

 trends, coefficients of correlation were computed 

 for the abundance percentages for aU pairs of 

 districts over the period 1929-43. Data for 

 yeare later than 1943 were excluded in order to 

 minimize or possibly eliminate the distorting 

 effects of the decline in abundance that followed 

 the depredations of the sea lamprey in all districts. 

 This restriction, we believe, has made the coeffi- 

 cients recorded in table 13 relatively reliable 

 estimates of the correlations between fluctuations 

 in the availability of lake trout in the difl'erent 

 districts under approximately "normal" condi- 

 tions. 



The outstanding feature of the data of table 

 13 is the close positive correlation among the 

 fluctuations in abundance in the four southern 

 districts (M-5 thi-ough M-8). Of the sLx coeffi- 

 cients that could be computed for these districts, 

 five exceeded the value ordinarily accepted as 

 "higlily significant" (p<^0.01), and the sixth was 

 above the level ordinarily termed "significant" 

 (^<0.05). These high values, together with the 

 consistency with which they occurred with all 

 possible pairings, suggest strongly that the lake- 

 trout fisheries to the south of Grand Traverse 

 Point were based on a common stock or on stocks 

 in which the factors controlling abundance in 

 1929-43 were the same or subject to sunilar 

 annual fluctuations. Further speculation in the 

 matter would be to little point until we have 

 definite information on the nature of these factors 

 and the methods by which they operate. 



The fluctuations of abundance in M-4 exhibited 

 positive significant correlation with those in the 

 two districts immediately to the south (M-5 

 and M-6). The correlation with fluctuations in 

 M-3 also was positive but the value of the coeffi- 

 cient (r= 0.404) was well below the level of 

 significance. 



Of the 3 coefficients computed between districts 

 M-1, M-2, and M-3, and the 15 calculated 

 between those districts and the ones lying farther 

 south, only one was significant (r= — 0.617, M-2 

 and M-8). This single significant value in a 

 group of 18 faUs to fit the pattern. The weight 

 of the evidence suggests that the fluctuations in 

 the abundance of lake trout in each of the three 

 northern districts were not correlated with those 

 ia the remaining ones. 



FISHING INTENSITY IN STATE OF 

 MICHIGAN WATERS, 1929-49 



The records of the annual fluctuations in the 

 intensity of the fishery for lake trout (table 14; 

 figs. 3, 4, and 5; bottom section of table 8) fail 

 to reveal the distmct separation with respect to 

 trends that existed between northern and southern 

 areas in production and abundance. With the 

 exception of M-2 where all three years and M-8 

 where two of the three years of most intensive 

 fishing occurred in the 1940's, the tendency was 

 general for fishmg operations to be heaviest in the 

 early 1930's. Of the 21 "high-intensity" years 

 listed in table 8 (see section on production in the 



