88 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Despite the differences between the northern 

 and southern waters just outlined, all districts 

 agreed in showing production equal to or greater 

 than the 1929^3 mean in relatively recent years. 

 If we ignore the 1948-49 data for M-1, where, as 

 explained, conditions were abnormal, the situation 

 can be described by the statement that every 

 district had average or better production in 1942 

 or later and in two districts (M-7 and M-8) the 

 take was still above the mean in 1946. 



The districts agreed further in that the onset 

 of the progressive decline which has caused so 

 much concern and the drop of production to less 

 than half the average also were recent. In only 

 one of the eight districts (M-6) did the recent 

 progressive decrease get imder way before 1944, 

 and in the southernmost waters (M-7 and M-8) it 

 did not start until 1947. With the exception of 

 M-1 and M-2 (again 1948-49 data are ignored in 

 the former district) the 50-percent level was not 

 passed before 1947, and in M-7 and M-8 the 

 take did not drop below half the mean untU 1948. 

 These data suggest a distinct north-to-south 

 trend in the time at which the decline set in. 



Despite the lateness of the decline, the speed 

 with which it progressed was such that by 1949 

 the lake-trout fishery had practically come to an 

 end in all districts but M-1. The 1949 total catch 

 for districts M-2 through M-8 was only 74,000 

 pounds. These same waters had yielded more 

 than 3 million pounds as recently as 1941 and in 

 excess of 2 million pounds as late as 1945. The 

 decline since the latter year represents a decrease 

 of 96.7 percent. 



The production data for the combined districts 

 may be summarized as follows: Highest yields 

 occurred in the early 1940's (1941, 1943, 1940); 

 1944 was the last year of above-average production 

 and the first year of the recent decline; the 

 output fell below 50 percent of the 1929-43 

 mean for the first time in 1947. Even when data 

 are included for M-1 where the 1949 take was 

 above the 1929-43 average, the decrease from 

 1944 to 1949 amounted to 90.6 percent. 



ABUNDANCE IN STATE OF MICHIGAN 

 WATERS, 1929-49 



The estimates of the abundance or availability ' 

 of lake trout in the statistical districts of the State 

 of Michigan waters of Lake Michigan beginning 



Table 9. — Abundance indices for lake trout in Michigan 

 statistical districts, 1929-49 



[Percentages of 1929-43 mean] 



1 In the computation of the averages the abundance index for each district 

 was weighted by the percentage contribution of that district to the total 

 catch of all districts over the 15-year period 1929-43. 



with 1929 (table 9; see also figs. 3, 4, and 5), are 

 based principally on the records of the catch per 

 imit lift of large-mesh gill nets (mesh sizes 4K 

 inches and greater, extension measure). During 

 the base period 1929-43, large-mesh gill nets 

 accounted for 88.1 percent of the total catch of 

 lake trout. Set hooks were second (8.2 percent), 

 and poimd nets third (2.2 percent). The catch 

 of other gears plus a small quantity of lake trout 

 for which gear records were lacking made up the 

 remaining 1.5 percent (presentation here of 

 original data on gear composition of the catch is 

 not considered necessary). Poimd nets were of 

 sufficient importance to be included in the estima- 

 tion of abundance in only three districts (M-1, 

 M-3, M^). 



Records of the catch per unit of fishing effort 

 of large-mesh gill nets, set hooks, and pound nets 

 in the several districts in 1929-49 are given 

 in tables 10, 11, and 12. 



In the listing of the years of highest abundance 

 (middle section of table 8), as was true for the 

 years of greatest production (top section) , distinct 



' Argument about which of the two words should be employed would con- 

 stitute a futile quibbling over terminology. These estimates are based on 

 the fishing experience of the fishermen — the records of their catch of legal-sized 

 lalce trout per standard unit of fishing effort. They offer no uiformation on 

 the abundance of undersized lalce trout and are affected by such factors as 

 meteorological conditions, annual differences in the time of spawning in 

 relation to the fixed dosed season, and annual differences In the distribution 

 of fish. Yet, for all these obvious wealmesses they offer the best estimates 

 of abundance to be had at the present time. Accordingly, we do not hesitate 

 to use "availability" and "abundance" interchangeably. 



