52 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 27. — Average weight (ounces) of marked lake trout 

 at time of capture 



I Weights of the 13 fish in age-group VI omitted because only 5 fish were 

 weighed and the data are too scattered to he of value in this table. 



More dependable data on the progress of the 

 season's growth may be obtained by romputation 

 of growtli from scale measurements. Examples of 

 the distribution of these increments are contained 

 in the records for the 555 lake trout of age-group 

 IV from the 1945 3'ear class, the largest year class 

 in the collections. Their increments of growth in 

 length were computed by semimonthly periods 

 (table 28). 



The amount of growth attained by individual 

 lake trout in any stated time varied widely. By 

 the end of April, the range in the amount of 

 seasonal increment of growth in length was from 

 nil to 1.4 inches. This range continued nearly 

 constant and the mean advanced only slightly 

 (0.14 to 0.40 inch) until the middle of July." 

 In the latter part of July the range in lengtlis of 

 the increments began to broaden and by the end 

 of August the spread was 2.8 inches. In the fore 

 part of August, some lake trout were still just 

 beginning to grow whereas others had been grow- 

 ing since the middle of March or possibly even 

 longer. It was largely because of this wide 

 spread in the time of the onset of growth that the 

 average increment was still only 0.22 inch in the 

 first half of June. Subsequent more rapid in- 

 crease carried the average to 1.7 inches in the 

 first half of September. Returns of lake trout 

 were so sparse during the remainder of the year 

 that dependable estimates of growth cannot be 



» iMp,v growth cannot be recognized on the scales until the first circulus haS 

 been formed, a circumstance which probably accounts for the small propor- 

 tion, at any time, of fish having as little as 0.2 inch caclulated growth. The 

 smallest calculated length increment is more often 0.4 inch. Hence the fish 

 usually had grown nearly \i inch by the time the annulus could be read with 

 confidence. 



made from them. It is especially difficult to form 

 a judgment as to the time the season's growth 

 ends. It appears from the data in table 29 that 

 the growth of the fish in age-group IV had not 

 been completed by the end of December, when the 

 average increment (4 fish) was 1.95 inches or 0.64 

 inch below the figure of 2.59 inches computed for 

 the full season from age-group V of the same year 

 class. (The fish in age-group V that had not yet 

 completed the fifth annulus gave nearly the same 

 estimate of growtli in the fourth year, 2.60 inches, 

 as did those on whose scales the fifth annulus was 

 visible, 2.58 inches.) 



Records of tlie percentage of the season's 

 growth completed by age groups of the 1945 year 

 class up to various dates of capture, despite gaps 

 in the data and the siaall numbers of fish on which 

 certain percentages were based, give evidence of 

 annual differences in tlie progress of growth and 

 of irregular growtli in some years (table 29). 

 These points are well illustrated by the curves in 

 figure 28 which were fitted by inspection to the 

 empirical data. 



The data were scanty for the lake trout of the 

 1945 year class in age-group II. The single trout 

 captured in the first half of June had made no 

 growtli. Percentages of growth completed by fish 

 caught later in the season rose quickly to 51 in 

 early August but fluctuated erratically thereafter. 

 Seven fish recovered in December had grown more 

 (percentage, 115) than the "expected" increment 

 for the full season calculated from measurements 

 of the fish in age-group 111. 



The 4 lake trout of age-group 111 caught in late 

 April and early May 1948 exhibited no new 

 growth, but those captured during the last half of 

 May had completed 7 percent of the expected 

 growth for the season. The percentage dropped 

 ill early June, but thereafter it increased steadily 

 (except in the first half of September) to 94 per- 

 cent in early October. The single trout caught 

 in December had gained only 79 percent of the 

 expected total increase. 



Age-group IV, captured in 1949, seems to have 

 started growing early in the season. Possibly the 

 single lake trout with new growth in January could 

 be dismissed as aberrant, but all semimonthly 

 collections from the latter half of March onward 

 contained some fish that had begun to grow. The 

 advantage of this early start was later lost, how- 

 ever, for the percentage of new growth remained 



