54 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 29. — Average percentage of season's growth completed at various dates during the season hy age groups of the marked 



lake trout from the 1945 year class 



[The bases for the percentages are the increments of growth for full seasons computed from measurements of the scales of fish of the next higher ape groups of 



the same year class] 



' In order that age-group IV. which was represented in nearly all semimonthly periods, would not exert undue influence on the trend oidy those periods 

 which were represented hy one or more other age groups are included. 

 2 Based on the 13 fish in age-group VI. 



at 5 from mid-May through June. Beginning 

 with the first lialf of July, the percentages were 

 consistently smaller than those for age-group V 

 and, with one e.xception (early September), were 

 also below the percentages for age-group III. 



The erratic variation of the percentage of com- 

 pleted growth for age-group IV during September- 

 December can be attributed partially to the small 

 numbers of fish in the samples, but the generally 

 low level (61 to 83 percent; 75 percent for 4 lake 

 trout caught in late December) is further evidence 

 tliat the seasonal growtli was not completed at 

 the end of the calendar year. As the average 

 increment of growth of the 4 lake trout caught the 

 last part of December was only 2.0 inches, the 

 actual amount of growtli between December 31 

 (ages change on January 1) and the completed 

 growth of 2.6 inches at formation of the fifth 

 annulus was 0.6 inch. It was pointed out earlier 

 that the average estimate of the growth of age- 

 group IV for the entire season, calculated from 

 measurements of the scales of lake trout in age- 

 group V taken in 1950, was the same for fish 

 without the fifth annulus as it was for those that 

 had that annulus visible. However, the average 

 increment for 11 lake trout caught the first half 



of January, which did not have new gi-owth on 

 their scales, was only 2.3 inches (88.5 percent of 

 the total increment), whereas the average incre- 

 ment for an ecjual number of lake trout caught the 

 last part of the month was 2.59 inches (100 percent 

 of total increment). Increments for 4 fish taken 

 between the first of February and the 15th of 

 April were low (2.13 inches), but the average 

 increment for 12 fish taken the first half of May 

 (2.63 inches) showed a slight rise over that for 

 January. These few fish, caught January to May, 

 do not furnish definitely reliable information on 

 the end of tlie growing season, however they do 

 indicate that in certain years lake trout may 

 continue to grow tlirough the winter months. 



The 25 lake trout of age group V taken in Jan- 

 uary and February and a single fish caught in 

 early April had not started to grow. The incre- 

 ment of new growth on the scales of lak-e trout 

 captured in the last half of April amounted to 9 

 percent of the expected total increment, but this 

 percentage showed no clear tendency to increase 

 during May and June. A sharp upturn, beginning 

 in July, however, carried the percentage to 92 in 

 late September (with a single exception to the 

 trend in the first half of the month). The single 



