AGE DETERMIXATIOX FROM SCALES OF LAKE TROUT 



00 



100 - 



90 



80 



5 



O 70 

 a. 



60 



50 



40 



30 



20 



I 



-o--o-^ 



JAN 



FEB MAR APR MAY JUNE 



J_ 



J_ 



_L 



J_ 



JULY AUG SEPT OCT NOV DEC JAN FEB MAR 



Fici RE 28. — PiTceiitage of season's growth of the marked lake trout from 1945 year class (the bases for the percentages 

 are the increments of the full season computed from measurements of the scales of the next higher age group of the 

 same year class). 



lak(> trout of ajio-tiroup V caught in Doccmhor, 

 however, liati compUUed only 58 percent of the 

 cxi)ecte(l total growth. 



A start of growth followed by a stoppage or 

 near-stoppage as demonstrated for age-group I\' 

 in the last half of April through May, and for 

 age-groii]) V in May and June, might he exiiecled 

 to produce irregularities in the scale structure. 

 Nevertheless, examination of the scales of lake 

 trout of age-groups IV and V captured late in the 

 growing season revealed no checks or marks that 

 could be attributed to this stoppage. 



Some of the irregtdarities in the data of table 20 

 can be attributed to the inadequacy of the samples, 

 but the majority give evidence that the coin-se of 

 the season's growth v'aries considerably from one 

 calendar year to another. (There is no evidence 

 of a ju'ogressive change witli age), '{"his year-to- 

 year \!iri(itioii iind the uncerlaiiit v as lo the tinu' 



growth ends (data were conflicting even among 

 the best represented age groups) prohibit a general 

 description of seasonal growth of the marked lake 

 trout. Growth may start as early as March or 

 as late as June. Once started, growth may follow 

 a regular course; but in sonu' years it may stop, 

 completely or nearly so, for a period of several 

 weeks. The end of the season as well as the start 

 probably varies from year to year. In some 

 seasons growth may continue into the next cal- 

 endar year. Because of the variation in the start 

 and finish of the growing season, growth of lake 

 trout in Lake Michigan is likely to occiu- in at 

 least 9 or 10 months of the year, i)ossibly in even 

 more. The most rapid growth, nevertheless, ap- 

 l)ears normally to take place in Jtdy and August. 

 The percentages at the right of table 29 indicate 

 that nearly half of the total season's growth occurs 

 in these months. The same set of figtn-es shows 



