34 



FISHERY BITLLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 13. — Length-frequency distribution of "marked" lake 

 trout at capture, in age groups indicated by deformed or 

 missing fin (all year classes combined) 



[Fish in "yes" column of cacli ago group are those tor which age read from 

 scales agreed with age indicated by abnormal fin. and fish in the "no" 

 column are those for « hich ages disagreed. Total lengths in inches] 



I Later age groups not included because the number of fish in each was too 

 small to Yield useful information. 



' No fish were captured for which the age read from the scales agreed with 

 this supposed age. 



the lengtlis and the progressive shift of modes and 

 means of fish in the "Yes" cohimns are much as 

 would be expected. The frequencies in the "no" 

 columns do not exhibit a similarly consistent rela- 

 tionship. They show a random scatter greater 

 than that which can be ascribed to the small num- 

 bers of fish. Modes are lacking, and the means 

 give no indication of the progressive increase in size 

 that should accompany increase in age. The dif- 

 ferences between the two groups with respect to 

 indicated growth is demonstrated by the summary 

 in table 14. Here, as was true for fish from south- 

 ern Lake Michigan, the lake trout for which there 

 was disagreement on age present the ridiculous 

 spectacle of diminishing length with increase in age. 

 A high percentage of tliem obviously could not have 

 been from plantings of marked fingerlings. 



Another approach to the question of the presence 

 of unmarked lake trout in the samples lies in the 



comparison of the growth of lake trout for which 

 there was agreement on age with the growth of 

 thosef or which there was not agreement on age. 

 In this comparison it was assumed that none of 

 the lake trout for which there was disagreement 

 were marked fish and that the scales rather than 

 fin abnormalities offer the correct estimate of age. 

 Table 15, which gives the result of this compari- 

 son, is so arranged that the vertical columns give 

 the average lengths at ages indicated by abnormal 

 fins and diagonal rows (from upper left to lower 

 right) contain a series of estimates of the length 

 of lake trout of the same age, as read from the 

 scales. As would be anticipated, if the readings 

 are correct, the lake trout with agreement on age 

 were shorter than those whose ages, read from the 

 scales, were one or more years older than the 

 ages indicated by the deformed fins. Conversely, 

 the lake trout with agreement on age were larger 

 than others whose ages were read one or more 

 years younger than the ages indicated by the fins. 

 In general, the magnitude of this difference in 

 lengths was progressively greater with each in- 

 crease in tiie number of years of disagreement 

 between the supposed age of the fish and the age 

 read from the scales. Despite the considerable 

 variability expected because of the small numbers 

 of fish in some samples and the known large range 

 of lengths within age groups, the means in each 

 diagonal, in the main, fluctuate normally about the 

 average length determined for lake trout for whicli 

 ages from scales and fin marks agreed. 



Data in summarj- table 16 support the conten- 

 tion that lengths of age groups determined by 



Table 14. — Comparison of average lengths of lake trout, for 

 which the ages as indicated by scales and fins were the same, 

 with average lengths as indicated by abnormal fins of lake 

 trout for which ages indicated by fins and scales were 

 different 



[Data from table 13. Number of fish in parentheses] 



