AGE DETERMINATIOX FROM SCALES OF LAKE TROUT 



43 



turning more and more to cliul) fishing with tho 

 small-mesh nets. 



A gill net made of a single size of mesh tends to 

 catch the larger fish of the younger age groups but, 

 as the fish grow larger in later years this relation 

 between size of fish and size of mesh in the nets is 

 reversed and the net then catches the smaller 

 individuals of the older age groups. This reversal 

 takes place when the fish are at an earlier age if 

 small-mesh nets are used than if the fishing is done 

 with larger-mesh nets. The marked lake trout 

 of age-groups III and IV, caught in 2,'2-inch-mesh 

 nets, were 1.3 and 0.2 inches longer than tlie mean 

 calculated length for the age group, and those of 

 age-groups V and VI were 0.4 and 4.2 inches 

 shorter than the calculated lengtlis. Fish of all 

 age groups, caught in the 4/2-inch-mesh nets were 

 longer than those cauglit in the 2!2-inch-mesli nets 

 and also longer than the mean calculated lengths 

 for the age groups represented. The discrepancies 

 for age groups II to V fluctuated between 1.7 and 

 1.2 inches without clear trend. For age-group VI, 

 the difference (0.5 inch) was less than the other 

 differences, but the reduction mav not indicate 



that the reversal to capture of the smaller fish of 

 a year class was approaching for this net. Prob- 

 ably, larger fish were no longer available for 

 capture. 



Even though the large-mesli nets consistently 

 caught the larger fish, the average size of lake 

 trout taken in them and in the small-mesh nets 

 increased as the fish became larger. Nets of each 

 mesh size were static measures of a segment of a 

 changing range of lengths within the population 

 as the fish of each year class became older, hence, 

 the mode of the lengths of lake trout caught in 

 each net shifted from the lower toward the upper 

 limits of its segment as the average size of the fish 

 increased (table 21). 



T.\BLE 21. — Calculated lengths (in inches) of marked lake trout (year classes combined) caught in large- and small-mesh 



gill nets 

 IDifferences are shown below the lengths of flsh caught in each pair of nets) 



1 Size of mesh in net not recorded for 16 fish. 



* Fish caught :it clifTerent times during the growing season. Their total lengths :ire not comparable with llu- oalculatcd lengths. 



Calculated lengths of the marked lake trout 

 emphasize the differences in length between fish 

 caught in the 4}^- and 2j2-inch-mesh nets. The 

 differences increase in size with each year of life 

 (table 21, fig. 21). Undoubtedly, "the small 

 (average length at capture, 10.0 inches), slender 

 lake trout of age-group II captured in large-mesh 

 nets were caught by their teeth or by other en- 



tanglement in the twine. The size of the mesh 

 ill the net could scarcely have been the determining 

 factor in their capture. In fact, the small repre- 

 sentation from age-group II in the sample (that 

 from age-group III was six times as large) in- 

 dicates that the fish in this age group were too 

 small to be caught systematically in commercial 

 nets of anv mesh size used. Evidently, too, these 



