68 THE AGE AND GKOWTH OF SALMON AND TROUT. 



may be due to several causes. On the one hand, it may be ascribed, 

 perhaps, to insufficient material, though with waters so simple in character 

 as Chaigijok and Krokaa this is not a matter of much consequence. On the 

 other hand, it may possibly be due to matters connected with migration and 

 mortality. 



A third point of interest is the relatively small maximum age in such 

 small streams as Krokaa. 



As will be seen below in the statement of the average sizes of fish at 

 different ages, this is different in all three places, though there is most 

 resemblance between Krokaa and Chaigijok, where growth is slow. In waters 

 like these, where development is so tardy, it is sometimes difficult to 

 decipher the scales of the older fish, and it is possible, accordingly, that we 

 may occasionally assign too low an age to some of them. 



But this can hardly be of any great consequence, since the scales of 

 many of the oldest fish are quite easy to decipher, and are without the 

 thickened, irregular edge which characterises the scales of fish whose growth 

 has practically stagnated. 



A similar low maximum age was apparent in almost all the lakes and 

 streams which I have investigated in which the fish did not run large. 



We may take as an example the sea trout streams, which I have 

 previously described, where we found a short term of existence (or 

 residence) combined with relatively poor growth. In these we ascertained 

 that in certain cases migration could clearly be assigned as the cause of the 

 low maximum age, and the same reason may also to some extent be 

 effective in the small inland waters where there are young, slowly -growing fish. 



Most of the waters where growth is more vigorous are characterised 

 also by older fish. 



In the accompanying table I have compared the calculated mean values 

 of the lengths of the fish in a number of lakes and streams.* 



We can thus compare directly the length of fish of identical age from 



* See Tables XXVIII. , XXIX., XXX., XXXI., XXXIL, XXXI Vs., XXX Vs., 

 XXXVI., and XXXVII. 



