56 THE AGE AND GEOWTH OF SALMON AND TROUT. 



can now classify the sizes according to the different age-classes which 

 migrate. Each of these classes, as will be seen, has its own limits of 

 variation, the average size invariably increasing with age. 



It is also worth noting that some of the fish which migrated at a later 

 period of life appear to have been of considerable size when they left the 

 river for the sea. 



If we now turn our attention once more to Table XVII., we find, as was 

 the case in the corresponding tables for salmon, valuable information 

 regarding the fish after its first journey to the sea. 



It must be remembered that the table only refers to saleable fish. The 

 limit below which fish are unsaleable is about 20 cm., so that the majority 

 of the young fish which migrated in May and June for the first time 

 in their lives are of course excluded. We merely get a few of the largest of 

 them in the first group, i.e., those which have not completed a winter after 

 migration, and which consists of those sea trout that have just quitted 

 the river. It follows that neither number nor average size in the case 

 of these fish is of any quantative value for determining the total stock. 

 On the other hand, the older groups (one winter, two winters, three winters, 

 etc., after migration) are fully represented in the catches, and both numbers 

 and sizes have therefore a definite value for determining the composition 

 of the stock and the growth of the fish. 



Summarising the information obtained from the table we get the 

 following : 



In the matter of the numbers of individuals in each age-class there is 

 here much that reminds one of what we found in the case of salmon, The 

 sea trout caught by the nets consist mainly of fish that have lived from one 

 to four winters subsequent to migration, fish of higher ages occurring only 

 exceptionally. At any rate, in my search for large sea trout I have rarely 

 met with individuals that had attained greater age. 



What value must be ascribed to the relative distribution of the whole 

 stock among these four age-classes is another question. It is quite probable 

 that other samples may show higher figures for the older classes, Still I 

 feel quite convinced that the older classes are generally characterised by a 

 diminishing number of individuals. The bulk of the sea trout brought to 



