60 THE AGE AND GBOWTH OF SALMON AND TEOUT. 



still further by comparing the aggregate age of trout that have 

 never been in the sea and of sea trout. The comparison works out 

 as follows: 



Two things are clear from this. In the river the number of individuals 

 decreases as we approach the maximum age of migration. In the sea it 

 increases from the minimum age of migration and decreases as we approach 

 the limit of the fish's life. 



The absence of females in the later year-classes in the river is 

 evidently due to the fact that they have migrated. 



Consequently the stock of fish that have never been in salt water 

 and the stock of fish that have migrated are supplementary to each 

 other. 



Similar conditions are met with in many of tfye streams to which sea 

 trout have access. If we examine the stock of fish that has never been 

 in the sea, we find that in many places males and females often occur in 

 equal proportion in the youngest year-classes, whereas the older year-classes 

 consist mainly, and at the end exclusively, of males. This must be regarded 

 as a sure sign that the stream in question chiefly contains fish that will 

 become sea trout. 



In many places, however, this is not so obvious, and in some streams to 

 which sea trout have access, we may even find that the proportion between 

 males and females is only slightly affected by age, and that spawning 

 females occur which have never migrated. 



Instances of such streams are Aagvand in R0d0herred, Nordland 

 (see Table XXL), Kvernvand in Naera, Namdalen (see Table XXIL), M01n- 

 bugtselv in Agdenes (see Table XXIIL), and the Os river near Bergen (see 

 Tables XXIV. XXVL). 



From these tables we are able to obtain the following comparison : 



