ON SALMON. 



47 



absolutely representative of the general stock of fish in each year, but 

 taken together they leave no doubt that the salmon in East Finmarken 

 are distinctly older than those in the neighbourhood of Trondhjem. 



Our investigations therefore seem to indicate clearly that the salmon 

 caught in the north are, on the average, considerably older than those caught 

 farther south, and that this is one of the chief reasons of the difference in size 

 which has so long been recognised. 



Let us now inquire whether the average weight of the various year 

 classes can also be regarded as a contributing factor to the difference in the 

 size of the fish in the various districts. For this purpose we may compare 

 the average weights previously given in the table on page 40. 



As we see from this table, there is some difference in the average 

 weight of salmon of the corresponding year-classes in the different localities. 

 Possibly this is due to an actual difference in conditions, or it may be that 

 it is merely the result of chance. With so rapidly a growing fish as the 

 salmon, the date of capture must have an important influence on the 

 average weight ; and for this reason, when instituting a comparison between 

 the different localities, we must not place implicit confidence in the results 

 obtained. 



As we see, the difference is not so great, nor is it sufficiently regular to 

 explain fully this variation which we have previously shown to exist in the 

 various districts (cf. page 43) even though it may possibly be a contributing 

 cause. 



In the same way we notice in the tables an annual variation in the 

 average of salmon belonging to the same year-classes. This is, however, 

 not important enough to explain the large annual variations which we 

 found in the average weights of fish over 3 kilos. (See page 44.) 



It is most probable that annual variations in age-composition in this 

 respect play a very important role. That such variations do exist is appa- 

 rent if we examine the tables in which the age groups are arranged according 



