48 THE AGE AND GROWTH OF SALMON AND TEOUT. 



to the percentage (see page 46). Here we see that the percentages of the 

 different age-classes vary from year to year, but we can only arrive at a 

 sound conclusion as to the extent of this variation by continuous investi- 

 gations spread over several years. 



What is the meaning of the greater age which we find in comparing 

 our examples from the north with the south ? Does it indicate that salmon 

 have a tendency to migrate northwards as they get older, or does it indicate 

 that northern salmon take longer to become mature, and that it is only 

 when they are older that they approach the coast and proceed up the 

 rivers ? 



It is impossible to reply with any degree of certainty, but the circum- 

 stances are exceedingly striking and deserve further study. 



I will only merely mention the fact that the materials I have collected 

 seem to indicate that both the above-mentioned factors may contribute 

 their share. 



As will be remembered in our discussions on the age of the smolts 

 before migration, and as to the occurrence of the spawning mark in reference 

 to age, we found the following facts. The smolts remain longer in the 

 rivers in the north than in the south, and if we investigate the age of fish, 

 when the spawning mark was first formed upon their scales, we find that 

 they must on the whole have been older, which moreover directly follows 

 from the fact that the stock of fish generally is older. After spawning, 

 the salmon, as far as we can discover (see page 39), also remains longer in 

 the sea in the north than in the south, before it returns to spawn for the 

 second time. It would seem as if all the functions of the fish are more 

 retarded the further northwards we go. Ordinary physiological considera- 

 tions would lead one also to expect this, and there can be little doubt that 

 this condition must to some extent make itself felt. 



In order to elucidate the question of the wanderings of the salmon I 

 have endeavoured to ascertain whether the markings carried out by Herr 

 Landmark afford any indications. These markings were almost all made on 

 spawning salmon, that is to say, fish whose chances of survival, in the light 

 of what we have discovered, could only be regarded as small. That is 

 presumably the reason why of the many thousands of salmon which 

 were marked so few fish have been subsequently recaptured.* 



* During the years 1893 to 1895, 6708 fish were marked in the rivers, principally 

 spent fish and kelts, and only 221 fish in all have been recaptured. Of these 221 salmon, 

 43 were caught again before they had migrated to the sea, 54 were recaptured in the sea, 

 and 112 on their return to fresh water, and in the majority of cases in the same 

 rivers where they were originally marked. During the same period 140 clean fish were 

 marked which were caught among the islands along the coast. Of these 23 were recap- 

 tured, and in all cases in the same season in which the marking took place. (Landmark, 

 " Merkning af Laks," Norsk Fiskeritidende, 1905, p. 487.) 



