54 THE AGE AND GROWTH OF SALMON AND TROUT. 



A. Instances of Sea Trent and of the Rivers to which they 

 have Access. 



Sea trout, like salmon, spend the early years of their life in rivers 

 or fresh-water lakes. The duration of their stay there, before migrating 

 to the sea, varies just as it does for salmon, and the young smolts are 

 not all of equal age. 



This circumstance we can investigate in two ways. 



We can investigate the age of the young fish that live in the rivers, 

 and so get in certain cases an idea as to the duration of their stay there, but 

 we are faced here with a complication. For whereas no salmon attain any 

 considerable size before repairing to the sea, and as the females never, to 

 my knowledge, develop their ova before they migrate to salt water, we find 

 in many streams quite different conditions in the case of trout. 



In many streams where sea trout are found, trout may be met with which 

 attain considerable size and age and even maturity without having migrated 

 to the sea, and it is often very difficult therefore to say whether we are 

 dealing with the young of the sea trout, or whether the young fish we find 

 do not also include the offspring of fish that have never repaired to the sea ; 

 since by their outward appearance it is impossible to distinguish them. 



The scales of the sea trout, however, show growth conditions resembling 

 those of the salmon. In the river they develop slowly, in the sea extremely 

 rapidly. We can accordingly, in most cases, detect the boundary line on 

 the scale, which denotes the transition from poor to good growth, and 

 we can note the number of winters which the fish has completed prior to 

 migration. 



As I did in the case of salmon, so also with trout I have endeavoured 

 to obtain information by studying the scales with regard to the length of 

 time which the fish have spent in the river previous to migration. 



In Table XVIL, I have put down the results of an analysis of 192 sea 

 trout, taken from unsorted catches with the drag net that were sold to 

 a fish dealer in Trondhjem on June 26 and 27, 1909. 



This analysis has been worked out and arranged in the same way as 

 was done on page 28 in the case of salmon. 



If we take the results of this analysis, as regards age of migration, we 

 get the following : 



