ON SALMON. 33 



The few which were forthcoming at the end were nearly all quite 

 small, and of the typical bluish brown and copper coloured shades, which 

 characterise the growing parr. The migration of the class of fish caught 

 in the earlier part of the month was apparently over. We tried in other 

 places but we did not find it worth while continuing. 



It is therefore not probable that there is any large migration during 

 the summer, though odd fish may occur. Examination of the central 

 portion of the scales of larger fish also shows that only a few have any 

 signs of summer growth in the river after the last winter prior to 

 migration. 



2. SALMON AFTEB MIGRATION. 



As I mentioned before, in dealing with the methods of investigation 

 which I have adopted, with the help of a microscope the scales reveal the 

 following facts. 



We can easily distinguish the boundary line which marks the entrance 

 into salt water. If we study the central portion of the scale (the river life) 

 with higher magnification we can count the number of winters the fish has 

 spent in the river. For example, compare Figs. 9b, Plate II., lOb, 

 Plate III., lib, Plate IV., which represent enlargements of the central 

 portion of the scales. 



Further, it can be seen how many winters the fish has completed in 

 the sea after migration, and also whether the fish has a spawning mark 

 or not. 



As an example of the methods I have adopted let us examine Table VIII., 

 which contains the analysis of 1612 salmon from Christiansand in the 

 season of 1909. As will be seen from the table, I have arranged the fish 

 according to their length in centimetres, and in a separate column I have 

 noted how many fish belong to each class. 



I have examined the scales of each class microscopically, and have 

 determined how long each fish has lived in the river prior to migration, 

 and how long it has lived after migration, and also whether it has previously 

 spawned (i.e., whether it has a spawning mark). According to the results 

 of this examination the fish have been classified under the various headings. 

 Fish which are returning to spawn for the first time are denoted in ordinary 

 figures, but those which show a spawning mark, and which have conse- 

 quently spawned on a previous occasion, are denoted in brackets. In the 

 same way each centimetre or length-class is dealt with in turn until the 

 whole are completed. 



The headings of the table are arranged so as to make it clear whether 

 the fish have completed one, two, three, four, five, or six winters subsequent 

 to migration. Under each of these main headings the fish are again divided 

 S.T. 3 



