28 THE LIFE OF THE SALMON 



examination of sea caught salmon that herring and 

 sand-eels seem to be their favourite foods. Now 

 HerrDahl has caught the growing smolts out at sea 

 as they follow the shoals of their marine "supporters." 



Next we have to deal with the time spent by the 

 smolt in becoming a grilse before fresh water is 

 revisited. 



From the seasons at which young fish in the 

 transition stage have been taken, as compared to 

 their size and weight, as also from the early Tweed 

 returns, which must be regarded as reliable although 

 so few in number, it seemed certain that the view 

 very commonly held in Scotland on tins point was 

 erroneous, and that a full year in the sea elapses 

 between the time when the smolt leaves the river 

 and the time when as a grilse it returns. 



To obtain direct and reliable evidence on this point 

 it was desirable to mark a large number of smolts 

 by the attachment of some foreign substance. The 

 presence of small spring fish in many of our rivers at 

 the same time raised a problem which seemed likely 

 to be solved at the same time and by the same means. 

 In 1903 I had experimented at Fochabers Bearing 

 Ponds as to a suitable mark for attachment. A 

 small silver disc was attached by a split silver pin to 

 the gill cover so that it lay flat upon the outside 

 and yet gave room for the necessary expansion. 

 The delicate bones of the smolt's operculum could 

 not, however, stand the strain of this mark, and in j 

 a few weeks very many of the marked fish had 

 dropped both disc and pin by the rupture of the 

 gill cover. 



