ATLANTIC SALMON 



15 



ern Baltic and are again found on the same 

 feeding grounds as two-winter salmon in the 

 following autumn and winter. 



The salmon from the rivers of southern 

 Sweden and the opposite side of the Baltic 

 have no need to make migrations of any con- 

 siderable extent and move out only the req- 

 uisite short distance to the same grounds as 

 the salmon from the north. In these south- 

 ern rivers the average smolt age is low (80 

 per cent two years old). It gradually rises 

 in the more northerly rivers until in the 

 north of Sweden it is high (75 per cent three 

 years old). Yet in confirmation of the 

 marking results, the average smolt age of the 

 young salmon caught in the southern Baltic 

 is high (up to 70 per cent three years old) 

 and is built up by the very old Finnish as 

 well as northern Swedish fish. 



In Scotland clean salmon were first 

 marked in the sea in 1913 (Calderwood, 

 1913, etc.), and in Norway Professor Dahl 

 took up similar work in 1935 (Dahl, 1935, 

 etc. ) . For many years before these dates a 

 very considerable number of kelts had been 

 marked in the rivers of both countries, but 

 the isolated recapture of some of these, when 



again clean, in the sea has given only frag- 

 mentary information regarding the migra- 

 tions of the fish in salt water, and I do not, 

 therefore, at present intend to deal in ex- 

 tenso with them. 



The Scottish sea marking experiments 

 were started in the Moray Firth (Fig. 2) on 

 the northeast side of the country, were con- 

 tinued on the north coast, and during the 

 last two years, as well as in the present year, 

 they have been continued on the west coast. 

 Professor Dahl commenced the Norwegian 

 experiments at stations outside (but on the 

 coast of) the island belt near Bergen. He 

 has also operated a station inside the island 

 belt at the mouth of the Trondheim Fjord 

 and another station in the extreme north- 

 west corner of Arctic Norway on the island 

 of Soroy in West Finmark. 



In the course of the later Scottish and the 

 Norwegian experiments there has been a cer- 

 tain interchange of marked fish, and, for a 

 proper understanding of the results, it seems 

 to me that it will be better if they are con- 

 sidered as complementary and not as sepa- 

 rate entities. I propose, therefore, to deal 

 with the Scottish work from west to east and 



Fig. 2. 



