70 Appendices to Twenty- ourth Annual Report 



APPENDIX IIL 



AUTUMN MIGRATION OF SALMON SMOLTS IN SCOTLAND. 



ByW. L. CALDERWOOD. 



In my last Annual Report (Appendix III.) I dealt with the seaward 

 migration of smolts in the spring as observed by the aid of certain 

 netting operations, both with a small-mesh sweep net and with a 

 sparling net lowered from a smack moored in the Tay estuary. The great 

 abundance of smolts congregating in the neighbourhood of Kinfauns, 

 where the first trace of marine influence seems to be felt, was referred 

 to, and by the use of the sparling net in the lower estuary the difference 

 of habit between the salmon and sea-trout smolt was apparently ascer- 

 tained in the rapid descent to the open sea on the part of the salmon as 

 contrasted with the lingering estuarial habit of the sea trout. 



Since the time when Shaw at Drumlanrig proved that parr and 

 smolts are the young of the salmon, the significance of the spring 

 migration to the sea of shoals of smolts has been recognised. Num- 

 erous observations have since been made to ascertain the age and 

 growth of smolts previous to the seaward migration, and the generally 

 accepted view at the present day undoubtedly is that in our country 

 the great majority of salmon smolts leave the river for the sea when 

 they are 26 months old or thereby, but that some go a year earlier and 

 some a year later. The famous Stormontfield experiments have largely 

 guided opinion on this point, and from these it has been estimated that 

 8 per cent, migrate the first year, 60 per cent, the second year, and 32 

 per cent, the third year. It has to be understood, however, that this 

 statement refers to the British Islands, and not apparently to other habitats 

 of S. solar, such as Norway and the American Continent. It is accepted 

 on all hands that the greatest annual migration of smolts takes place in 

 spring. Further than this, it has, however, been ascertained by a 

 limited number of observers that smolts also migrate seawards in 

 autumn and winter, and probably to some extent all through the year. 

 On this point information from Scotland has been practically absent. 

 Many writers, it is true, have referred to parr as being found at all 

 seasons, but it is by no means clear that the references were to fish 

 sufficiently advanced to be in the migratory condition, although the 

 name parr has sometimes been employed to describe the little fish with 

 silvery scales usually called smolts. In England, Murie, Proc. Zoo. Soc, 

 1870, states on the authority of Bucklana f hat " there is good evidence 

 " of a second migration of smolts in the month of September." Willis 

 Bund, Salmon Problems, p. 60, maintains that in a well- stocked salmon 

 river the time when smolts of various stages descend depends upon 

 various conditions, and that no hard and fast rule can be laid down ; 

 and on p. 9 of the same work he describes finding silvery scaled samlets 

 in eel traps in the Severn in December 1884. Day, Fritish and Irish 

 Salmonidfv, p. 90, states as a fact that migrations occur in the autumn 

 il as well as probably throughout the year." From time to time refer- 



