PARR AND SMOLTS 105 



season. On August 13, 19 14, I caught in Loch Lomond a fish which 

 was clearly a sea-trout smolt on its way to the estuary. It measured 

 gj inches in length, was 4.^ inches in girth, and its scales came off freely 

 in handling. When sending some of the scales for examination to Mr. 

 Hutton I noted briefly : — "A very interesting fish as being apparently 

 a very late-running smolt. Four parr marks still visible towards the 

 tail on the scales being removed." I reproduce a photograph of one 

 of the scales (Fig. 30), which indicates that the fish had completed four 

 winters' residence in fresh water before the migratory instinct asserted 

 itself in its fifth year.^ 



Weather conditions affect considerably the time of descent of the 

 main body, and where the stock is large and distributed throughout a 

 great stretch of country inland, the run will be proportionately pro- 

 longed. It is, I think, always prolonged where an extensive estuary 

 receives the inland waters through long tidal reaches. The descent 

 under these circumstances is a very leisurely affair, or it might be said 

 that once in brackish water the smolt is in no haste to go further afield. 



It is a curious fact, worthy of special observation, that the descent 

 of the main body of sea-trout smolts in the river Leven always precedes 

 the main descent of the salmon smolts by about a fortnight, and I 

 understand, for I have made inquiry, that this order of progression to 

 the sea obtains elsewhere. 



So far as I am aware, no investigations equivalent to those under- 

 taken by Mr. Knut Dahl in Norway have been attempted in Britain 

 with a view to determining when the young sea-trout first migrate to 

 salt water as sea-trout smolts, whether in the first, second, third, or 

 even some subsequent year of their existence. This appears to me to 

 be a vital question in the life-history of the fish and one deserving of 

 the fullest and most careful investigation in many rivers. I have not 

 myself made any such extensive investigation, and can only submit 



1. See later as to this subject, pa>je 110. 



