PARR AND SMOLTS 105 



season. On August 13, 1914, 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 handUng. 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 

 1 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, page 110. 



