THE SALMON AND WATER TEMPERATURE 127 



perature in relation to salmon fisheries I write 

 exclusively of Scotland — we may say broadly we 

 do not find a regular run of spring fish in small 

 rivers, even although these rivers are well stocked, 

 and pure, and in no way over-fished. In rivers of 

 moderate size we, for the most part, find only 

 occasional runs of rather late spring fish. But in 

 the larger and more important rivers, Tay, Dee, 

 Ness, Beauly, Brora, Helmsdale, Thurso, Naver, we 

 have regular and steady runs of spring fish. In these 

 rivers also we have, besides considerable volume of 

 water, comparative purity — in the Highland rivers 

 named we may say complete purity — and an apparent 

 absence of over-fishing. In a river like the Tweed 

 there is too much netting to allow of the entrance of 

 many springers, or of their passage upwards to the 

 safer head waters. Other rivers might be mentioned 

 which like the Tweed should, in my opinion, have 

 many more spring fish ; but to mention individual cases 

 would be to depart from the question of temperature. 

 The fact that the first-class rivers above named 

 flow either to the east or north has suggested the 

 theory that the cause of the early entrance of salmon 

 lies in the fact that the sea on this side of the 

 country — the North Sea — is a colder sea than the 

 Atlantic Ocean on the west coast, and that the 

 rivers, flowing, as many of them do, through long 

 stretches of not very high land, are comparatively 

 warm, being free from the great admixture of snow 

 water which in spring passes off" from the high West 

 Highland hills, and that the salmon therefore prefer 

 to leave this cold North Sea at an earlier time than 



