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 tothe 
safer head waters. Other rivers might be mentioned 
which like the Tweed should, in my opinion, have 
many more spring fish; but tomention 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 
