130 SALMON AND TROUT. 
lake rivers are beginning to fail. Of these operating causes 
two of the Sutherland streams afford good examples. One, 
the Oikel, springs from a small exposed alpine pool some half 
mile in breadth ; the other, the Shin (a branch of the Oikel), 
takes its rise in the deep sweeping waters of Loch Shin and its 
tributary lakes. The Shin joins the Oikel about five miles 
from the sea. Early in the spring, all the salmon entering this 
common mouth diverge at the junction, pass up the Shin, and 
thus return, it would appear, to their own warmer stream ; 
whilst very few keep the main course of the Oikel until amuch 
later period. 
Nor does it appear that these operative causes and their 
resultant effects are confined to Scotland. An analogous 
instance, indirectly traceable to the same cause, has been 
pointed out by Dr. Heysham, in his ‘Catalogue of Cumber- 
land Animals,’ as observable in several of the rivers of that 
county: The salmon, during winter and spring, evidently 
prefer the Eden to either the Esk, Caldew, or Peteril, although 
the Eden and the Esk pour their waters into the same estuary, 
and, in fact, are only separated at their mouths by a small 
promontory. There is hardly an instance, Dr. Heysham 
asserts, of a salmon entering the Esk until the middle of April 
or beginning of May—a circumstance always referred by local 
fishermen to the difference in temperature between the two 
streams. The waters of the Eden, they allege, are consider- 
ably warmer than those of the Esk, which, from the shallow 
and rocky character of the bed of the Esk, appears not im- 
probable. 
Be this as it may, it is an indubitable fact that snow water 
prevents salmon from running up even the milder stream of 
the Eden. 
The Caldew and the Peteril, again, pour their waters into 
the Eden, the one at, and the other a little above Carlisle; 
yet up neither of these rivers do salmon ever run, unless at the 
spawning season, and then but in small numbers. 
The rule, however, which would appear to be inferred from 
