CHAPTER VI 
THE SALMON AND WATER TEMPERATURE 
Early and late rivers—Rivers made late by man—Tempera- 
ture of the sea round Scotland—Temperatures of early and 
late Scottish rivers—Temperature of water no indication of 
seasonal character—Effects of temperature on fish ascending 
rivers—LHarly runs of fish in upper waters, Garry and Orchy 
—Effects of cold water upon ascending fish—The entrance 
of tributaries from main river—Rapid ascent of summer fish 
—Sea lice may remain attached for four or five days 
THE theories which have been advanced to explain 
the diverse seasonal runs of salmon into fresh water 
—why in some rivers there should each year be 
early runs of fish, and in others only late runs— 
have, with I think one exception, been based upon 
considerations of water temperature. The exception 
is the ingenious but unsupported theory of the late 
Frank Buckland, that the seasonal character of a 
salmon river depends on the length of the river in 
proportion to the square mileage of its drainage area. 
At the outset, in the consideration of this question, 
T would point out that we are at the present day by 
no means certain that the real seasonal character of 
some rivers can be properly interpreted by the exist- 
ing conditions. Certain rivers are described as late 
rivers, and have no doubt been found to be late 
