134 THE LIFE OF THE SALMON 



and movements of marine creatures, including salmon, 

 and the forms upon which they feed, may be in some 

 slight degree different, but given these two con- 

 ditions an early run will be present. The main 

 circumstances of life in a small country like Scotland 

 are, however, practically the same. 



We may now regard the influence of temperature 

 upon the salmon when the mouth of the river has 

 been entered. In this connection there are two 

 aspects of the question which may be considered, 

 first the ascent of the main river, and second the 

 entrance of tributaries. Apart from the test of 

 temperature, it will be recollected that at the close 

 of the last chapter the results of marking clean run 

 fish were dealt with, and evidence produced to show 

 that such fish may remain two or three months in the 

 rapid lower waters of a river such as the Spey with- 

 out making material ascent. From the Tay similar 

 evidence was gathered, but the pause in the ascent 

 appeared to be less prolonged. In now extending the 

 range of observation, and considering the application 

 of the temperature test to this question, we are able 

 to see that there are other rivers in which this 

 pausing habit does not apparently obtain. The habit 

 of the early fish seems to vary considerably in different 

 districts. We have already noted that Tay fish ascend 

 to Loch Tay and remain there till May, when they 

 continue their ascent by entering the Dochart. As a 

 contrast to this we have early Ness fish passing quickly 

 through the short river Ness into the loch of the 

 same name (which is the deepest but one in Scotland), 

 but, unlike the Tay fish, passing on out of Loch Ness 



