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 
