THE SALMON AND WATER TEMPERATURE 141 
weekly means for the Tay at Perth and at Grand- 
tully, and for the Lyon and Garry, is given in 
Part II. of the Twenty-first Fishery Board Report, 
and it seems unnecessary to enter here upon a 
detailed account of the readings from each locality. 
In general terms the results show, as compared to 
the main river, the Grandtully curve of which is 
comparatively high, that in descending order of 
temperature we have first the Lyon, then the 
Tummel, and last the Garry. It is therefore of some 
interest to realise that early fish in ascending the 
Tay are found on the opening of the angling season, 
January 15, not only in the loch, but in the river 
Lyon, which, as we have seen, has a temperature 
closely approximated to that of the upper Tay and 
loch. Next, a limited number of fish are found to 
be already entering the mouth of the Tummel and 
pausing in the deep pools of Easthaugh Water there, 
but that as the temperature of the colder Garry 
rises so as to approximate to that of the Tummel, 
fish more freely ascend the Tummel and then enter 
the Garry. This last emigration does not usually 
take place till April, although a few fish may be 
found in the deep pools of the Pass of Killiecrankie 
in March. Moreover, in unusually warm springs, 
when all the tributaries are, as it were, advanced in 
temperature, the times at which fish ascend are, 
while unaltered in order of river, earlier in point of 
season ; and conversely in cold seasons the stock of 
early fish is delayed in their ascent of the tributaries, 
If therefore in early winter much snow lies on the 
hills drained, say, by the Lyon, so that that river 
