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 



