of tJie Fishery Board for Scotland. 



77 



APPENDIX VI. 



THE TEMPERATURE OF THE RIVER TAY AND ITS TRIBU- 

 TARIES IN RELATION TO THE ASCENT OF SALMON; 



By W. L. CALDERWOOD, F.R.S.E. 



As a natural accompaniment to the preceding paper, which deals with 

 the ascent of early-running fish from the sea to fresh water, and with the 

 accumulation of early fish in certain well-defined parts of a river system, 

 I desire now to notice the bearing which temperature seems to have upon 

 the salmon's ascent of tributaries, in so far as this may be gathered from 

 a study of the district of the river Tay. 



The curves of weekly mean temperature presented in the accompanying 

 chart include the readings for the lower portion of the river taken at or 

 near Perth, which in the preceding paper were compared to the Nith 

 readings, and also curves for the upper main river at Grandtully, and for 

 the tributaries of the Garry and the Lyon. 



The Perth readings were taken by Mr. Lumsden, the Superintendent of 

 the Tay Fisheries under the District Fishery Board. For the other 

 temperatures I am indebted to the kindness cf my friend Mr. H. W. 

 Johnston, who from Grandtully was good enough not only to take 

 readings himself, in continuance of the practice he has carried on for many 

 years, but to arrange that temperatures be also taken in the Garry and 

 the Lyon. In studying this chart, the first feature noticeable is that the 

 Garry (Perthshire) is constantly lower than the Tay and the Lyon. The 

 dotted black line is at once seen to be always below the three other lines. 

 This is distinctly interesting, since the Garry is the late tributary of the 

 upper Tay. The Garry, after passing through Killiecrankie, joins the 

 Tummel at Faskally — than which it is also rather colder — and the 

 Tummel flows into the Tay below Ballinluig. Grandtully is on the 

 main river above Ballinluig, and the Lyon enters the Tay above Grand- 

 tully. After the influx to the main river of such cold streams as the 

 Garry and Tummel, and in view also of the fact that the Almond, lower 

 down, is another cold and late tributary, although in low conditions of 

 water-level all the water of the Almond is carried off to below Perth by 

 the Perth Lade, we are not surprised that, of the two curves showing main 

 river temperatures till April, that for Perth is the lower. Loch Tay is 

 14^ miles long, has a maximum depth of 508 feet, and a mean depth of 

 199 feet ; and to give some conception of the amount of contained water 

 it has been recently estimated that *' if the water of the loch could be 

 " placed in a cubical receptacle it would require to be 1279 yards (nearly 

 " three-quarters of a mile) in length, breadth, and height." * The water 

 which flows from this large loch is naturally much more uniform in 

 temperature than is the water in the majority of the tributaries. The 

 temperatures of the Tummel were taken above the junction of the 

 Garry, i.e., on the Bonskeid side of the river between the falls of 

 Tummel and the junction. 



The following Tables of Tay records, for which I am indebted to Mr. 



* The Survey of British Lakes. Article by Jas. Chumley, Scot. Geo. Mag. August 

 1902. Vol. xviii., No. 2. , ° 



