98 THE SALMON RIVERS OF SCOTLAND 



these are somewhat limited, being monthly means for 1888, 

 as compared with the Tay and Almond. It is interesting to 

 note the figures for the five first months of the year : 



Months. Earn. Tay. Almond. 



January . . 39-2 37-8 36-7 



February . . 35-7 37-5 34-4 



March . .37-1 37-4 34-7 



April . . . 42-8 43-6 37-3 



May . . . 49-9 46-9 



From these it would appear that during the early months of 

 this particular year, the Earn has greater fluctuations than the 

 Tay. As compared with the Tay, the Earn temperatures are 

 1-4 higher in January, and 3 higher in May, but slightly 

 lower in the three other months mentioned. The Almond, 

 it will be noticed, is consistently lower in temperature than 

 either the Tay or Earn. In this connection it is necessary to 

 state that the Earn readings were taken at Bridge of Earn, 

 which, as already seen, is within the tidal area ; so that it is 

 just possible that some influence of the Tay may have been 

 allowed to affect the results. But certainly from the limited 

 amount of data to go upon, there does not appear to be any 

 sufficient distinction in temperature to account for the absence 

 of Earn spring fish. A more important factor is perhaps the 

 predominating volume of Tay water, which acts as an induce- 

 ment to incoming fish to pass the mouth of the sluggish Earn. 



Tributaries entering the lower portions of large rivers are, 

 as a rule, passed by all early -running salmon ; but upper 

 tributaries, if supplied with good volumes of water, are entered 

 when their temperatures become approximated to the tem- 

 perature of the main river, or when their thermal conditions 

 are already relatively high. Temperature in this connection 

 must be treated in close association with volume of water. 

 The volume of the Earn is greater than that of many spring 

 rivers, and its temperature does not appear to be unduly low ; 

 but it has the Tay to compete with at its mouth, and for reasons 

 to be described it has an insufficient stock of fish. Between 

 Dupplin and Earn mouth the river winds about like the Forth. 

 At one point, near Forgandenny, a great loop has been cut 

 off, and in course of time other loops will no doubt be cut off. 

 As the crow flies, the distance to Dupplin is 9 miles, but by 

 the course of the river it is 14 miles. 



