of the Fishery Board for Scotland. ' 71 



APPENDIX y. 



WATER TEMPERATURE IN RELATION TO THE EARLY 

 ANNUAL MIGRATION OF SALMON FROM THE SEA TO 

 RIVERS IN SCOTLAND. 



Paper No. 3. 

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



In my first paper on this subject I dealt with the thermal conditions of 

 the sea on the East and on the West Coast of Scotland, as compared with 

 the temperatures of such rivers as the Helmsdale, Brora, Thurso, Ugie, 

 Nith, and one or two lesser streams. The result deduced was that when 

 early-running salmon enter our rivers they leave a cold sea for a colder 

 river, and that therefore the contention that their ascent during the four 

 first months of the year is due to the attractions of warmer river waters is 

 not consistent with the actual facts of the case. 



In my second paper I compared the temperatures of the four leading 

 rivers of Sutherland, for which I had maximum and minimum daily 

 readings for a series of years. The results showed that the typical late 

 West Highland river Laxford did not, in temperature, differ in any 

 special way from the temperatures of such early rivers as the Helmsdale, 

 Brora, and Shin. 



Those two papers seem to me naturally to lead to the conclusion that 

 the presence or absence of an early or spring run in any river is not 

 primarily a question of temperature at all. I do not mean by this that in 

 an early liver a rise of temperature will have no influence upon the run 

 of fish, but I mean that in a river where no early run is at present found, 

 a rise of temperature will not cause an early run, and similarly that in an 

 early river the primary causal factor is not the prevailing condition of 

 temperature. In netting the river Tay for the purpose of marking 

 salmon during the close season of 1901-1902 {vide Ticeniieth Annual 

 Report of the Fishery Board for Scotland, Part 11, , p. 88) I was able at 

 the same time to make a few observations as to the ascending habits of 

 the salmon during the winter months. A quotation from the paper 

 referred to may perhaps be excused here, as explaining the part which 

 temperature seems to me to play in the ascent from sea to river. I am 

 not here dealing with the question of the ascent of tributaries from a main 

 river. " Fish ascending the Tay during November, December, and 

 "January, the period over which the observations here referred to 

 " extend, seem, so far as these observations indicate, to leave the brackish 

 " estuary for the river during times when either there has been a simul- 

 " taneous rise of water level and of temperature, or when there has been 

 " a rise of temperature unaccompanied with a rise of water level." The 

 netting during the close season 1902-1903 has again supplied evidence in 



