INTRODUCTORY REMARKS. 43 



rivers, are subject to constant fluctuations in their 

 productive powers, arising among other reasons from 

 the fact that one class of fish depends for food upon 

 the breeding capabilities of others. It may be as- 

 sumed that whenever the enemies of one race eat up 

 and destroy the excessive numbers of another, the 

 supply of those so destroyed will be diminished there- 

 by, until particular localities become so denuded, that 

 the fish disappear for a time, or until reproduced in 

 the course of nature. This we know to be the case 

 in some streams that have become salmon rivers, in 

 which there had been previously an excessive quan- 

 tity of trout. As the trout spawn a few weeks before 

 the salmon, we may assume the salmon, in the con- 

 struction of nests for hatching their young, have 

 grubbed up the trout beds, and deposited their own 

 in the same locality. Be that as it may, in a few 

 years these trout streams have been converted into 

 salmon streams. 



This occurred a few years ago in the tributaries of 

 the " Clare" Galway river, and this may be considered 

 a fair illustration of what is probably constantly tak- 

 ing place elsewhere. 



Since fish live upon fish food, their powers of re- 

 producing their species are wisely ordained to be such 

 as to keep up the balance of nature. 



I will now mention what I consider a proof that 

 the race of salmon do not escape from nature's law of 

 destruction. My friend, Mr. R. Buist, of Perth, and 

 myself, in the year 1852, ascertained from a statistical 

 account of the salmon produced from the River Tay 

 one of the chief salmon fisheries in Scotland the 

 following remarkable conclusion : 



Estimating the annual migration of fish up and 

 down the river adopting a fair standard as to the 

 number of breeding fish, and the quantity of ova an- 

 nually deposited in the beds of these streams in pro- 



