18 SALMON-FISHERY OF SCOTLAND. 



When Nature, then, or rather Nature's great Author, formed 

 all these varieties of the salmon race, and planted one in each 

 river, it was certainly not that they should be all lost by pro- 

 miscuous intermixture ; and he, therefore, engrafted instincts 

 into them, sufficient for perpetuating what he had made. By 

 the gregarious instinct, each variety, or tribe, is made to shoal 

 by itself, unmixed with other varieties, even in the sea ; and 

 by another powerful instinct, all are made to return from their 

 migration, with perfect regularity, to their native rivers ; by 

 which means the whole varieties of the race have been con- 

 tinued as they were originally formed. And it is the same 

 with herrings, of which each loch has its own variety or distinct 

 breed.* 



If salmon entered rivers by chance, it is plain that they 

 would all go into the first river they met with, if all could get 

 into it without choking up its course, and that the rivers in 

 remote situations would have none ; or a river might be full of 

 fish one year, and be quite deserted the next without even a 

 breeder. How different this from the manner in which all now 

 get regularly their share, in consequence of the instinct which 

 brings the fish back to their own rivers. A straggling fish of 

 one river, may, no doubt, sometimes go into another, because 

 the organs of a salmon may be. .diseased as well as those of 

 another animal ; but this seldom occurs. It may also happen 

 sometimes, that when a shoal or tribe of salmon are scattered, 

 either by their natural enemies, or by stake-nets placed on their 

 course, when returning to the rivers, a stray fish belonging to 

 one river may mix with and follow a shoal belonging to another 

 river, as a stray sheep will sometimes mix with a flock of 

 passing sheep ; but even if the salmon should accompany the 

 strangers into their own river, he would soon leave it, if not 

 killed, and return to his own. We have heard an instance of 

 such a salmon being taken and marked, and allowed to escape, 

 and retaken in his own river next day at a distance of forty 

 miles. 



We know that some salmon-fishers, whose experience has 



* There is not, too, a trout loch or stream in Great Britain, or, as Sir H. Davy 

 remarks, in Europe, that has not its own variety of the trout species. 



