48 THE LIFE OF THE SALMON 



fish seems still uncertain. It is significant, more- 

 over, that in these Siberian rivers the local species 

 of Coregonus, which with us are purely fresh water 

 fish (the vendace and powan), are fully migratory, 

 as reported by Giinther. It is quite possible to 

 imagine that in early times salmon were so numerous 

 in our rivers that a suitable supply of food was 

 impossible, and that therefore the habit of migrating 

 to the sea developed, but this is a mere supposition. 

 As a matter of natural history it is, on the other 

 hand, I think, more in harmony with what is known 

 of the habits of the other members of the group to 

 suppose that the habit which has developed is that 

 of migrating to fresh water primarily for the purpose 

 of spawning, and that in large continental rivers 

 and in rivers of land now disconnected from conti- 

 nents the habit of remaining for long periods, and 

 by some species of living more or less permanently, 

 has been acquired. 



If, however, as I have shown, it happens that in 

 some seasons in our islands salmon ascend our 

 rivers in comparatively poor condition, a serious blow 

 is struck at the view that the primary cause of 

 ascent from the sea is the state of satiety. Along 

 with the procuring of food, the other great instinct 

 is that of reproducing the species, and a fish not 

 up to the normal standard of high nutrition may 

 still be impelled by this instinct, even if the repro- 

 ductive elements are, it may be, unable to produce 

 eight or nine hundred eggs per pound weight of fish. 



I have dealt with this point of the marine as 

 opposed to the fresh water origin of Salmonidae, 



