The Natural History of the Salmon. 63 



same individual may change the salt or fresh 

 water several times in the year. 1 However, this is 

 the case in certain rivers only, for instance, in those 

 falling into the Moray Firth ; in others one immigra- 

 tion only is known to occur. The cause of the 

 irregular ascents previous to the autumnal ascents 

 is unknown. A part at least of the hybrid fishes 

 retain the migratory instinct ; but it is not known 

 whether sterile individuals accompany the others 

 in their migrations. 



"5. It is said that the migratory species invariably 

 return to the river in which they are bred. Experi- 

 ments have shown that this is normally the case, 3 

 but a small proportion appear to stray so far away 



1 It is a well-known fact that they do ; observers have 

 noticed that after a long drought, numbers of fish go down to 

 the sea on the first flood from the pools within a reasonable 

 distance of the salt or brackish water. (H.) 



2 An exemplification of this occurs yearly at the junction 

 of the Rivers Lochy and Spean. The former river at the 

 junction has a high fall, and it is only when the Spean has 

 risen to a certain height, that the fish can get up these falls 

 into the Lochy proper, and so into the Loch. The salmon 

 in great numbers lie here waiting for this flood ; not one 

 will go up the Spean, to which there is ready and easy access ; 

 and very few will go up the artificial salmon ladder, which 

 at a great expense has been prepared for them. But the 

 moment the Spean comes down in spate, which it does gener- 

 ally before the Lochy, up go all the fish that have been bred 

 in the Loch. 



