CHAP. v.J THE DOUBLE MIGRATION OF SALMON. 193 



It is supposed by some writers that the salmon makes 

 two voyages in each year to the sea, and this is quite pos- 

 sible, as we may judge from the data already given on this 

 point ; but sometimes the salmon, although it can swim with 

 great rapidity, takes many weeks to accomplish its journey 

 because of the state of the river. If there is not sufficient 

 water to flood the.course, the fish have to remain in the various 

 pools they may reach till the state of the water admits of their 

 proceeding on their journey either to or from the sea. The 

 salmon, like all other fish, is faithful to its old haunts ; and it 

 is known, in cases where more than one salmon-stream falls 

 into the same firth, that the fish of one stream will not enter 

 another, and where the stream has various tributaries suitable 

 for breeding purposes, the fish breeding in a particular tribu- 

 tary invariably return to it. 



But, in reference to the idea of a double visit to the salt 

 water, may we not ask particularly as we have the dates of 

 the marked fish for our guidance what a salmon that is 

 known to be only five weeks away on its sea visit does with 

 itself the rest of the year ? A salmon, for instance, spawning 

 about " the den of Airlie," on the Isla, some way beyond Perth, 

 has not to make a very long journey before it reaches the salt 

 water, and travelling at a rapid rate would soon accomplish 

 it ; but supposing the fish took forty days for its passage there 

 and back, and allowing a period of six weeks for spawning 

 and rest, there are still many months of its annual life un- 

 accounted for. It cannot, according to the ideas of some 

 writers, remain in the river forty-seven weeks, because it would 

 become so low in condition from the want of a proper supply 

 of nourishing food that it would die. It is this fact that has 

 led to the supposition of a double journey to the sea. The 

 Rev. Dugald Williamson, who wrote a pamphlet on this subject, 

 entertains no doubt about the double journey. "Salmon 

 migrate twice in the course of the year, and the instinct which 



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