Migration 



beneath the sea ; this may account for the many birds 

 which cross the North Sea to this country and then pass 

 due south across the Channel. 



Migration amongst fishes is of quite common occur- 

 rence, though the subject, in general, is of too abstruse a 

 character to deal with in these pages. A certain South 

 American fish, equally at home on land or in water, 

 travels rapidly overland by violently lashing its tail, 

 supporting itself the while on its breast fins. In this 

 manner it passes from one waterway to another. Occasion- 

 ally whole nights are occupied in the journey. Usually 

 these fishes travel singly or a few at a time ; sometimes, 

 however, they migrate in large bands. 



Well-authenticated cases of migration occur amongst 

 salmon and eels, therefore we will confine our remarks 

 to the wanderings of these two common fishes. The life 

 history of the salmon is interesting in the extreme ; part 

 of its existence is spent in fresh water, part in the sea. 

 During the summer and autumn there is a regular migra- 

 tion from the sea to the rivers. Spawning takes place in 

 fresh water. There the young grow into parr and smolt 

 before travelling back to the sea, where they become grilse 

 and salmon before returning to fresh water. After the 

 salmon have travelled up-stream to spawn, a journey 

 fraught with dangers and difficulties, which the fish use 

 every effort to surmount, they pair off and seek some 

 gravel-bed in a shallow part of the stream ; then by 

 violent lashing of their tails they form a hollow, in which 

 the eggs are laid and fertilised, and, by further tail- 

 lashings, are covered with gravel. The usual time for this 

 family event to take place is November and December, 

 but spawning may go on from September to January. 

 In addition to this so-called spawning migration, a 

 general seasonal migration of salmon takes place every 

 year. By marking the fish in their young stages some 

 interesting experiments have been carried out, which have 

 proved that the spawning salmon usually return to the 



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