22 MUSEUM BULLETIN NO. 13. 



parr are supported by fry. How many fry it takes to raise a 

 parr to the smolt stage we cannot tell, but it must be an en- 

 ormous number. 



The shelldrakes (mergansers) are accused of devouring the 

 salmon ova. Considering that the ova is buried in the sand 

 immediately after being fertilized and is guarded by the male, 

 while this is in process, it is not likely that the number taken 

 by these birds can be a very large proportion of the whole and 

 must be small in comparison with the number of fry taken by the 

 parr. At this stage, the worst enemy of the salmon is un- 

 doubtedly the salmon itself. 



The parr, to the smolt stage, are thus obviously limited 

 in number by the amount of fry in the river. If it can be es- 

 tablished that the kelt or grilse eat in fresh water they are 

 probably the parr's worst enemy. If not, that distinction falls 

 to the lot of the kingfisher who undoubtedly consumes con- 

 siderable numbers of them. 



Whether they seriously reduce the final number that go 

 to the sea as smolt is a question of more than one aspect. A 

 reduction of parr means an increased number of fry and, there- 

 fore, more food for the remaining parr who being better fed may 

 be stronger and more fitted to survive later dangers. If the 

 birth rate is markedly greater than the food capacity of the 

 streams, kingfishers may have no harmful effect. They should 

 not be finally condemned until this point is investigated. 



The population of fry produced by the birth rate is 

 greater than can be raised and the surplus must necessarily 

 be reduced, if not by one agent, then by another. There is a 

 point to be reached when even an immense increase in the 

 number of fry introduced into the streams will be ineffective in 

 increasing the output of smolt. As the birth rate has been 

 evolved under present conditions of food supply and enemy 

 factors, the natural conclusion is, that the kingfisher and the 

 shelldrakes are compensated for in it. The natural increase 

 was sufficient to stock the river in the past to abundance, in 

 spite of these enemies, and there is no reason to suspect that it 

 is less effective now. Hence if man introduces sufficient fry to 

 compensate for the ova that should be laid by the breeding 



