46 



THE MIGRATION AND CONSERVATION OF SALMON 



gram must be the determination of the ex- 

 tent to which the species to be conserved is 

 broken up into local populations. The de- 

 fining of specific populations is concerned to 

 a considerable extent with the determination 

 of the geographical limits occupied by each. 

 This is relatively simple in the case of plants 

 and of other fixed or non-migratory organ- 

 isms but may prove to be a problem of great 

 intricacy in the case of migratory animals 

 especially such animals as fish which cannot 

 readily be observed directly. Proof of the 

 existence of local populations of migratory 

 species does not, however, depend necessa- 

 rily upon a knowledge of the extent, direc- 

 tion and duration of the migrations in 

 question; adequate proof may be given by 

 entirely different evidence. 



A knowledge of the extent, direction and 

 duration of the migrations is, however, es- 

 sential to the determination and understand- 

 ing of the events and forces that affect the 

 birth-death ratio and, therefore, to a sound 

 conservation program. As specific examples 

 the fact that Columbia River Chinook 

 salmon are to be found off the coasts of 

 southeastern Alaska and British Columbia 

 during their oceanic migrations is of the 

 greatest importance to an understanding of 

 the causes affecting the abundance of these 

 fish. It is of importance because, in these 

 northern waters, the fish are subjected to an 

 intensive fishery carried on by hook and line 

 in the ocean and the development of this 

 fishery has undoubtedly increased the rate 

 of mortality although a measure of the effect 

 has not, and perhaps cannot be secured. 



Similarly the fact that the red-salmon 

 fishery in the Ikatan-Shumagin Islands dis- 

 trict south of the Alaska Peninsula draws 

 almost exclusively upon the runs to Bristol 

 Bay is important to an understanding of the 

 forces affecting abundance and to the out- 

 lining of effective conservation measures. 



Only through a knowledge of the migra- 

 tions of these fish could we know the drain 

 that such distant fisheries make on the par- 

 ticular runs. 



In general it is obviously important to dis- 

 cover causes of fluctuations in the birth- 

 death ratio. Such causes and their influence 



on the population may be exceedingly diffi- 

 cult to determine and measure under the 

 best of circumstances, but it is certainly im- 

 possible without a knowledge of the move- 

 ments of migratory animals such as the 

 salmon. 



There has been some confusion of these 

 two problems—that is to say, the problem 

 of the existence of local populations and the 

 problem of the nature of the migrations. 

 This is perhaps due to the fact that informa- 

 tion on both is so essential to practical con- 

 servation and because any complete study of 

 migrations must be preceded or accompanied 

 by a determination of whether local popu- 

 lations exist or not. But in our considera- 

 tion of the problems relating to the migra- 

 tions and conservation of salmon it is im- 

 portant that we keep clearly in mind the 

 distinction between the two. A knowledge 

 of both is important to sound conservation, 

 but there is this distinction : While, as I have 

 already pointed out, the demonstration of 

 the existence of distinct populations does 

 not depend on a knowledge of the migra- 

 tions, a study of the movements of fish re- 

 quires a knowledge of the population groups 

 to which the fish belong. 



Turning now to a consideration of the 

 salmon of the Pacific states and Alaska, I 

 shall take up first the evidence relating to 

 the existence of local populations and then 

 that bearing on the nature of the movements 

 of certain of these populations. 



Evidence of the existence of local popu- 

 lations of Pacific salmon may be considered 

 under three heads: (1) morphological and 

 chemical, (2) statistical and (3) experi- 

 mental. 



1. A list of demonstrated morphological 

 and chemical differences between fish run- 

 ning into different streams would be long 

 and varied. It can only be stated here that 

 there have been shown to be constant dif- 

 ferences in size, both with and without dif- 

 ferences in age ; significant differences have 

 been observed in the size of the mature eggs ; 

 differences in chemical composition espe- 

 cially as regards the oil content of the flesh 

 have been shown — differences that exist at 

 comparable stages of the spawning migra- 



