62 



THE MIGRATION AND CONSERVATION OF SALMON 



controlled situation as is Cultus Lake. Then 

 notice that almost five times as many un- 

 marked fish returned as marked fish, viz., 

 3,930 to 804; in percentages nearly three 

 times as many, 0.88 per cent of the marked 

 fish that v^^ent out as young to 2.49 per cent 

 of the unmarked young. One may fairly 

 ask by what method one is justified in desig- 

 nating the conduct of the large majority as 

 "straying?" Is not the evidence really 

 unfavorable to the view that the movement 

 was due to a "homing instinct" and more 

 naturally related to the view that the migra- 

 tion of the fish is controlled by environmental 

 conditions which in some cases are such as 

 to bring them back to the place in which 

 they began life and in other cases not? It 

 does not seem necessary to consider here a 

 possible third view that the movements are 

 subject to mere chance. 



In further analysis of the situation I pro- 

 pose to accept the compromise that return 

 to the parent stream may be the rule and to 

 test if possible the extent to which that as- 

 sumed response is due to some blind instinct 

 or should be more probably the result of 

 environmental control. 



Whether the departure from the assumed 

 rule be 10 per cent or 25 per cent or more 

 awaits determination by further accurate 

 studies. The fact that some fish do go 

 astray is important and the degree to which 

 migration is modified is even more so since 

 it is the means by which other runs are 

 strengthened or new runs are established. 

 Very likely it was the method by which 

 originally the species was dispersed. The 

 conditions under which scattering occurs 

 and the factors which direct or limit it are 

 consequently significant. 



In the next place, lakes and rivers are not 

 static habitats ; changes in stream conditions 

 are often brought about by natural influences 

 and more conspicuously by human inter- 

 ference. When forests are lumbered oif or 

 burnt off, temperature levels are modified, 

 stream flow becomes more variable, amount 

 and type of food are altered and thus con- 

 ditions may become unfavorable at times of 

 migration or spawning. As these difficulties 

 arise it is essential to have some under- 



standing of the environmental factors that 

 modify behavior. Only through such knowl- 

 edge is it possible to determine the cause of 

 fluctuations in the run, to distinguish be- 

 tween periodic and permanent changes in 

 numbers or to provide for the conservation 

 of the species. Man must seek to add to 

 favorable conditions as well as to correct or 

 limit unfavorable changes. An old resident 

 of Seattle who was a careful, trustworthy 

 observer and had had long and intimate con- 

 tact with the Puget Sound region told me 

 that in the early days every small stream 

 along the shore north of Seattle was crowded 

 at spawning time with some kind of salmon. 

 Yet we know that now many of these 

 streams, highly altered, carry no salmon. 

 Are we to consider that each of these streams 

 sheltered a population group that was wiped 

 out, and can each be replanted and develop 

 a new run, or are conditions changed so 

 that they no longer "attract" salmon? 

 Only experimentation will decide such ques- 

 tions and certain it is that planting has 

 failed in many cases to establish new runs 

 in some of these streams. 



In numerous lakes both in America and 

 in Europe are found landlocked races of dif- 

 ferent salmon. Their close relationship to 

 sea-run species is generally recognized. In 

 another paper (Ward, 1932) I have dis- 

 cussed these groups and have shown that 

 they are not shut off from the sea by impass- 

 able material barriers, but that they are 

 probably held back from migrating to salt 

 water by temperature conditions which limit 

 their movements. This view is supported 

 by the discovery of a newly formed race 

 which was cut off from its former pathway 

 by temperature changes incident to the 

 building of a high dam and the consequent 

 formation of a stratum of warm water in the 

 course of a cold rivei*. Such changes in en- 

 vironmental conditions certainly can alter 

 and have altered the original relations of the 

 salmon to the stream. In this manner origi- 

 nated a landlocked group which was 

 restrained by a permanent change in temper- 

 ature conditions. Furthermore the tempera- 

 ture may affect variably young sockeyes at 

 different ages and, in connection possibly 



