Ward. — Migration of the Sockeye Salmon 421 



time comes. But in my opinion such a lake, if its utilization 

 is to be successful, should not be nearer the sea than the orig- 

 inal home of these red salmon fry, nor less abundantly sup- 

 plied with their proper food, nor unfavorably affected by 

 lack of protected areas, abundance of predatory fish, or tem- 

 perature changes towards which the fry react unfavorably. 

 Otherwise they may be destroyed or be stimulated to migrate 

 too easily, and Gilbert has shown that salmon entering the 

 sea prematurely must perish since they never return to spawn. 

 In case it is not feasible to install a hatchery and care for 

 the eggs of the salmon that have been held up below the dam, 

 then they certainly should be enabled in some way to pass this 

 obstruction since they cannot spawn naturally below it, and to 

 prevent their going up stream farther will inevitably result in 

 the destruction of the run. This was demonstrated on a grand 

 scale with the Atlantic salmon more than a century ago and no 

 further experiments are needed to establish the fact (Jordan 

 and Evermann, 1902:164). It must be confessed that under 

 the changed conditions the results are uncertain in any case. 

 The introduction of a new water body of large area in most 

 cases has modified natural conditions greatly. The fish will 

 not be directed by the same stimuli that controlled them before; 

 the current is greatly reduced or entirely lacking, and the tem- 

 perature certainly highly modified so that the behavior of the 

 salmon cannot be foretold. But when the new lake has not 

 covered the original spawning grounds, one may expect the 

 fish to reach them and to spawn naturally. In this case it will 

 be necessary to protect the outlet of the artificial lake and to 

 lift the young salmon over the dam when on their down- 

 stream migration they reach that point. But, as suggested 

 above, even this type of situation is fraught with uncertainties. 

 The impounding of a huge mass of water and the formation of 

 a great artificial lake has modified biological conditions fun- 

 damentally. The depth of the water, the current, the char- 

 acter of the bottom, type of materials in suspension and pos- 

 sibly also in solution, and the temperatures of the water at dif- 



