236 The Life Story of the Fish 



All fish tend to be attracted by lights at night. Downstream 

 migrant salmon, unlike the upstream spawners, travel mostly 

 at night. If a screen be placed in the mouth of a canal 

 diverting water out of a river, and lights move along its 

 face in the direction of the flow in the natural channel, the 

 little fish should follow in the same direction and get a start 

 on the proper path. This scheme has not yet progressed 

 beyond the experimental stage j whether it will be a real 

 contribution to the preservation of the salmon remains to be 

 determined. 



It must not be thought that all dams are harmful to all 

 fish in all ways. Where no anadromous species are involved 

 the effects may be largely beneficial. Even to the salmon 

 benefits have accrued in some cases, as at the Shasta Dam 

 on the Sacramento River. Before the dam was built none of 

 them spawned below its present site because the section was 

 too warm; they merely passed through it on their way to 

 more suitable areas further up. Now, chill waters from 

 the depths of Shasta Reservoir flow through the channel 

 below and have turned it into an excellent spawning area 

 where many salmon breed successfully. However, the bene- 

 fit here is no more than an offset to some of the damage 

 caused by the dam; it is too high for a fish ladder, and it cuts 

 the fish off from the spawning-beds above it which they used 

 to use. Furthermore, when the project is in full operation 

 the reservoir surface will in dry years be very near the bot- 

 tom, and there will be no cool depths from which to draw 

 water. 



Why is there this struggle to preserve the salmon's spawn- 

 ing-beds when it is so easy to strip eggs from ripe females, 

 fertilize them with milt from the males, and produce little 

 salmon in hatcheries? The answer is that while it is easy in 

 theory and with small numbers, it is not easy in practice and 

 with large numbers. When they first enter fresh water the 



