SALMON AND TROUT— SCHULTZ 367 



These species may be observed to build nests and perhaps spawn 

 by anyone who has the patience and time to study such activities. 

 The observer should cautiously approach the gravel riffles in which 

 saucerlilve depressions, 1 to 4 feet in diameter, have been excavated 

 and where trout occur during the spawning season. If he remains 

 very still, in 5 to 20 minutes the breeding salmon or trout will swim 

 back over the riffle where they were when the observer first made his 

 appearance. These fish may stay a moment, then leave for the deep 

 hole again, usually above the riffle, where they hide for some time 

 before again venturmg out. However, if all is still and quiet after 

 one or more such attempts, the spawning salmon or trout will remain on 

 the riffle, nearly oblivious of the presence of the spectator. If the 

 observer should make sudden movements they dart away, and then 

 he must wait for them to return and again become accustomed to his 

 presence. It is possible to become so much a part of the environment 

 that the observer **can even stand astride one of the nests, while the 

 male and female redfish pursue their normal activities" (Schultz and 

 Students, Mid-Pacific Magazine, January-March 1935, p. G9). 



The spawning salmon and trout usually segregate themselves in 

 pairs, although an extra male may be present in certain species 

 (rainbow) during the spawning act. Each of these pairs remains 

 over a certain area in the stream bottom which it defends. This area 

 becomes the nest, or redd, in which the eggs are laid. Since the 

 nest-buildmg activities are practically the same for all species of salmon 

 or trout, the following account of the activities of the little redfish, 

 the landlocked sockeye salmon, Oncorhynchus nerka, is given from 

 personal observations (pi. 1, fig. 1). 



NEST-BUILDING ACTIVITIES 



A pair of redfish usually engage in normal nest building when un- 

 molested by other fish. If the pair is alone, the female may let herself 

 drift over the lower center of the redd, where she will turn over on her 

 side and vigorously flex her tail four to six times against the bottom, 

 as this motion carries her a foot or more upstream. The tail of the 

 fish during these movements comes in contact with the bottom, and 

 vigorous hydraulic forces are set up by the upward movement of the 

 tail, which hft the gravel and sand off the bottom. The material thus 

 disturbed is carried by the swift current downstream, the smaller 

 particles farthest and the larger stones but a few inches before they 

 settle. The female may return to the starting point and repeat this 

 nest-building act (fig. 1). If undisturbed, she may in 20 minutes 

 complete as many as 70 separate nest-building acts with an interval 

 between them of as Uttle as 4 seconds or as long as IK minutes. On 

 the average, females turn, with almost equal frequency, either their 

 left or right side toward the stream bottom. 



