years, the inflow and outflow have 

 been placed at opposite ends of the 

 pond, eliminating dead-water areas 

 to some extent. 



Of the many types of rearing 

 ponds in use, the raceway pond is 

 believed best suited to mass produc- 

 tion of salmon fingerlings. Its 

 capacity, measured in production 

 per cubic foot of water, or per gal- 

 lon per minute, probably is not so 

 great as the circular pond; but its 

 disease-inhibiting characteristics, 

 as well as ease of cleaning, feeding, 

 and handling the fish make it desir- 

 able where ample water supplies are 

 available. 



Trapping Adult Salmon 



The location of traps for the tak- 

 ing of adult salmon for spawning 

 will depend upon the species of fish 

 sought. The most desirable trap- 

 ping locality is immediately below 

 the natural spawning area, where 

 the fish can be taken when fully ma- 

 ture, but this usually is not feasible. 

 The trapping for spawning of 

 spring chinook, silver salmon, and 

 steelhead trout offers the greatest 

 difficulties, for many adults of these 

 species may need to be held for 

 weeks or months before spawning. 



Until recent years it had been 

 the general practice to place racks 

 or weirs across a stream at a suitable 

 point to enclose an area within 

 which the adult salmon were 

 trapped for spawning. The lower 

 rack was so constructed as to permit 

 the upstream passage of fish 

 through one or more V-openings 

 which could not easily be found 

 again for escape. The upper rack 

 permitted no passage. The mature 



fish were seined from the area and 

 fipawned. Several variations of this 

 type of rack are sketched and de- 

 scribed by O'Malley (1920). 



Although the trapping and 

 spawning of some species of salmon 

 in the stream continue to be neces- 

 sary where circumstances permit, a 

 general practice is to install a di- 

 version rack or dam in the stream 

 and thus to divert the adult fish into 

 a side channel or up a fish ladder 

 :and thence into concrete or earthen 

 holding and spawning ponds. 



A rack placed across a stream con- 

 sists of weighted wood or steel tri- 

 pods between which stringers are 

 extended. Sections of suitably in- 

 terspaced strips laid vertically are 

 placed or leaned against the string- 

 ers on the upstream side of the tri- 

 pods. The interspaces in the rack 

 are of such width and number as 

 to permit the free flow of water 

 through the rack but are sufficiently 

 small or narrow to deny passage of 

 the salmon. The rack must be fish- 

 tight along the stream bottom. 

 O'Malley (1920) gives a detailed 

 description of rack construction. 



The streamflow characteristics, as 

 well as the size and quantity of 

 debris, such as logs, brush, and 

 leaves, must be considered when de- 

 termining the size and strength of 

 the rack. The largest salmon rack 

 ever attempted was laid across the 

 main Sacramento River. The steel 

 tripods were 12 feet high, and each 

 of these weighed many tons when 

 loaded with rock (on a platform 

 within the three legs) to hold posi- 

 tion in the cuireut. The racks were 

 of steel or strap iron. Flash floods 

 in the river frequently shifted or 



48 



