station of the Fish and Wildlife 

 Service contribute an aveia<»-e of 

 14.5 percent of the catch of tlie net 

 fisliery alone. Preliminary data in- 

 dicate the ini])()rtaiu'e of the salmon 

 from this hatchery in the offshore 

 troll fisliery northward from the 

 Sacramento Rivei' to Vancouver Is- 

 land, Caiuula. 



These and other hatchery opera- 

 tions have been successful in par- 

 tially compensatino- for the salmon 



losses caused by water-use projects. 

 At many localities the direct and 

 economical contributions of hatch- 

 eries to the salmon fisheries can be 

 demonstrated. It is not inconceiv- 

 able that hatchery propagation 

 alone can maintain a salmon fishery 

 of some magnitude in the event that 

 conditions preclude natural repro- 

 duction and if the requirements for 

 successful hatchery operations are 

 available. 



THE SALMON HATCHERY 



Hatchery propagation of salmon 

 is not recommended as a substitute 

 for natural propagation but may 

 be necessary to maintain salmon 

 population under certain circum- 

 stances. The construction of a 

 salmon hatchery is justifiable where 

 there is a particular need. 



A successful installation requires 

 an appropriate site and adequate 

 water of suitable quality and tem- 

 perature. Plans for a hatchery 

 must take into consideration the 

 numbers and species of salmon to 

 be produced, and the sizes of fish 

 to be released. These factors will 

 determine the rearing space re- 

 quired, the number of troughs or 

 other facilities needed to incubate 

 the eggs, and the quantity of fish 

 food to be stored, prepared, and fed. 



Hatchery Water Supply 



Most important for the success of 

 a salmon hatchery is the water sup- 

 ply in which the eggs are incubated 

 and the young fish reared. The sup- 

 ply must be adequate in volume. 

 Each hatchery trough may require 

 5 g. p. m. (gallons per minute) or 



more ; a rearing pond should receive 

 from 50 to 400 g. p. m., the amount 

 depending upon pond size and the 

 numbei-s of fish, as well as water 

 temperature and oxygen content. 

 A typical hatchery of 150 troughs 

 and 20 raceways, using water only 

 once through each trough or pond, 

 should have available not less than 

 7,000 g. p. m. or about 14 cubic feet 

 per second. If there are adult hold- 

 ing ponds, these can receive the 

 water from the ponds. Under 

 crow^ded conditions, when the num- 

 bers of adults approach the maxi- 

 mum capacity of the ponds, an ad- 

 ditional supply of fresh, well- 

 aerated water should be introduced. 

 The water to be used for salmon, 

 and trout, propagation must be of a 

 temperature within a definite range, 

 should be relatively free of silt and 

 debris, must be unpolluted, and 

 should not contain excessive quan- 

 tities of dissolved gases such as 

 nitrogen or of minerals such as cop- 

 per and iron. Within the range of 

 the Pacific salmon, hard water 

 rarely is encountered; most of the 

 coastal streams in which salmon are 



39 



