FISHERY BULLETIN: VOL. 71, NO. 2 



Figure 1. — The Hanford environs of the free-flowing 

 Columbia River between Richland, Wash., and Priest 

 Rapids Dam. 



and protecting spawning and rearing areas 

 in available tributaries. The free-flowing Han- 

 ford section, however, still supports a sizable 

 spawning population of fall chinook salmon 

 that has produced an increase from about 

 300 redds in 1960 to about 4,500 redds in 

 1969 (Watson, 1970). The annual contribution 

 of seaward migrants from the Hanford popula- 

 tion to the combined natural production of 

 the Columbia and Snake Rivers is not known. 

 But the Hanford population has clearly ac- 

 quired considerable importance in sustaining 



natural salmonid runs within the Columbia 

 River Basin, 



ENVIRONMENTAL CONDITIONS 



River temperatures and discharges are two 

 factors potentially influencing the availability 

 of food organisms, feeding activity, and growth 

 of juvenile chinook salmon in the central 

 Columbia River. The ecological aspects of these 

 two factors are evaluated in the Discussion 

 of this report. 



The annual cycles of temperature and dis- 

 charge (Figure 2) are essentially similar from 

 year to year. Temperatures are lowest in 

 January and February when eggs of fall 

 chinook salmon are buried in the gravel, rise 

 during the spring as fry emerge, and peak 

 during August and September. From the stand- 

 point of known thermal requirements (Brett, 

 1952), temperatures are well below the thermal 

 preferendum of juvenile chinook salmon (12°- 

 14 °C) in March and April, enter the preferred 

 range in May and June — when conditions are 

 presumably optimum for feeding and growth, 

 and extend into the upper zone of thermal 

 tolerance during July and August. 



Temperatures at Priest Rapids Dam (above 

 Hanford) were somewhat lower than those 



-200 



- 150 



100 



50 



FEB. MARCH 



APRIL 



MAY 



AUG. 



SEPT. 



Figure 2. — Temperature and flow conditions in the central Columbia River during 

 the spring and summer of 1969, in relation to the presence and preferred temperatures 

 of juvenile fall chinook salmon. 



388 



