predict that when all projected dams are installed on the 

 Snake River, juvenile chinook salmon from the Salmon River 

 will require 30 additional days to travel 415 miles to Bonne- 

 ville Dam, the last obstruction on the Columbia River before 

 the sea. 



FIGURE 32.— Biologists collect young salmon with a beach 

 seine. 



Timing and Rates of Migration 



Timing of migration of most juvenile salmon and steel- 

 head trout through free-flowing and impounded stretches 

 of the Snake and Columbia Rivers did not change appreciably 

 in 1966-68. Since 1965, young chinook salmon have migrated 

 from the upper Columbia River in July and August, but they 

 moved from the Snake River in the more normal time of 

 April-May. Sockeye and coho salmon and steelhead trout 

 from both streams also migrated in April and May. 



Our research revealed some variations in migration rates 

 of young chinook salmon. Generally, the rate was directly 

 related to water flows; the rate was 13 miles/day at low river 

 discharge and 23 miles/day during moderate river discharge. 

 Passage time through McNary and the newly formed John 

 Day Reservoirs was three times longer than through other 

 stretches of the Columbia and Snake Rivers. Our biologists 



Survival of Migrants 



The number of salmon and steelhead trout migrating 

 downstream in the Snake and Columbia Rivers varied in 

 recent years. The variations reflect differences in sizes of 

 runs of parent generations, in hatchery production, and in 

 survival in the rivers. 



The outmigration of juvenile chinook salmon from the 

 Snake River was 2i/4 million in 1968, the lowest since our 

 estimates started in 1964. By contrast steelhead trout, be- 

 cause of increased plantings of hatchery-reared fish in the 

 Salmon River in 1967-68, had an outmigration of nearly 

 4 million in 1968 — about 1 million more than 1967 and 

 21/2 million more than in 3 preceding years. 



From the upper Columbia River, migrations of sockeye 

 salmon declined abruptly from 4 million in 1966 to 1 million 

 in 1967; chinook salmon increased significantly. Populations 

 of coho salmon and steelhead trout remained nearly constant. 

 Most salmon and trout from the upper Columbia are now- 

 reared in hatcheries; changes in numbers of sockeye and 

 coho salmon outmigrants reflect the shift from rearing of 

 sockeye to coho salmon at Leavenworth Hatchery, Wash. 



The number of fish that survive to enter the ocean is not 

 known, l.)ut the total mortality is high. Survival of juvenile 

 chinook salmon between Ice Harbor Dam and The Dalles 

 Dam, a distance of about 150 miles, remained at about 50 

 percent in 1966-68. Highest mortalities (27 percent) were 

 near Ice Harbor Dam. By assessment of fish mortalities 

 along other stretches of the river and at dams, we hope to 

 learn why, where, and how great the losses are. 



25 — 



