Warmer water in the fall and cooler water in the spring delays adult spawning in the fall and juvenile emergence in the spring. Outflows from Brownlee Dam that would more closely approximate historical temperatures could affect this timing and improve survival. Higher flow may result in better survival downstream from the hydropower system, such as in the estuary. Flow management is providing benefits to smolt survival, but they are difficult to quantify. Impoundments create delays in travel time which flow management cannot entirely correct.
Downstream migrants continue to suffer high mortality.
Therefore, additional flow augmentation to benefit Snake River fall chinook would increase the likelihood of survival. Over 90 percent of transported fish are barged. One test of yearling chinook on the Snake River found that trucked fish return 5.8 times better than in-river, while barged fish return at a rate 8.9 times more, but the researcher suggested more tests should be done because another study of steelhead and fall chinook showed no significant difference. The potential for delayed transport mortality will require further study. In-river juvenile hatchery chinook migrate faster than barged hatchery fish, and they travel in tighter groups.