Science Daily –
The survival and eventual return of juvenile Snake River salmon and steelhead to spawning streams as adults depends more on their size than the way they pass through hydroelectric dams on their migration to the ocean, new research shows.
Bypass systems are designed to carry juvenile salmon and steelhead around dam turbines on the Columbia and Snake rivers. The study found little evidence fish that go through these systems suffer delayed or “latent” mortality once they reach the estuary and ocean. Rather, they survive at about the same rate as fish that go through spillways and turbines.
The finding raises questions about whether spilling additional water past dams to carry more fish through spillways instead of bypass systems will substantially increase their survival in the ocean and the number that return to rivers as adults.
The new research helps address a call from the Northwest Power and Conservation Council’s Independent Scientific Advisory Board (ISAB) for further study of latent mortality. One argument for breaching dams on the lower Snake River is that it would improve fish survival by eliminating latent mortality related to bypass systems.