Experts debate impact of ocean conditions on salmon, steelhead survival

The Lewiston Tribune –

Many variables influence the survival of Snake River salmon and steelhead, but perhaps none more than the hospitality of the Pacific Ocean in any given year.

Juvenile salmon and steelhead that survive their downstream migration through the Snake and Columbia river hydrosystem must next survive from one to three years in the ocean, and the first few weeks to months is critical. When ocean conditions are good, the young fish find abundant food and grow more quickly, making them stronger and boosting their chances of survival. When conditions are poor, food is scarce and predators associated with warmer water can be abundant. This diminishes their chances of survival.

Some have postulated that the depressed state of Snake River salmon and steelhead can be traced almost entirely to ocean conditions. Under this view, the effect of the ocean is so powerful that it swamps all other factors. To support this theory, its proponents point to other river systems with fewer or no dams that have also seen salmon declines in recent years.

Others say it is impossible to separate ocean and freshwater conditions when measuring overall survival. This group doesn’t dispute that ocean conditions play a large role in salmon survival, but they say freshwater factors are also important. Many of them say that mortality related to dam and reservoir passage is present and significant in years with both good and poor ocean conditions.

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