Assigning the causes of salmon mortality can only be estimated. Three time periods are of interest. One is what the resource might have been like at the time of European contact. The second is the status of the resource at construction of the first dams. Third is the current status of salmon.

Graphs show the human-caused, both fishing and nonfishing mortality and estimated natural mortality at each of these times. See the recommended readings for sources useful in constructing these graphs. The Oregon Department of Fish and Wildlife and Washington Department of Fish Wildlife annual Status Report is the basis for post 1938 estimates. The Chapman, Boyd, and Craig and Hacker references are useful for the 1770 estimate. This is a very general overview and the specifics of the salmon situation are very complex.

The amount of natural mortality circa 1990 might be a surprise. Keep in mind that the catches are only those in the Columbia River. Catches have been severely restricted to protect the remaining salmon. The estimate is for all salmon, which include strong runs into the Willamette and all salmon spawning below Bonneville Dam. Coho, for example, the second largest contributor, when counting the number of salmon, spawn mainly in the lower river and are predominantly a hatchery-based stock.

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