According to the Bonneville Power Administration (BPA), “Historic Columbia River Basin salmon returns, estimated anywhere between 5 to 16 million per year, declined long before the first federal dam (Bonneville) was built in 1938.” A graph prepared by BPA (
The Whole Dam Story) shows estimated historic fish numbers at less than 1 million annually in the years immediately preceding the building of Bonneville Dam.
What led to the decline in fish returns before the first dam was built? According to BPA “The new settlers took advantage of the abundance of natural resources to establish fishing, mining, logging, trapping, agriculture and other new industries. These industries had a huge impact on salmon and steelhead populations.”
Salmon were fished so heavily without a scientific understanding of their lifecycle or reproduction that leaders of the salmon fishing industry were very worried that salmon would become extinct, long before any Columbia or Snake dams were built.
In 1893, well before any dams were built, R.D. Hume wrote Salmon of the Pacific Coast "to call the attention of both producer and consumer to the danger of the total extinction of this most valuable of food fishes (salmon)..." Hume knew what he was talking about because he grew up on the east coast, in a fishing family, but had never tasted the native Atlantic salmon. When he was a boy, the native Atlantic salmon had already been so heavily overfished that they had become the rare delicacy of the rich men.
In the years after building the dams, salmon runs continued to decline. In response, BPA spent billions of dollars (and continues to spend) to make dam operations more fish-friendly. In addition to the improvements made to the dams, money has been spent on predator removal, habitat restoration, hatchery operations, and harvest management.
In 2014, BPA reported record salmon returns at 2.4 million since counts officially began at Bonneville Dam in 1938. While returns fluctuate each year, largely due to ocean conditions, the 10 year average trendline is up significantly when hatchery fish are included as compared to estimated returns immediately preceding the building of Bonneville. Please check out the
BPA chart that shows the numbers.