They don't start reproducing until they are more than 20 years old. De Vore said it takes about two years for the fish to spawn and spawning takes place once probably every three years. Unlike salmon, Sturgeon spawn in the main stem of the Columbia River and they require clean free-flowing water to spawn successfully. Researchers found a significant effect from the isolation of the dams. By counting the young of the year in the pools above the Columbia and Snake river dams and comparing that to the productivity of the lower river where the fish can freely migrate out into the ocean, the lower river was found to be much more productive, De Vore said.
Researchers estimate one million fish over two feet in length or larger on the lower Columbia.
Above the John Day, Bonneville and The Dalles dams the population was estimated to be only 50,000 in each reservoir. However that is an improvement in recent years. New fishing restrictions since the 1980s and two good years of river flows have helped recruitment in the reservoirs. Movement past dams was a rare event, and the fish moved mostly down stream. While fish ladders were built into the dams for salmon, salmon swim near the surface of the water and the ladders are built to accommodate them.