Density Dependence and Its Implications for Hatchery Supplementation and Habitat Restoration Programs in the Columbia River Basin

This presentation highlights key findings regarding hatchery supplementation, habitat restoration and salmon recovery, based on the Independent Scientific Advisory Board’s (ISAB) 2015 report on density dependence in the Columbia River Basin: (1) Historical estimates of average all-species abundance in the Columbia Basin are likely over-estimated, but they are still much greater than today. (2) Density dependent responses are common in the Columbia Basin and appear sufficiently strong to constrain recovery of many ESA-listed populations, including those in pristine natal areas. (3) Hatchery spawners are intended to boost natural populations and may do so in some areas, but abundances on the spawning grounds often exceed current capacity, leading to unsustainable natural production and an inability to achieve an integrated hatchery approach—a key rebuilding strategy. (4) Hatchery spawners lower intrinsic productivity and also inhibit the natural rebound in productivity associated with lower density. (5) Culling surplus hatchery fish would increase population productivity, help achieve sustainability, and contribute to harvest goals. (6) The ISAB recommends balancing hatchery supplementation efforts with riverine capacity while implementing restoration actions that reduce limitations imposed by density dependence. The ISAB serves the Northwest Power and Conservation Council, NOAA Fisheries, and Columbia River Indian Tribes.