Hatchery propagation did not reduce natural steelhead productivity relative to habitat conditions and predation in a mid-Columbia River subbasin

Abstract

For over 150 years, hatchery-origin anadromous salmon and trout have been reared and released throughout the Pacific Northwest to mitigate for lost habitat and sustain harvest opportunity. Some studies demonstrate that introgression of hatchery and naturally produced fish may constrain conservation efforts through maladaptive genetic processes. However, empirical demonstrations of the influence of these genetic interactions on population productivity are lacking, making it difficult to assess their importance relative to other drivers of productivity. We estimated the effect of the proportion of hatchery-origin spawners (pHOS), proportionate natural influence (PNI), and hatchery fish releases on natural adult winter steelhead recruitment in the Hood River, Oregon, over a 27-year period of record. Adult winter steelhead productivity was not associated with pHOS and PNI. However, natural winter steelhead productivity was positively associated with ocean conditions, stream flow, and hatchery fish release numbers, while negatively associated with pinniped abundance. Our analysis highlights the importance of quantifying the influence of hatchery programs on fish production relative to environmental factors known to affect natural-origin anadromous fish recruitment.