Life in the Fast Lane: Feeding and Growth of Juvenile Steelhead and Chinook Salmon in Main-Stem Habitats of the Columbia River Estuary

Very little is known about the ecology of juvenile Pacific salmon Oncorhynchus spp. that rapidly traverse estuaries. For these species and life history types, main-stem habitats are thought to largely function as migratory corridors rather than as productive habitats that support feeding or growth, although little research has focused on this issue. This is especially true in the highly modified Columbia River estuary, where it is unclear whether fast-migrating salmon benefit from extensive tidal marsh restoration. To address this deficit, we sampled migratory juvenile steelhead O. mykiss and Chinook Salmon O. tshawytscha at locations spread across nearly 200 km of the Columbia River estuary. Our results demonstrated that these juvenile salmon were actively feeding and growing as they moved downstream; dominant prey included chironomids, other insects, and corophiid and gammarid amphipods. We also observed variation in diet composition and quantity between years, which was likely associated with the highly contrasting river conditions. Insulin-like growth factor 1 hormone levels and the size of juvenile salmon increased as the fish moved downstream, suggesting that prey quality and quantity were sufficient to fuel rapid growth, which may increase survival in marine waters. Our results have direct management implications for habitat restoration and suggest the potential for competition between hatchery and wild salmon. Overall, our results support a fundamental shift in the view of main-channel estuarine habitats from serving primarily as a migration corridor to serving as productive habitat where rapidly moving salmon actively feed and grow.