Chapter 19. Stream Restoration for Anadromous Salmonids by the Addition of Habitat and Nutrients

Summary

Abstract:

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• In an evaluation of the salmonid response to watershed rehabilitation treatments at the Keogh River, we document the positive trends in juvenile density, growth, survival and smolt yield of steelhead trout and coho salmon observed in comparison to the untreated neighbouring Waukwaas River, on northern Vancouver Island, British Columbia, Canada. Juvenile fish abundance in the Keogh River indicated positive effects of the increased watershed restoration, particularly that from the addition of habitat structures and nutrients. Steelhead parr densities in the Keogh River were significantly higher compared to untreated (both rivers) and pretreatment values, and highest in reaches treated with both restoration techniques. Despite reductions in adult escapement, the abundance of coho fry in the Keogh River exceeded that in the Waukwaas River; densities in preferred habitat exceeded those of past surveys. Inorganic nutrient addition led to significant increases in salmonid fry and smolt weights. Increase in length and weight of steelhead parr improved survival over winter, culminating in increased smolt yield and a shift to predominantly 2-year-old smolts in 1999, 2000 and 2001. Smolt yield reflected significant improvements in juvenile production and survival in the freshwater phase in the Keogh River despite low brood year strength, and proved the better response variable; juvenile density was highly variable. Steelhead smolt yield in 2001 was > 2000 smolts. Coho smolt yield increased in 2001 from the Keogh River, but less so than in 2000, over the historically poor yield observed in 1998. Steelhead smolts produced per spawner in the Keogh River have risen from historic lows of < 3 smolts per spawner (i.e. below replacement) from the 1996 brood to > 50 smolts per spawner from the 1998 brood year, the highest production per spawner of the 27-year record, offering hope for recovery despite low smolt-to-adult survivals. Further evaluation of effects to salmonid smolts will require a continued analysis of smolts-per-spawner recruitment to at least 2004, to more fully describe the benefits of the watershed ecosystem approach to restoration.