Use of an Ecosystem‐Based Model to Evaluate Alternative Conservation Strategies for Juvenile Chinook Salmon in a Headwater Stream

Abstract

AbstractDeclining abundance of Chinook Salmon Oncorhynchus tshawytscha across the Pacific Northwest is an issue of great concern ecologically, culturally, and economically. Growth during the first summer is vitally important for juvenile Chinook Salmon, as it influences not only life history decisions (to smolt or not to smolt) but also subsequent river and ocean survival. Using Ecopath with Ecosim, we developed a food web model for a representative stream in the Salmon River basin, Idaho, to evaluate potential species‐specific and food web effects of three management strategies: (1) adding salmon carcasses or carcass analogs to promote primary production and detrital availability that were lost due to declining salmon returns; (2) removal of nonnative Brook Trout Salvelinus fontinalis, which are competitors with and predators on juvenile Chinook Salmon; and (3) stocking hatchery Chinook Salmon into streams to supplement wild production. Overall, juvenile Chinook Salmon responded strongly to increases in basal resources. Removal of Brook Trout had little effect on potential production for juvenile Chinook Salmon, but the responses of sculpins Cottus spp. were strong, primarily due to the sculpins’ high degree of dietary overlap with and predation by Brook Trout. Supplementation with hatchery‐origin juveniles depressed the production of wild juvenile Chinook Salmon, especially at the densities commonly applied to streams in this region. Our results suggest that efforts to enhance basal resources are likely to be the most effective in promoting the production of juvenile Chinook Salmon and nearly all food web groups considered in our model system. Removal of nonnative Brook Trout is unlikely to substantially affect salmon but could have a disproportionately large effect on nongame species, which are generally overlooked in single‐species management approaches.Received October 2, 2013; accepted March 24, 2014