Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9060
Title: A network model for primary production highlights linkages between riverine fish populations and autochthonous resources
Author: W. Carl Saunders, Nicolaas Bouwes, Pete A. McHugh, Chris E. Jordan
Publication Year: In press
Journal: Ecosphere
Keywords: Gross primary productivity,autochthonous input,Stream habitat,

Spatial variation in fish densities across river networks suggests that the influence of food and habitat resources on assemblages varies greatly throughout watersheds.  Conceptual models predict that in situ primary production should vary with river characteristics, but the influence of autochthonous resource availability on the capacity for river reaches to support fish is poorly understood.  We estimated primary production throughout the South Fork and Middle Fork of the John Day River, Oregon, by measuring diel cycles in dissolved oxygen (DO) during July 2013.  Using these data, we 1) evaluated the extent to which juvenile salmonid abundance and resource limitation correlated with areas of high gross primary production (GPP), 2) developed models to predict GPP from both site-level measurements and remotely sensed data, 3) made predictions of GPP across the entirety if the Middle Fork John Day (MFJD) river network and assessed the utility of these spatially continuous predictions for describing variation fish densities at broad scales.  We produced reliable estimates of GPP at sites where DO loggers were deployed using measurements of solar exposure, water temperature, and conductivity measured at each site, as well as surrogates for these data estimated from remote sensing data sources.  Estimates of GPP across fish sampling sites explained, on average, 55% of the variation in juvenile salmonid densities during the summer sampling period, and 84% during the fall sampling period, while continuous network predictions of GPP explained 44% of variation in fish densities across 29 km of the MFJD.   Further, GPP explained nearly half of the variation in juvenile steelhead dietary resource limitation, as inferred bioenergetics modeling results.  These results comprise a first effort at quantifying variation in autochthonous production across an entire river network and, importantly provide a much-needed food web context for guiding more effective fish and habitat management.

Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.
Develop effective and efficient habitat restoration and conservation techniques.