Do network relationships matter? Comparing network and instream habitat variables to explain densities of juvenile coho salmon (Oncorhynchus kisutch) in mid‐coastal Oregon, USA

Abstract

ABSTRACT Aquatic ecologists are working to develop theory and techniques for analysis of dynamic stream processes and communities of organisms. Such work is critical for the development of conservation plans that are relevant at the scale of entire ecosystems. The stream network is the foundation upon which stream systems are organized. Natural and human disturbances in streams alter the configuration of stream habitats such as pools, riffles, and glides across seasons, decades, or centuries. Thus, native aquatic species have developed mechanisms for adapting to the dynamic configuration of habitats in stream networks. At different spatial scales, stream network structure informs habitat connectivity for aquatic–obligate species. The movement of aquatic species both upstream and downstream is limited by stream channels and may be modified by the downstream flow of water, nutrients, and physical materials such as wood and substrate. Analysing streams as networks offers a realistic and holistic perspective for assessing movement and distribution by freshwater aquatic species in response to life‐history needs and environmental conditions. In this study, network analysis was facilitated by automating, in a Geographic Information System, the calculation of network distances and variables that represent spatial configuration. A comparison between traditional instream habitat variables and network variables for juvenile coho salmon (Oncorhynchus kisutch) in seven sub‐basins of Oregon's mid‐coast over a 5‐year period revealed that network variables perform better at explaining juvenile coho salmon density than instream habitat variables. Moreover, analysis of network distances among seasonal habitats indicates that juvenile coho salmon density may be higher where the distance between critical seasonal habitats is short. This work furthers aquatic conservation, management, and restoration by including analysis of the proximity and connectivity among aquatic freshwater habitats. Published in 2012. This article is a US Government work and is in the public domain in the USA.