Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8837
Title: Roads to ruin: conservation threats to a sentinel species across an urban gradient
Author: Blake E. Feist, E. Buhle, D. H. Baldwin, J. A. Spromberg, Steve Damm, J. W. Davis, N. L. Scholz
Publication Year: 2017
Journal: Ecological Applications
DOI: 10.1002/eap.1615

Urbanization poses a global challenge to species conservation.  This is primarily understood in terms of physical habitat loss, as agricultural and forested lands are replaced with urban infrastructure.  However, aquatic habitats are also chemically degraded by urban development, often in the form of toxic stormwater runoff.  Here we assess threats of urbanization to coho salmon throughout developed areas of the Puget Sound Basin in Washington State, USA.  Puget Sound coho are a sentinel species for freshwater communities and also a species of concern under the U.S. Endangered Species Act.  Previous studies have demonstrated that stormwater runoff is unusually lethal to adult coho that return to spawn each year in urban watersheds.  To further explore the relationship between land use and recurrent coho die-offs, we measured mortality rates in field surveys of 51 spawning sites across an urban gradient.  We then used spatial analyses to measure landscape attributes (land use and land cover, human population density, roadways, traffic intensity, etc.) and climatic variables (annual summer and fall precipitation) associated with each site.  Structural equation modeling revealed a latent urbanization gradient that was associated with road density and traffic intensity, among other variables, and positively related to coho mortality.  Across years within sites, mortality increased with summer and fall precipitation, but the effect of rainfall was strongest in the least developed areas and was essentially neutral in the most urbanized streams.  We used the best-supported structural equation model to generate a predictive mortality risk map for the entire Puget Sound Basin.  This map indicates an ongoing and widespread loss of spawners across much of the Puget Sound population segment, particularly within the major regional north-south corridor for transportation and development.  Our findings identify current and future urbanization-related threats to wild coho, and show where green infrastructure and similar clean water strategies could prove most useful for promoting species conservation and recovery.

Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.
Characterize the interaction of human use and habitat distribution, quantity and quality.