Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4749
Title: Analyzing large-scale conservation interventions with Bayesian hierarchical models: A case study of supplementing threatened Pacific salmon
Author: M. D. Scheuerell, E. Buhle, B. X. Semmens, Michael J. Ford, T. Cooney, R. W. Carmichael
Publication Year: 2015
Journal: Ecology and Evolution
Volume: 5
Issue: 10
Pages: 2115-2125
Keywords: salmon, hatchery, time series, BACI, hierarchical Bayesian models,

Myriad human activities increasingly threaten the existence of many species.  A variety of conservation interventions such as habitat restoration, protected areas, and captive breeding have been used to prevent extinctions.  Evaluating the effectiveness of these interventions requires appropriate statistical methods, given the quantity and quality of available data.  Historically, analysis of variance has been used with some form of predetermined before–after control–impact design to estimate the effects of large–scale experiments or conservation interventions.  However, ad hoc retrospective study designs or the presence of random effects at multiple scales may preclude the use of these tools.  We evaluated the effects of a large–scale supplementation program on the density of adult Chinook salmon Oncorhynchus tshawytscha from the Snake River basin in the northwestern United States currently listed under the U.S. Endangered Species Act.  We analyzed 43 years of data from 22  populations, accounting for random effects across time and space using a form of Bayesian hierarchical time–series model common in analyses of financial markets.  We found that varying degrees of supplementation over a period of 25 years increased the density of natural–origin adults, on average, by 0–8% relative to nonsupplementation years.  Thirty–nine of the 43 year effects were at least two times larger in magnitude than the mean supplementation effect, suggesting common environmental variables play a more important role in driving interannual variability in adult density.  Additional residual variation in density varied considerably across the region, but there was no systematic difference between supplemented and reference populations.  Our results demonstrate the power of hierarchical Bayesian models to detect the diffuse effects of management interventions and to quantitatively describe the variability of intervention success.  Nevertheless, our study could not address whether ecological factors (e.g., competition) were more important than genetic considerations (e.g., inbreeding depression) in determining the response to supplementation. 



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Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Describe the relationship among human activities and species stock status, recovery, rebuilding and sustainability.
Maximize effectiveness and minimize impacts of artificial propagation in recovery, rebuilding and stock sustainability