A hidden-process model for estimating prespawn mortality using carcass survey data

North American Journal of Fisheries Management
By: , and 



After returning to spawning areas, adult Pacific salmon Oncorhynchus spp. often die without spawning successfully, which is commonly referred to as prespawn mortality. Prespawn mortality reduces reproductive success and can thereby hamper conservation, restoration, and reintroduction efforts. The primary source of information used to estimate prespawn mortality is collected through carcass surveys, but estimation can be difficult with these data due to imperfect detection and carcasses with unknown spawning status. To facilitate unbiased estimation of prespawn mortality and associated uncertainty, we developed a hidden-process mark–recovery model to estimate prespawn mortality rates from carcass survey data while accounting for imperfect detection and unknown spawning success. We then used the model to estimate prespawn mortality and identify potential associated factors for 3,352 adult spring Chinook Salmon O. tshawytscha that were transported above Foster Dam on the South Santiam River (Willamette River basin, Oregon) from 2009 to 2013. Estimated prespawn mortality was relatively low (≤13%) in most years (interannual mean = 28%) but was especially high (74%) in 2013. Variation in prespawn mortality estimates among outplanted groups of fish within each year was also very high, and some of this variation was explained by a trend toward lower prespawn mortality among fish that were outplanted later in the year. Numerous efforts are being made to monitor and, when possible, minimize prespawn mortality in salmon populations; this model can be used to provide unbiased estimates of spawning success that account for unknown fate and imperfect detection, which are common to carcass survey data.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A hidden-process model for estimating prespawn mortality using carcass survey data
Series title North American Journal of Fisheries Management
DOI 10.1080/02755947.2016.1245223
Volume 37
Issue 1
Year Published 2017
Language English
Publisher Taylor & Francis
Contributing office(s) Coop Res Unit Seattle
Description 14 p.
First page 162
Last page 175
Country United States
State Oregon
Other Geospatial South Santiam River
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