Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 7498
Title: Evidence for selective mortality in marine environments: the role of fish migration size, timing, and production type
Author: Andrew M. Claiborne, Jessica A. Miller, Laurie A. Weitkamp, David J. Teel, Robert L. Emmett
Publication Year: 2014
Journal: Marine Ecology Progress Series
Volume: 515
Pages: 187-202
Keywords: Chinook salmon,selective mortality,Columbia River Basin,Genetic stock identification,marine survival

The underlying causes of mortality during the critical life stages of fish are not well-understood, nor is it clear if these causes are similar for naturally and artificially propagated individuals. To assess the importance of selective mortality related to production type (hatchery vs. natural) and size at and timing of marine entry, we compared attributes of juvenile Chinook salmon (Oncorhynchus tshawytscha) from the upper Columbia River summer- and fall-run genetic stock group captured in the Columbia River estuary with back-calculated attributes of survivors captured later in marine waters. We used genetic stock identification, otolith chemistry and structure, and physical tags to determine stock of origin, size at and timing of marine entry, and production type. Fish emigrated from fresh water in May-September and the majority of fish collected in the estuary (83%) had arrived within 3 days of capture. In one of two years, timing of marine entry for both production types differed between the estuary and ocean: the ocean catch included a greater proportion of juveniles that emigrated in late July than the estuary catch. There was no evidence of selective mortality of smaller juveniles during early marine residence in hatchery or natural juveniles, but the mean percentage of hatchery fish in ocean collections was 16% (± 5.8 SE) less than in the estuary, which could indicate reduced survival of hatchery versus natural fish. Results from this study highlight the need to understand the effects of hatchery rearing and how hatchery-propagation may influence survival during later critical life-history transitions.

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Theme: Ecosystem approach to improve management of marine resources
Foci: Characterize ecological interactions (e.g. predation, competition, parasitism, disease, etc.) within and among species.
Understand how climate influences ecosystem variability.