Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8139
Title: Using redd attributes, fry density, and otolith microchemistry to distinguish the presence of steelhead and rainbow trout in the Elwha River Dam removal project
Author: John R. McMillan, G. R. Pess, Martin Liermann, S. A. Morley, M. McHenry, Lance A. Campbell, T. P. Quinn
Publication Year: 2015
Journal: North American Journal of Fisheries Management
Volume: 35
Issue: 5
Pages: 1019-1033
Keywords: steelhead, rainbow trout, habitat features, recolonization, dam removal, salmon monitoring,
Abstract:

The removal of impassable dams can affect stream ecosystems in many ways, including allowing intermixing of life history variants within a single species.  The recolonization of anadromous forms into areas previously occupied solely by residents presents a challenge for monitoring recolonization because it may be difficult to directly observe staging or spawning adults, and the offspring of the forms are often outwardly indistinguishable during early life.  We evaluated the utility of redd (nest) attributes, fry (age 0) size and fry density to distinguish the presence of larger anadromous (steelhead) and smaller resident (rainbow trout) forms of Oncorhynchus mykiss in the Elwha River, Washington.  Redd area and gravel size (D50) successfully discriminated between forms:  steelhead redds had significantly larger surface area and had a greater D50 than rainbow trout redds.  Fry density was more than twice as high in the steelhead spawning reaches compared to rainbow trout reaches in two years, though significantly so in only one year.  In contrast, while fry were slightly longer in steelhead spawning areas compared to areas used by rainbow trout, there was no significant difference.  Otolith microchemical analyses revealed that steelhead fry during recolonization were intermediate in size to those found in steelhead and rainbow trout spawning areas prior to dam removal.  Thus, fry size may not effectively differentiate parental origin, despite the tendency of anadromous parents to be larger and spawn earlier than residents.  Redd attributes and fry density may be useful for evaluating the spatial distribution and relative abundance of steelhead and rainbow trout following dam removal, which has implications for other dam removal projects and species. 

URL1: The next link will exit from NWFSC web site http://dx.doi.org/10.1080/02755947.2015.1074965
Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.
Develop effective and efficient habitat restoration and conservation techniques.