Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 1443
Title: Diminished reproductive success of steelhead from a hatchery supplementation program (Little Sheep Creek, Imnaha Basin, Oregon)
Author: E. A. Berntson, R. W. Carmichael, Michael W. Flesher, E. J. Ward, Paul Moran
Publication Year: 2011
Journal: Transactions of the American Fisheries Society
Keywords: salmon, reproductive success, selection gradients, microsatellite, hatchery/natural interation
Abstract: Hatchery supplementation programs are designed to enhance natural production and maintain fitness of the target population; however, it can be difficult to evaluate the success of these programs. Key to the success of supplementation programs is relatively high reproductive success of hatchery fish compared to the natural fish. This study investigated relative reproductive success (RRS) of steelhead by creating pedigrees for hatchery and natural spawning steelhead. We genotyped adult steelhead (Oncorhynchus mykiss) that returned to a weir and were released upstream to spawn in Little Sheep Creek, a tributary to the Imnaha River in eastern Oregon. Broodstock for this supplementation program were originally chosen from natural origin steelhead returning to the weir, and in subsequent years consisted of both natural and hatchery origin individuals. Results of the microsatellite analyses showed the broodstock to be genetically similar to the natural population across years. We also genotyped adult resident rainbow trout from multiple locations upstream of the weir, and determined the parentage of progeny collected at various life history stages, including returning adults in subsequent years. Results from analysis of progeny sampled at both the juvenile and adult life stages suggested that RRS of hatchery origin fish was 30-60% that of their natural origin counterparts. Using generalized linear models to address the importance of various factors associated with reduced reproductive success, we found that the greatest effects on RRS were origin (natural vs. hatchery), length, return date, and the number of same-sex competitors. Natural parents were less negatively affected by same-sex competitors. Differential survival of juveniles and behavior of offspring and/or spawning adults may all contribute to diminished fitness in hatchery-reared salmon, although it could not be determined to what extent these effects were of a persistent heritable nature versus an environmental effect associated with hatchery rearing and release strategies.