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Scientific Report

Iteroparity in Complex Mating Systems of Steelhead Oncorhynchus mykiss (Walbaum)



This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss. Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River = 7.5% and Salmon River = 9.4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18.2%), Imnaha River (17.4%), Pahrimeroi Hatchery (25.2%) and Asotin Creek (22.2%). A lack of correlation between population escapement size and kelt proportions (P > 0.05) suggests that iteroparity was not uniformly expressed acress populations, but was significantly negatively correlated with body size (P < 0.05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations.


Shawn R. Narum, Doug Hatch, Andrew Talbot, Paul Moran, and Madison Powell


Narum, S.R., D. Hatch, A. Talbot, P. Moran, and M. Powell. 2008. Iteroparity in Complex Mating Systems of Steelhead Oncorhynchus mykiss (Walbaum). Journal of Fish Biology 72:45-60.


Jul 9th, 2007

Report No.


Media Type

Journal Article

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