Over 2,000 juvenile coho salmon Oncorhynchus kisutch were tagged with passive integrated transponder (PIT) tags during the fall of 1998 and 1999 in Prairie Creek, California, as part of a study on individual winter growth rates and movement of juvenile coho salmon. During this study, age-2 out-migrants were incidentally observed. Previously, it had been generally assumed that all juvenile coho salmon in northern California streams spend only 1 year in freshwater before out-migrating at age 1 and that a 2-year freshwater life history pattern was found only in the more northerly portions of the species' range. Subsequently, scale analysis of PIT-tagged fish recaptured during spring out-migration was used as a basis for estimating the proportion of out-migrants displaying a 1- or 2-year freshwater residency life history. Twenty-eight percent (28%) of out-migrants captured in spring 2000 displayed a 2-year freshwater residency life history, apparently related to low winter growth rates documented in related research in the study stream. ?? Copyright by the American Fisheries Society 2007.
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Previously undocumented two-year freshwater residency of juvenile coho salmon in Prairie Creek, California