Previously Undocumented Two-Year Freshwater Residency of Juvenile Coho Salmon in Prairie Creek

• Main Authors: Ethan Bell, Walter G. Duffy
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Taft 1954; Bradford et al. 1997). In British Columbia; Arctic; Svenning; Atlantic salmon; Salmo salar; Salvelinus alpinus
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.534.6816; http://www.stillwatersci.com/resources/2007bellduffy.pdf

Abstract.—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. In addition to influencing freshwater and marine survival (Scrivener and Anderson 1984; Quinn and Peterson 1996), freshwater growth rates may affect timing of and age at smoltification in anadromous salmonids (Hogasen 1998). Økland et al. (1993) found that faster growing juvenile Atlantic salmon Salmo salar and brown trout S. trutta smolted at smaller sizes and younger ages than did their slower growing counterparts. Svenning et al. (1992) found that when food availability for Arctic char Salvelinus alpinus was low, growth rates were reduced and only a small fraction of the population reached the threshold size for smoltification. Increased summer growth rates of individual juvenile coho salmon in British Columbia were cited as an explanation for an observed increase in the proportion of juveniles smolting at age 1 instead of age 2 (Holtby 1988). Previous research in the southern portion of the species ’ range has not found evidence of coho salmon smoltification at age 2 ...