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Effects of life history variation on size and growth in stream-dwelling Atlantic salmon
Authors:B. H. Letcher , G. Gries &dagger  
Affiliation:U.S. Geological Survey/Biological Resources Division, S.O. Conte Anadromous Fish Research Center, P. O. Box 796, One Migratory Way, Turners Falls, MA 01376, U.S.A.
Abstract:A large size variation amongst life histories for stream-dwelling Atlantic salmon Salmo salar was found and the relative effect of life histories on size varied over time. As early as December (age 0+ years), fish that later smolted at age 2+ years were significantly larger than fish that did not smolt at age 2+ years. In contrast, there were no mass differences at age 0+ years between fish that would mature or not at age 1+ years (October). The mass differences between smolts and non-smolts persisted until smolting, and differences between mature and immature fish first appeared in May (age 1+ years). Following September (age 1+ years), there was also a significant interaction between smolting and maturity. Previously mature and immature age 2+ year smolts were not significantly different in size, but immature age 2+ year non-smolts were much lighter than mature age 2+ year non-smolts. Based on mass differences, the apparent 'decision' to smolt occurred c . 5 months before (winter, age 0+ years) the decision to mature (late spring, age 1+ years). In addition to strong seasonal growth variation, sizes of freshwater Atlantic salmon were largely structured by the complex interaction between smolt-age and maturity.
Keywords:growth    life-history    seasonal variation    individual    Salmo salar
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