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Influence of breeding habitat on bear predation and age at maturity and sexual dimorphism of sockeye salmon populations

Canadian Journal of Zoology

By:
, , , , and
https://doi.org/10.1139/z01-134

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Abstract

Age structure and morphology differ among Pacific salmon (Oncorhynchus spp.) populations. Sexual selection and reproductive capacity (fecundity and egg size) generally favor large (old), deep-bodied fish. We hypothesized that natural selection from physical access to spawning grounds and size-biased predation by bears, Ursus spp., opposes such large, deep-bodied salmon. Accordingly, size and shape of salmon should vary predictably among spawning habitats. We tested this hypothesis by measuring the age composition and body depth of sockeye salmon, Oncorhynchus nerka, and the intensity of predation in a range of breeding habitats in southwestern Alaska. Stream width was positively correlated with age at maturity and negatively correlated with predation level. However, salmon spawning on lake beaches were not consistently old, indicating that different factors affect age in riverine- and beach-spawning populations. Body depths of male and female salmon were positively correlated with water depth across all sites, as predicted. However, the mouths of some streams were so shallow that they might select against large or deep-bodied salmon, even in the absence of bear predation. Taken together, the results indicated that habitat has direct and indirect effects (via predation) on life history and morphology of mature salmon.

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Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Influence of breeding habitat on bear predation and age at maturity and sexual dimorphism of sockeye salmon populations
Series title:
Canadian Journal of Zoology
DOI:
10.1139/z01-134
Volume:
79
Issue:
10
Year Published:
2001
Language:
English
Publisher:
NRC Research Press
Contributing office(s):
Western Fisheries Research Center
Description:
12 p.
First page:
1782
Last page:
1793
Country:
United States
State:
Alaska
Online Only (Y/N):
N
Additional Online Files (Y/N):
N