Breeding location choice in salmon: causes (habitat, competition, body size, energy stores) and consequences (life span, energy stores)

Authors

  • Andrew P. Hendry,

  • Ole K. Berg,

  • Thomas P. Quinn


A. P. Hendry, O. K. Berg and T. P. Quinn, School of Aquatic and Fishery Sciences, Univ. of Washington, Box 355020, Seattle, WA 98195, USA (present addresses: APH: Organismic and Evolutionary Biology Program, Univ. of Massachusetts, Amherst, MA 01003-5810, USA [ahendry@bio.umass.edu]; OKB: Dept of Zoology, Norwegian Univ. of Science and Technology, NTNU, N-7491 Trondheim, Norway).

Abstract

Breeding location choice provides a mechanism by which individuals can directly influence their reproductive success. Location choice should therefore reflect individual condition, habitat features, and the intensity of competition; with these factors then influencing reproductive success. To test whether such patterns were detectable in the wild, we tagged 705 sockeye salmon (Oncorhynchus nerka) in a natural population, and monitored them from when they started breeding until they died. We evaluated the role of individual condition (size, secondary sexual traits, energy stores) in the acquisition of breeding locations that differed in the intensity of competition (female density, sex ratio) and habitat features (water depth, water velocity). We then evaluated the influence of breeding location on reproductive life span and energy stores. At a coarse level (20-m stream sections), females consistently settled in certain locations, and these locations sustained high densities and held larger females. At a fine scale (0.5-m breeding sites), (1) larger fish occupied deeper water (males, r2=0.072; females, r2=0.199), (2) higher levels of competition reduced reproductive life span for males (r2=0.139) but not females, and (3) fish with shorter reproductive life spans died with more energy remaining in their muscle tissue (males, r2=0.414; females, r2=0.440). These patterns were nested within a tendency for late breeding fish to have shorter reproductive life spans. Energy stores and secondary sexual traits did not influence breeding location choice, and larger fish did not acquire locations of higher intrinsic quality (i.e., those sections settled first and sustaining higher competition). Our study provides evidence that some aspects of individual condition influence breeding location choice, which then influences components of reproductive success.

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