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

Breeding location choice provides a mechanism by which individuals can dire ctly influence their reproductive success. Location choice should therefore reflect individual condition, habitat features, and the intensity of compe tition; with these factors then influencing reproductive success. To test w hether such patterns were detectable in the wild, we tagged 705 sockeye sal mon (Oncorhynchus nerka) in a natural population, and monitored them from w hen they started breeding until they died. We evaluated the role of individ ual condition (size, secondary sexual traits, energy stores) in the acquisi tion of breeding locations that differed in the intensity of competition (f emale density, sex ratio) and habitat Features (water depth, water velocity ). We than evaluated the influence of breeding location on reproductive lif e span and energy stores. At a coarse level (20-m stream sections), females consistently settled in certain locations, and these locations sustained h igh densities and held larger females. At a fine scale (0.5-m breeding site s), ii) larger fish occupied deeper water (males, r(2) = 0.0721 females, r( 2) = 0.199), (2) higher levels of competition reduced reproductive life spa n for males (r(2) = 0.139) but not females, and (3) fish with shorter repro ductive life spans died with more energy remaining in their muscle tissue ( males, r(2) = 0.414; Females, r(2) = 0.440). These patterns were nested wit hin a tendency for late breeding fish to have shorter reproductive life spa ns. Energy stores and secondary sexual traits did not influence breeding lo cation choice, and larger fish did not acquire locations of higher intrinsi c quality (i.e., those sections settled first and sustaining higher competi tion). Our study provides evidence that some aspects of individual conditio n influence breeding location choice, which then influences components of r eproductive success.