Riverscape Heterogeneity and Homing Behavior of Spawning Spring Chinook Salmon at Multiple Scales

Spawning site selection by female salmon is based on complex tradeoffs between homing instinct and the availability of habitat for successful reproduction. Previous studies have shown that female hatchery-origin Chinook salmon released from different acclimation sites return with varying degrees of fidelity to these areas. We hypothesized that associations between spawning site selection and aquatic habitat factors vary across spatial scales and affect homing fidelity.  To investigate the possibility that homing fidelity is associated with aquatic habitat conditions, we quantified physical habitat throughout 160 km in the upper Yakima River basin (Washington, USA) and compared these data to redd and carcass locations that were mapped during five spawning seasons (2004-2008). Principal components analysis identified differences in substrate, cover, stream width, and gradient among acclimation sites, and canonical correspondence analysis revealed that habitat features were associated with spatial patterns of spawning (p < 0.01). These preliminary analyses indicated that female salmon may forego spawning near their acclimation area if the surrounding habitat is unsuitable.