The influence of redd site selection, groundwater upwelling, and over-winter incubation temperature on survival of bull trout (Salvelinus confluentus) from egg to alevin

We measured survival of bull trout (Salvelinus confluentus) embryos to the alevin stage in areas selected and not selected by females for spawning. In this study we tested the hypotheses that (1) females are utilizing habitat s influenced by discharging groundwater and that (2) there is a reproductiv e advantage to spawning at these selected sites. Embryo survival was assess ed by placing fertilized eggs in capsules that could be retrieved once they were placed in selected and nonselected locations. The survival rate was s ignificantly higher (88.6 vs. 76.1%) and less variable in the selected area , but alevin lengths did not differ significantly between areas. The select ed areas were, on average, locations of groundwater discharge and higher wa ter temperatures over the incubation period, while nonselected locations we re in areas of surface-water recharge and lower water temperatures. The res ults suggest that appropriate reproductive habitats which offer the best in cubation environments may be limited in bull trout systems, and that site s election by females may increase fitness and be critical for population via bility.