Bowerman, T., Neilson, B. and P. Budy. 2014. Effects of fine sediment, hyporheic flow, and spawning site selection on survival and development of bull trout embryos. Canadian Journal of Fisheries and Aquatic Sciences 71: 1–13. doi.org/10.1139. USGS FSP: IP-049185.
Successful spawning is imperative for the persistence of salmonid populations, but relatively little research has been conducted to evaluate factors affecting early life-stage survival for bull trout (Salvelinus conﬂuentus), a threatened char. We conducted a ﬁeld experiment to assess the relationship between site-speciﬁc environmental factors and bull trout embryo survival and fry emergence timing. Survival from egg to hatch was negatively related to percent ﬁne sediment (<1 mm) in the redd and positively related to the strength of downwelling at spawning sites. Survival of eggs to fry emergence was also negatively related to ﬁne sediment, and the best statistical models included additional variables that described the rate of downwelling and intragravel ﬂow within the incubation environment. Fry emerged at an earlier stage in development from redds with high percentages of ﬁne sediment. Increased hydraulic conductivity via redd construction and selection of spawning sites with strong downwelling appear to enhance hyporheic ﬂow rates and bull trout egg survival, but early life-stage success may ultimately be limited by intrusion of ﬁne sediment into the incubation environment.