Predicting benefits of spawning-habitat rehabilitation to salmonid (Oncorhynchus spp.) fry production in a regulated California river

We tested the hypothesis that spawning-bed enhancement increases survival and growth of chinook salmon (Oncorhynchus tshawytscha) embryos in a regulated California stream with a gravel deficit. We also examined how 12 physical parameters correlated within spawning sites and how well they predicted survival and growth of chinook salmon and steelhead (Oncorhynchus mykiss) embryos. Salmon embryos planted in enhanced gravels had higher rates of survival to the swim-up stage than embryos planted in unenhanced spawning gravels. No significant increase in growth was observed. Intergravel temperature and substrate size were strongly correlated with distance downstream from the lowest nonpassable dam. Intergravel turbidity and total suspended and volatile solids were also strongly correlated. Multiple-regression models were built with a combination of physical measurements to predict survival and length of salmon and steelhead embryos. Survival models accounted for 87% of the variation around the mean for salmon and 82% for steelhead. Growth models accounted for 95% of the variation around the mean for salmon and 89% for steelhead. These findings suggest that spawning-bed enhancement can improve embryo survival in degraded habitat. Additionally, measurements of a suite of physical parameters before and after spawning-bed manipulation can accurately predict benefits to target species.