Characterizing Juvenile Steelhead Abundance, Growth, and Survival at Multiple Spatial and Temporal Scales During the Pretreatment Period of Large Restoration Experiment

Fish production is often used as quantitative measure of population performance and is key goal of steelhead and salmon recovery. Three key metrics of freshwater production are abundance, growth, and survival. By using individually marked fish more precise estimates of these metrics are now possible. A multitude of abiotic and biotic factors can influence growth and survival and these factors vary in both space and time. Differences in the fish metrics across reaches and streams can help identify limiting factors that can be addressed with stream restoration. In this study, we report the results of investigations on the abundance, growth, and survival of juvenile steelhead in three tributaries to Asotin Creek in southeast Washington. These metrics will be used as response variables to determine the effect of a large scale (12 km) riparian fencing and large woody debris treatment that will occur in a tributary to Asotin Creek in southeast Washington. Since 2008 we have captured and tagged juvenile steelhead > 70 mm in a total of 12 reaches (500 m long) within one treatment and two control streams in Asotin Creek. Capture and tagging takes place during two sessions: summer and fall. Passive (fixed) and portable (mobile) PIT tag antennas are used detect PIT-tagged fish during three interval periods: early fall, winter, and early spring. These data were used to characterize steelhead metrics during three years of pre-treatment monitoring. Preliminary results show that growth varies significantly between age classes, reaches within streams, and between streams. There was no apparent correlation between growth and abundance. Summer survival estimates were very high (> 70-95%) for all reaches and varied less between reaches, streams, and years. Spring, fall and winter survival was much lower than summer survival (5-70%) and varied considerably across spatial and temporal scales. We hypothesize that winter survival may be a limiting factor and that the restoration treatment may improve winter survival by providing more cover. We also discuss the implications of these findings in the context of the final restoration study design.