Passage Distributions and Federal Columbia River Power System Survival for Steelhead Kelts Tagged Above and At Lower Granite Dam

Steelhead (Oncorhynchus mykiss) populations have declined throughout their range in the last century and many populations, including those of the Snake River Basin are listed under the Endangered Species Act. The reasons for their decline are many, but include habitat loss and degradation, overharvest, and the construction of dams. Unlike Pacific salmon, which all die after they spawn, post-spawning steelhead (known as “kelts”) can migrate back to the ocean to feed and replenish their energy stores, then return to freshwater and spawn in subsequent years (known as iteroparity). However, it is estimated that <2% of Snake River steelhead are able to make a second spawning run. Kelts may be vulnerable to delays in their migration caused by mainstem dams and reservoirs in the Snake and Columbia rivers, and may also suffer high mortality while passing the dams. The primary goal of this research was to estimate route-specific survival of steelhead kelts through up to seven Federal Columbia River Power System (FCRPS) dams using the Juvenile Salmon Acoustic Telemetry System (JSATS). In addition, system wide and reach specific survival were estimated.  Passage metrics such as forebay residence, tailrace egress, and project passage timings were also calculated at each FCRPS dam.

In 2012, JSATS transmitters were surgically implanted into 324 steelhead kelts captured at Lower Granite Dam (LGR) and several tributaries in the Snake River basin. Overall, 37.0% (120 of 324) of the tagged kelts successfully migrated from LGR (rkm 695, as measured from the mouth of the Columbia River) to rkm 113 (downstream of Bonneville Dam). The majority of kelts passed the dams via spillway routes (i.e., spillway weirs, traditional spill) where survival estimates were generally higher compared to all other routes of passage (e.g., juvenile bypass systems, turbines, sluiceways). The results of this study contribute to understanding the impact of hydropower on steelhead kelt migration in the FCRPS. Specifically, this study is the first to document route-specific survival since the installation of spillway weirs at many of the dams in the FCRPS. The data may be used to adaptively manage configuration and operation of FCRPS dams to maximize kelt survival.