Research, monitoring, and evaluation of emerging issues and measures to recover the Snake River fall Chinook salmon ESU

Abstract

The portion of the Snake River fall Chinook Salmon Oncorhynchus tshawytscha ESU that spawns upstream of Lower Granite Dam transitioned from low to high abundance during 1992–2017 in association with U.S. Endangered Species Act recovery efforts and other federally mandated actions. This annual report focuses on (1) numeric and habitat use responses by natural- and hatchery-origin spawners, (2) phenotypic and numeric responses by natural-origin juveniles, (3) USGS use of a small unmanned aerial system (sUAS) to search for fall Chinook salmon redds and carcasses, and (4) the detection of 8-mm PIT tags at Lower Granite Dam. Spawners have located and used most of the available spawning habitat and that habitat is gradually approaching redd capacity. Timing of spawning and fry emergence has been relatively stable; whereas the timing of parr dispersal from riverine rearing habitat into Lower Granite Reservoir has become earlier as apparent abundance of juveniles has increased. Growth rate (g/d) and dispersal size of parr also declined as apparent abundance of juveniles increased. Passage timing of smolts from the two Snake River reaches has become earlier and downstream movement rate faster as estimated abundance of fall Chinook Salmon smolts in Lower Granite Reservoir has increased. These findings coupled with stock-recruitment analyses presented in this report provide evidence for density-dependence in the Snake River reaches and in Lower Granite Reservoir that was influenced by the expansion of the recovery program. The long-term goal is to use the information covered here in a comprehensive modeling effort to conduct action effectiveness and uncertainty research and to inform Fish Population, Hydrosystem, Harvest, Hatchery, and Predation and Invasive Species Management RM&E. In 2017, the USGS searched 15 shallow water spawning sites in conjunction with the Idaho Power Company (IPC). Redd counts agreed with those of IPC for a little more than half the sites suggesting that we need more training in redd counting. We recovered 67 carcasses, and tissue samples are currently being analyzed for parentage to ultimately determine the percentage of hatchery-origin spawners on the spawning grounds. Redd fading was examined to determine the frequency at which aerial surveys should be conducted. Most redds surveyed through time were visible for at least 4 weeks after the redd was initially constructed. Redd fading was variable amongst sites and depended on location. In 2017, we conducted a second year of evaluating detection efficiency of 8-mm PIT tags in the Lower Granite Dam juvenile fish collection system. Groups of 75–78 fish were tagged with 8-mm Biomark, 8-mm Oregon RFID, 9-mm Biomark, and 12-mm Biomark PIT tags and released into the bypass upstream of the upwell. From 97.4 to 100% (depending on tag type) of tagged fish were detected on at least one antenna in the Lower Granite Dam bypass system. Mean detection efficiency within the predominant passage route (i.e., diversion river exit) exceeded 0.98 for all tag types in both years. These results suggest that fish tagged in the field with 8-mm PIT tags should be detected at rates similar to larger tags at main-stem hydroelectric dams.