Emigration of Natural and Hatchery Chinook Salmon and Steelhead Smolts from the Imnaha River, Oregon, October 20, 1999 to June 15, 2000 : 2000 Annual Report.

This report details the smolt performance of natural and hatchery chinook salmon and steelhead from the Imnaha River to the Snake River and Columbia River dams during migration year 2000. Flow conditions in the Imnaha River and Snake River were appreciably lower during May and June in 2000, compared to historic levels at gauging stations, but flow conditions in the Imnaha and Snake River were above average during April. Overall, water conditions for the entire Columbia River were characterized by the Fish Passage Center as below normal levels. Spill occurred continuously at Lower Granite Dam (LGR), Little Goose Dam (LGO), and Lower Monumental Dam (LMO) from April 5, April 10, and April 4, respectively, to June 20, and encompassed the periods of migration of Imnaha River juvenile chinook salmon and steelhead, with a few exceptions. Outflow in the tailraces of LGR, LGO, and LMO decreased in May and June while temperatures increased. Chinook salmon and steelhead were captured using rotary screw traps at river kilometer (rkm) 74 and 7 during the fall from October 20 to November 24, 1999, and during the spring period from February 26 to June 15, 2000, at rkm 7. Spring trapping information was reported weekly to the Fish Passage Center's Smolt Monitoring Program. A portion of these fish were tagged weekly with passive integrated transponder (PIT) tags and were detected migrating past interrogation sites at Snake River and Columbia River dams. Survival of PIT tagged fish was estimated with the Survival Using Proportional Hazards model (SURPH model). Estimated survival of fall tagged natural chinook (with {+-} 95% confidence intervals in parenthesis) from the upper Imnaha (rkm 74) to LGR was 29.6% ({+-} 2.8 ). Natural chinook salmon tagged in the fall in the lower Imnaha River at rkm 7, which over wintered in the Snake River, had an estimated survival of 36.8% ({+-} 2.9%) to LGR. Spring tagged natural chinook salmon from the lower site had an estimated survival of 84.8% ({+-} 2.6%) to LGR. The season wide survival of spring tagged natural chinook salmon smolts from release in the Imnaha River to McNary Dam (MCN) was 67.9% ({+-} 6.3%). Post release survival of hatchery chinook salmon smolts, from release at the Imnaha River acclimation facility to the lower Imnaha River trap, was estimated at 94.7% ({+-} 4.7%). Hatchery chinook salmon, PIT tagged and released at the lower Imnaha River trap, had an estimated survival of 75.0% ({+-} 4.2%) to LGR. Estimated survival of hatchery chinook salmon smolts from the Imnaha River to McNary Dam (MCN) was 54.1% ({+-} 9.7%). Natural steelhead smolts had an estimated survival of 84.4% ({+-} 2.7%) to LGR and a survival estimate of 49.9% ({+-}12.2%) from the lower Imnaha River trap to MCN. The estimated survival of hatchery steelhead smolts to LGR was 85.8 ({+-} 2.4) and the survival from release to MCN was 40.2% ({+-}12.5%)