Estimating route-specific passage and survival probabilities at a hydroelectric project from smolt radiotelemetry studies

Abstract

A tag–release study is illustrated using radio-tagged chinook (Oncorhynchus tshawytscha) smolts to concurrently estimate passage rates and survival probabilities through the spillway and turbines of a hydroelectric project. The radio antennas at the forebays of the dam were arranged in double arrays allowing the estimation of route-specific detection probabilities and converting smolt detections to estimates of absolute passage. A maximum likelihood model is presented using the downstream detection histories to jointly estimate the route-specific passage and survival probabilities. In turn, these estimates were combined to estimate smolt survival through the dam, pool, and the entire hydroelectric project. The detailed migration information derived by these techniques can be used to evaluate mitigation programs focused on improving downstream passage of migrating salmonid smolts. At a mid-Columbia River hydroproject, the average spillbay survival calculated across replicate releases of hatchery and run-of-river yearling chinook salmon smolts was 1.000 ( estimated standard error, [Formula: see text] = 0.0144). Average survivals through the two different powerhouses at the hydroproject were estimated to be 0.9409 ([Formula: see text] = 0.0294) and 0.9841 ([Formula: see text] = 0.0119). Project survival after combining the route-specific survival and passage probabilities was estimated across stocks to be 0.9461 ([Formula: see text] = 0.0016).