Going and Coming: Survival and Timing of PIT-Tagged Juvenile and Adult Salmonids in the Columbia River Estuary

Nearly two decades of research and development have contributed to an elaborate fish monitoring network that covers the Columbia River.  This network is based on interrogations of juvenile and adult salmon bearing passive integrated transponder (PIT) tags and provides high‑quality data for estimates of reach survival and timing.  Fish transport systems have been developed to enhance survival and to work with PIT technology to control the timing of transport operations, which convey fish to release points below Bonneville Dam, the lowermost dam in the hydrosystem.  Detection data from below Bonneville Dam are needed to estimate survival through the entire hydrosystem and bolster individual reach estimates.  In 1995, we began efforts to detect PIT-tagged fish in the tidal freshwater portion of the upper estuary (rkm 61-83) using a surface pair trawl fitted with a PIT-tag detection system to complete these estimates and to compare inriver‑migrant and transported juveniles.  In 2011, we established a stationary detection array in the same reach where the trawl is operated.  The new system provides estimates of adult survival and timing to Bonneville Dam.  We present methodologies used to obtain these detections in a large estuarine environment, along with nearly two decades of survival and timing data.