Acoustic telemetry of California sea lions in relation to adult salmonids in the bonneville dam tailrace

Acoustic pingers (ultrasonic transmitters) were attached to six California sea lions captured at Bonneville Dam to track movements and infer salmonid foraging behavior near Bonneville Dam and the lower Columbia River in 2009.  Receivers were located from Bonneville Dam to the Columbia River mouth (approximately 240 river km).  Sea lions were tracked for 6 to 44 days.  Of the four animals with relatively long datasets, three foraged almost exclusively in the Boat Restricted Zone of the tailrace, while the fourth made daily foraging trips of approximately 8 km downriver from the dam.   Detection data showed that approximately 90% of the detections of these animals occurred during the day and twilight hours.  These animals spent approximately 10 of 106 nights away from the favored haul-out site in the tailrace during their stay at Bonneville Dam.  All four of these animals made at least one trip to the river mouth and back to Bonneville Dam subsequent to tagging and prior to the end of May. One animal (C697) made two such trips.  Three of the instrumented sea lions were opportunistically detected by other researchers using acoustic arrays located near Cascade Head in the Pacific Ocean (~132 km south of the Columbia River).