Marine Mammal Predation in the Lower Columbia River
Predation and invasive species management RM&E components included –estimating sea lion abundance and predation by sea lions, using two methods, video-based and tandem boat surveys. We detected 1,132 events of sea lions recorded on video records over a 20 day period from the area upstream of Tanner Creek and beyond the US Army Corps of Engineers observation area. Predation was observed in 8.1% of these observations. Overall, we recommend moving away from video-based abundance estimation toward using tandem boat surveys. Our weekly tandem boat surveys resulted in abundance estimates ranging from 54 to 11 sea lions located between the I205 Bridge and Tanner Creek (approximately 34 river miles). Status and trend monitoring was accomplished by tracking three individual CSLs outfitted with GPS phone tags. Two instrumented CSLs made multiple trips to Astoria and back to Bonneville Dam during the season, a phenomenon that we have previously documented. The third CSL remained near Bonneville Dam for the nearly 3 weeks of tracking. Individuals did show affinity for particular areas near Bonneville Dam.
Predator Control components included non-lethal hazing sea lions. The boat-based crew from CRITFC hazed sea lions for a total of 31 days from 3/05/2012 to 5/18/2012. Hazing resulted in 288 hazing events on 112 and 371 California sea lions and Steller sea lions, respectively. A total of 1,183 cracker shells and 401 seal bombs were used during deterrent activities. The final direction of sea lions at the end of these encounters resulted in 74.3% of sea lions moving down stream of the hazing boat.