The ASL Zooplankton Acoustic Profiler (ZAP) located at the base of the slope of the Fraser Delta recorded this hourly image of echo-sounder backscatter between 4:00 and 5:00 UTC September 5, 2011 (21:00 – 22:00 PDT September 4, 2011, just after dusk and at rising tide). The image reveals a dense school of large fish between 10 and 20m depth, and many individual fish between 20 and 80m depth.
Although we cannot know for sure what the species are, the Pacific Salmon Commission’s troll test-fishing program indicated the presence in the vicinity for that week of both sockeye (Oncorhynchus nerka) and pink (Oncorhynchus gorbuscha) salmon with a very high proportion of pink salmon. Fish were gathering in the Strait and preparing to migrate up the Fraser River over these days. The Salmon Commission's Mission Hydroacoustic Station recorded extremely high runs a few days later, with approximately 600,000 and 800,000 salmon passing the monitoring site on Sept 7 and 8, respectively, up from 86,000 on August 31 (personal communications with Yunbo Xie of PSC).