Predation on Chinook Salmon Smolts by Great Blue Herons
Predation on smolts as they out-migrate down natal rivers may significantly contribute to the decline and lack of recovery of Chinook salmon in British Columbia. A prior study of mortality of Chinook smolts released by the Cowichan Hatchery suggests only a small portion of the fish reached the ocean due to predation by raccoons, river otters, mergansers and trout. The goal of this study is to analyze the data collected from Chinook smolts equipped with PIT-tags in 2016 and 2017 to estimate mortality rates (from antennae arrays that recorded movements of marked fish, and scans of predator latrines for PIT-tags), and determine sources of predation (from camera-traps and antennae arrays where animals passed; as well as from tags recovered in scats). These data are needed to confirm the apparent high rates of mortality, and provide better information about who the predators are and where and when predation is occurring.