Passive integrated transponger tags are used to monitor individual fish. The tag, 12 mm long, is inserted in the fish's body cavity and contains a microchip programmed with individual fish ID codes. The system yields information about passage times of individuals at pittag observation sites.
Release cohorts were formed by combining wild fish observed at Lower Granite and at least one additional downstream site. Minimum cohort size was set at three fish. The data allowed construction of 9 'Lower Granite release cohorts' over two years.