In 2008, a total of 644 spring, 904 summer, and 1280 fall Chinook salmon (Oncorhynchus tshawytscha) were tagged with 12.5 mm PIT tags at Bonneville Dam between April 15 and October 14. An additional 312 spring and 235 summer Chinook salmon were tagged with 8.5 mm PIT tags; however, poor detection at some dams (principally Priest Rapids, Rock Island, and Rocky Reach Dams where 64.3%, 41.9%, and 12.6% respectively were not detected) resulted in these data being ignored in calculating results. After adding previously tagged fish, and subtracting fish that likely shed PIT tags, a total of 663 spring Chinook, 913 summer Chinook, and 1285 fall Chinook were tracked upstream. Data collected from the upstream migration of these fish were used to (1) compare detection rates of different PIT tag models, (2) evaluate migration speed and timing, and (3) estimate abundance of different species.

Based on PIT tag detections, 63.6% of spring Chinook salmon passed upstream of McNary Dam, 9.9% upstream of Rock Island Dam, 3.3% upstream of Wells Dam, and 41.3% upstream of Lower Granite Dam. For summer Chinook salmon, 81.7% passed upstream of McNary Dam, 49.5% upstream of Rock Island Dam, and 26.1% upstream of Lower Granite Dam. For fall Chinook, 56.5% of fall Chinook salmon passed upstream of McNary Dam, 5.5% upstream of Rock Island Dam, and 15.3% upstream of Lower Granite Dam.

Between Bonneville and McNary Dams, spring Chinook averaged 34.2 km/day, summer Chinook 33.5 km/day and fall Chinook 37.6 km/day. There was not a significant linear relationship between flow or water temperature and migration rate between Bonneville and McNary Dams.

Age composition estimates, based on scale pattern analysis, indicate that those summer Chinook salmon passing upstream of Ice Harbor Dam are predominantly yearling outmigrants (58.0% Age 1.2 and 33.6% Age 1.1), while those passing upstream of Rock Island Dam are a mixture of subyearling and yearling outmigrants (31.8% Age 1.2, 26.8% Age 0.3, 15.2% Age 1.3, and 13.3% Age 0.2 with smaller percentages from other age classes).

Mark-recapture techniques were used to estimate summer Chinook salmon abundance at upstream dams. These techniques estimated from 12.6% less to 13.0% more fish at mainstem dams upstream of Bonneville Dam than visual fish counts from fish ladders at those dams.