Detection efficiency of a passive integrated transponder (PIT) tag interrogator for adult chinook salmon at Bonneville Dam, 2005

We tagged over 700 adult Chinook salmon in 2005 with both a radiotelemetry tag and a PIT tag to determine detection efficiency of the vertical-slot PIT-tag interrogator, which was installed in the Washington Shore Fish Ladder at Bonneville Dam (site code used in PTAGIS database is B04) during winter 2004-2005. Detection efficiency of B04 was very high during the spring (cumulative efficiency of 100%), when water temperatures were relatively low. However, efficiency was slightly lower in the fall (cumulative efficiency of 96%), partially due to higher water temperatures and partially to the types of PIT tags used. Differences between efficiencies recorded during the spring and fall may also be due to behavioral differences between runs ofChinook salmon, though we did not specifically test fish behavior in this study.