Smolt Monitoring Project Week 7: Interrogations

Besides providing a way to collect salmon and steelhead smolts to insert new PIT tags, the Salmon and Snake River fish traps are mainstem PIT tag interrogation sites.  What this means is that since some fish were already PIT-tagged upstream at other locations, those fishes are scanned for preexisting PIT tags here.  We are able to learn more about their migration timing downstream. 

Hydroelectric dams, fish traps, and instream PIT tag antennas throughout the Columbia Basin corridor read the tags when fishes swim past interrogation antennas that log the tag code onto a reader.  This information is loaded into the central database, PTAGIS (, and then used to help unveil the migration history of the fishes.  It allows fisheries managers and others to monitor juvenile and adult salmonids’ journey.

The Snake River smolt trap actively scans each fish as it enters the livewell.  Consequently, we can see exactly when they enter, 24/7.  The Salmon River smolt trap has a different configuration (attached video).  The fishes are manually scanned each morning when the crew processes them for PIT-tagging. In both instances, this gives us information on when fish are moving past these locations on their way to the ocean.

To see how biologists can use such interrogation information, please read the previous article titled Rapid River Hatchery Chinook and Natural Origin Chinook: The Same but Different

Idaho Department of Fish and Game and the Fish Passage Center cooperatively operate this fish trap as a key component of the Smolt Monitoring Program and the Comparative Survival Study. More information about these important wild salmon and steelhead trout projects is available at

For more information on Idaho’s wild salmon and steelhead click here.

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    Scott Putnam