Gravel to Gravel: The Use of PIT Tags to Monitor Salmon and Steelhead Populations in the Columbia Basin

Each year, researchers in the Columbia Basin mark more than two million juvenile Pacific salmon Oncorhynchus spp. and steelhead O. mykiss with passive integrated transponder (PIT) tags.  Hundreds of thousands of these tagged fish are passively detected as they migrate down the Columbia and Snake rivers and their tributaries to the Pacific Ocean from natal rearing locations across Idaho, Oregon, Washington, and British Columbia.  Thousands of these same PIT-tagged fish are again detected as adults when they return from the ocean and re-ascend the Columbia River and its tributaries.  Smolts marked with both PIT and acoustic tags have been subsequently detected along the Pacific coast from the Columbia River Estuary to southeast Alaska, extending the compiled life history of an individual PIT-tagged fish to include its early ocean experiences.  The use of PIT tags, alone and in conjunction with other marks, provides resource managers with a robust set of data with which to monitor the response of salmon and steelhead populations to naturally-occurring changes in environmental conditions within the Columbia Basin, and evaluate their response to controlled alterations to operations at the Basin’s numerous hydroelectric dams.