Using Passive Integrated Transponder (PIT) Tags to Document Use of the Columbia River Estuary By Interior Salmon and Steelhead Stocks

Declines in salmon and steelhead abundance in the Columbia River have prompted basin-wide recovery efforts for the last 20 years. Recent recovery measures have focused on estuary restoration but questions remain about the potential benefits to upper-basin stocks. Lower Columbia River stocks predominate in shallow-water estuarine habitats, and interior stocks are presumed to use deeper channels and migrate quickly through the estuary.

During 2008-2013 we deployed passive integrated transponder (PIT) detection arrays at various off-channel marshes and sloughs in the tidally influenced portion of the Columbia River. We detected Chinook Salmon, Coho Salmon, and Steelhead Trout that had been previously tagged from upriver sources. These fish represented 15 evolutionarily significant units (ESUs) and distinct population segments (DPSs), 10 of which are listed under the Endangered Species Act. Both steelhead and Chinook Salmon traveled >1400 km from the Snake River Basin and > 900 km from the upper Columbia River. Outmigrating salmonids were most frequently detected, but we also detected returning fish.

This study documents off-channel estuarine habitat use by fish of known interior Basin origin, providing new insights on the diversity of stocks that occupy shallow-water habitat and therefore, may benefit directly from estuary restoration.