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First-of-its-kind study in King County tracks migration patterns of threatened chinook salmon in the Green-Duwamish River


Natural Resources and Parks
Public Affairs

First-of-its-kind study in King County tracks migration patterns of threatened chinook salmon in the Green-Duwamish River


Scientists with the King County Department of Natural Resources and Parks placed small transponders inside young, wild and hatchery chinook salmon to collect valuable data on how the threatened salmon use habitat in the Green-Duwamish River as they migrate. Movements of the fish were recorded as they passed a specialized floating antenna in the river near Tukwila.


King County scientists are using advanced technology to study the migratory patterns of juvenile chinook salmon in the Green-Duwamish River, providing valuable data that will inform future habitat protection and restoration projects that help ensure the threatened species’ survival.

Scientists with the Department of Natural Resources and Parks placed a small a device – known as a Passive Integrated Transponder tag – inside young salmon in the upper watershed. They placed an antenna receiver downstream in Tukwila that records data as each fish swims past, letting biologists know if the salmon made it down the river and how long it took to get there.

Each tag contains a unique identification number, making it possible for King County biologists to track each fish’s migration, including its origin and size when it was tagged.  This helps them understand how fish are using Green-Duwamish River habitat on their way to Puget Sound where chinook provide sustenance for southern resident orcas.

Experts from King County’s Water and Land Resources Division and the state Department of Fish and Wildlife set up a portable fish trap in the middle Green River near Auburn where they capture small fish as they move downstream. They then inject tiny transmitters not much larger than a piece of long-grained rice before releasing the juvenile chinook back into the river.

A barge securely cabled to the pillars of a bridge spanning the lower Green River is outfitted with highly sensitive equipment that records the unique data from each tagged salmon as they swim by toward Elliott Bay.

Results from the study have revealed previously unknown information about the secret lives of Green-Duwamish chinook. Prior to this study, it was often assumed that young chinook passed through the lower part of the river quickly. Data from tag detections shows that these young fish spent as much as two months in the river before leaving with smaller fish staying longer than larger ones. This tells scientists that habitat restoration in the lower Green River – especially those focused on providing habitat for these smaller fish – will help King County and its partners recover Chinook populations.

“We have a longstanding commitment to protect and restore chinook salmon habitat to help recover depressed populations,” said project lead Chris Gregersen, a fisheries ecologist with the King County Water and Land Resources Division. “With this research, we can help identify where these fish are actually going to be living and help us tailor our restoration projects to have the most benefit.”

The project is led by the Science and Technical Support of Section of King County’s Water and Land Resources Division, which provides scientific research, information, and analysis in support of regional environmental resource management in King County.

Funding for the research has been provided by the National Estuary Program through Puget Sound Partnership, King County Flood Control District’s Cooperative Watershed Management Grants through WRIA 9, and the King County Rivers and Floodplain Management Section.

“Habitat in the lower Green River is really important for these little fish, and we need to make investments in this urban basin and not just focus on more rural areas,” said Katie Beaver, King County’s Green-Duwamish River Basin Steward.

Relevant links

For more information, contact:

Anita Kissée, Department of Natural Resources and Parks, 253-218-7155