Monitoring the Use of the Mainstem Columbia River by Bull Trout from the Walla Walla Basin Annual Report 2008

Bull trout distribution, abundance and habitat quality have declined range wide and several local

extirpations have been documented. As a result, the Columbia River Distinct Population

Segment of bull trout was listed as threatened under the Endangered Species Act in June 1998.

Mainstem Snake and Columbia River dams have the potential to impact migratory bull trout.

Little is known about use of the Columbia River by bull trout from the Walla Walla Basin and

the need for further research is identified in the U.S. Fish and Wildlife Service Draft Recovery

Plan. A full stream width passive integrated transponder (PIT) array was maintained in the lower

Walla Walla River and used to monitor use of the Columbia River by bull trout from the Walla

Walla Basin from October 2007 through September 2008. We PIT tagged 158 bull trout in the

Walla Walla Basin during the year, including a significant number lower in the Basin near the

Burlingame Diversion facility. Additional bull trout tagged by other agencies in Mill Creek

(tributary to the Walla Walla River), the South Fork Walla Walla River, and the Touchet River

were also available for detection. Six PIT tagged bull trout were detected moving through the

lower Walla Walla River toward the Columbia River from November 2007 through January

2008. Additional PIT tagged bull trout may have passed the array undetected when detection

efficiencies were relatively low. Since only a small proportion of Walla Walla Basin bull trout

are PIT tagged, these six detections likely represent some larger number of bull trout exhibiting a

similar pattern of movement. In addition, a Walla Walla Basin bull trout from the Touchet River

was detected in the juvenile fish bypass at John Day Dam on the Columbia River.