Monitoring Bull Trout Reintroduction in the Middle Fork Willamette River, Oregon

Bull trout declines in the Willamette Basin have been attributed to habitat fragmentation and degradation, angling-related mortality, eradication efforts, diminished productivity associated with loss of Chinook salmon, and introduction of nonnative species.  Construction of high-head dams lacking functional fish passage in the 1960s isolated previously interconnected, fluvial populations, and by 1997 the population upstream of Hills Creek Dam was considered extirpated.  Reintroduction efforts in 1997–2005 involved translocation of 10,408 bull trout fry directly from the McKenzie River basin to the M. Fk. Willamette River basin.  We documented natural reproduction stemming from direct transfers of fry in small (<500 m) spring creeks beginning in 2005 but not in a 10-km tributary that received fry.  In 2006, management agencies decided to switch to a captive-rearing program that resulted in the release of 2,567 larger age-0 and age-1 juveniles into this tributary during 2007–2013.  We monitored the effectiveness of reintroduction efforts by conducting snorkeling, minnow-trapping, and spawning surveys, and by operating remote PIT tag interrogation systems and traps designed to catch post-spawn adults.  We first confirmed spawning by captive-reared fish in 2014.  Continued monitoring will provide the basis for evaluating long-term success of various reintroduction approaches.