Pacific lamprey (Lampetra tridentata) populations throughout the Columbia River Basin (CRB) are in decline.  Multiple reasons for the decline have been identified including passage at mainstem CRB dams and habitat degradation.  Little is known about factors limiting production in CRB tributaries.  Due to declining abundance of lamprey in the Columbia River, harvest has been limited, with the primary collection location for the four Treaty Tribes (Warm Springs, Yakama, Umatilla, and Nez Perce) at Willamette Falls on the Willamette River (Rkm 42.6) in Oregon City.  Declining lamprey populations are of primary concern to the Confederated Tribes of Warm Springs Reservation, Oregon (CTWSRO) due to their high cultural and environmental value.  Once a staple food in winter, and present at ceremonies, lamprey is often absent due to lack of availability.  Despite the cultural significance of this fishery, the first estimate of adult escapement in the Willamette River was in 2010 and occurred as a result of this study.  Prior to this estimate, harvest had been the only indicator of trends in abundance.  Harvest rates are poor indicators of abundance because they vary greatly due to increased catch regulations and restrictions.    Recent changes in Oregon fishing regulations promoted greater protection for Willamette River Pacific Lamprey.  Commercial harvest on Pacific lamprey at Willamette Falls ceased in 2002 and use of Pacific lamprey for bait was banned in 2005.