Migration Behavior and Distribution of Pacific Lamprey in the Upper Willamette Basin

Pacific lamprey (Entosphenus tridentatus) in the Pacific Northwest have declined dramatically in recent decades, yet very little is known about their migration behavior and habitat use. If Pacific lamprey are to persist into the future, these information gaps will need to be filled. Pacific lamprey are anadromous cold water fish that start their spawning migration in the early spring and reside in freshwater for approx. one year before spawning. The Willamette Basin was chosen to conduct a two year study of adult lamprey migration behavior and distribution. From May to August of 2009 and 2010 a total of 367 lampreys were radio-tagged over Willamette Falls. Twenty-one radio telemetry sites were installed on the main stem and major tributaries of the Willamette River. The majority of movement occurred from mid May to mid August. This time encompassed the new run entering the system and last year’s run spawning time. During spawning time, from May to July, lampreys were observed in the main stem as well as entering the tributaries. During active migration, tagged lamprey distributed in three clusters throughout the upper basin in the main stem (RKM 56-72, RKM 174 and RKM 258-290) traveling 0-9 miles a day, typically during night and early-morning hours. A range of migration behavior has been observed. Early spring movement peaked at 11°C and early summer movement at 21°C. Further identification and characterization of freshwater habitat utilized by migrating adult Pacific lamprey could be critical to sustaining populations throughout the Pacific Northwest.