Movements, habitat use, and population characteristics of adult Pacific lamprey in a coastal river

We used radio telemetry to investigate the freshwater biology of adult Pacific lampreys in the Smith River, a coastal Oregon watershed. We tagged 91 adults at a fish ladder trap (65 km from the ocean) in the spring of 2006–07 and 2009–10. We did not detect a radio-tagging effect on short-term survival and migration rate relative to a PIT-tagged cohort. Fish began migrating April–June and averaged 8.5 km/d. Most were holding by late June, which coincided with the onset of base flow and peak water temperatures. Summer holding locations were distributed 68–146 km from the ocean. Migration distance was inversely related to tagging date but was not related to fish length. Holding fish were strongly associated with glides and boulders as cover. Fish held for about 9 months prior to spawning, although 75 % made at least one upstream movement in winter coincident with high-water events. Individuals began their final migration/spawning phase in March and April, coinciding with increasing temperature and discharge, and were highly vulnerable to predation. Fish that were tagged during the initial migration and held in the upper basin mainly moved downstream to spawn, whereas fish that were tagged during the final migration moved upstream prior to spawning. Some spawned in multiple locations, separated by ≤16 km, and with 1–3 other spawners. The broad distribution of holding and spawning habitat of this population and the diverse needs of individuals suggest that conservation of coastal lamprey populations will require protection and restoration at the watershed level.