Larval Lamprey Occurrence in a Tidally-Influenced Coastal Stream

Larval Pacific lamprey tolerance to simulated tidal salinity fluctuation was evaluated in a series of controlled laboratory experiments and was a precursor for investigating whether larvae naturally occurred in an estuarine environment.  Survival through 96 h laboratory experiments was 100% and 60% in fluctuating 0 ppt to 12 ppt and 0 ppt to 15 ppt salinity, respectively.  Occurrence of larval Pacific lamprey and Lampetra spp. (western brook and river lampreys) was then investigated in a tidally-influenced segment of Ellsworth Creek (Pacific County, Washington) by electrofishing.  Larval Pacific and Lampetra spp. were detected across an approximately 300 m long tidally-influenced segment of the study area.  Salinity monitoring conducted in tidally-influenced reaches where larvae were detected indicated maximum tidal cycle salinity ranged from 12 ppt to 16 ppt, and was generally followed by freshwater (0 ppt).  These results suggest larval lampreys may be able to tolerate some exposure to salinity and occur in certain areas of estuaries and coastal basins.  Knowledge of larval lamprey distribution in estuarine environments may be valuable for habitat restoration programs, and mitigating potential impacts from dredging and other human disturbances.