Developing a PIT Tag Detection System for Pacific Lamprey in the Columbia River

Pacific lamprey Entosphenus tridentatus are an anadromous parasitic fish native to the north Pacific Ocean.  Numbers of Pacific lamprey along the U.S. west coast have declined drastically in recent decades but limited information on their life history significantly impaired efforts to manage and recover these populations.  Initial studies on adult migrations in the Columbia River used radio telemetry but limited tag life and potential tag effects led us to investigate the use of half-duplex passive integrated transponder (HDX PIT) technology.  A significant obstacle to overcome initially was interference between the HD and full duplex (FDX) PIT systems used to track anadromous salmonids.  Current antenna designs allow the flexibility to use both flat-plate and swim-through configurations that can be applied to most locations.  At this writing, 11 of the 13 passable mainstem dams on the Columbia River have been outfitted with HDX PIT systems and are in use to monitor adult lamprey migrations.  Detection efficiencies of individual HDX sites have been generally between 65 and 100%, with lower detection probabilities at sites monitoring larger fishway openings.  HD-PIT telemetry is generally less expensive than active tag technologies, provides unlimited tag life, and the smaller tag size has allowed tagging of the full size range of adult lamprey collected.  The limited read range of PIT technology relative to telemetry means that HDX PIT stations can not readily cover large areas in fishways (e.g. slow velocity junction pools) or open water areas such as in the tailraces of dams and not all passage metrics can be estimated with the technology. During five years (2005 to 2009), we tagged over 4,500 adult lamprey, primarily at Bonneville Dam.  Data generated from this program has allowed the development of system-wide and reach specific escapement estimates, migration timing, and multi-factorial analysis of conditions associated with migration success.