PNNL

Abstract

Populations of Pacific lamprey (Lampetra tridentata) in the Columbia River basin have declined drastically over the past 20 years. Possible causes include habitat degradation and instream flow obstacles, such as the mainstem hydroelectric dams on the Columbia River. To determine why lamprey populations have declined a monitoring system to track their movements was needed to determine possible impacts. Juvenile lamprey were implanted with passive integrated transponder (PIT) tags and their detection rates determined while migrating through fish bypass facilities at McNary in 2001 and 2005 and John Day Dam in 2002. Juvenile Pacific lamprey (115–178 mm) were obtained from the John Day Dam fish collection facility, transported to Pacific Northwest National Laboratory, and surgically PIT-tagged. Lamprey were allowed to recover for 3 to 4 days following PIT tag implantation and subsequently were released upstream of the PIT tag detectors at both dams. Primary detector efficiency was 98% at McNary Dam and 97% at John Day Dam. Average in-river travel time for fish released at McNary Dam and detected at John Day Dam was 16.1 d in 2001 and 10 d in 2005. Mean detection rates at McNary Dam varied from 74% for gatewell releases to 69% for the collection channel. Follow up tests in 2005 at McNary Dam showed detections rates near 100% from collection channel releases. Detection rates from forebay releases at McNary Dam were lower, ranging from 0% to 38% (mean = 21%). Mean travel times from release point to the primary detectors at McNary Dam were; forebay (492 min), gatewell (323 min), and collection channel (245 min). The detection efficiency at the primary detectors was similar to that of PIT-tagged smolts and travel time within the bypass system showed that lamprey can hold in the bypass system for prolonged periods.