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Abstract
Passage facilities at dams must accommodate a broad array of aquatic species to achieve full river connectivity. In an attempt to improve adult Pacific lamprey (Entosphenus tridentatus) passage, fishway entrance modifications were made at a large dam on the Columbia River in northwestern USA. The modifications consisted of a variable-width entrance weir and flow disrupters to create heterogeneity in water velocities near the bottom, without affecting attraction flows for adult salmonids (Oncorhynchus spp.) or alosids (Alosa sapidissima). Additionally, a lamprey passage structure (LPS) was installed to provide a lamprey-specific route from tailrace to forebay elevation (31 m). Passive integrated transponders and radio transmitters were used to monitor both Pacific lamprey and Chinook salmon (O. tshawytscha) movements. Fish use of the modified entrance was compared to that at a similar, but unmodified entrance before and after modifications. The entrance modifications resulted in increased velocity heterogeneity, but no measurable improvement in entrance efficiencies for lamprey or salmon. Lamprey successfully ascended the LPS, with annual counts ranging from 48 in 2010 to 3,851 in 2016 (0.2–8.9% of lamprey counted at the dam). Radiotelemetry indicated that tagged lamprey resumed upstream passage after LPS use and travelled at rates similar to those that used traditional fishway routes.
Acknowledgments
This project would not have been possible without the vision of D. Clugston, U.S. Army Corps of Engineers (USACE). We thank S. Schlenker, S. Tackley, and AECOM for measurements of hydraulic conditions and modeling work. J. Simonson, J. Moser, B. Wassard, and G. Wolf contributed to the fabrication and installation of the LPS. B. Sandford, J. Butzerin, and D. Dey provided editorial comments. The manuscript was much improved by suggestions from M. Lucas and an anonymous reviewer. Fish biologists H. Pennington, D. Quaempts, B. Treloar, C. Schilt, M. Hanks, E. Johnson, C. Noyes, D. Joosten, T. Clabough, K. Tolotti, R. Ringe, S. Lee, M. Kirk, W. Daigle, T. Dick, B. Burke, and M. Jepson and many more contributed to fish collection, tagging, data collection and database management. L. Stuehrenberg, T. Bjornn, and C. Peery were principal investigators during the early years of work, all of which was funded by the USACE, Portland District.
Disclosure statement
No potential conflict of interest was reported by the authors.