Movement and Behavior of Migrating Lamprey in Relation to Fishway Modifications at Priest Rapids Dam

The travel rate and proportional success of Pacific Lamprey passing upstream through hydroelectric dams on the Columbia River has been intensively researched over the past decade.  Studies have documented specific locations in fishways where the upstream movement of lamprey appeared to be impeded.  In response, several hydroelectric facilities have initiated modifications to fish ladder flow and structures in an effort to facilitate timely and successful upstream movement.  At Priest Rapids Dam (PR), lamprey passing the fish counting crowder and some sections of the fishways with diffusion grating were observed to have relatively longer travel times and lower passage success compared to other sections of the fishways.  Grant PUD installed flat plating on the floors at these locations to add surface area for lamprey to orally attach.  Plating was installed around the perimeter of floor diffusion grating, on the floor through weir orifices with adjacent diffusion grating, and as a ramp where weir orifices are elevated above the fishway floor.  Further, the fish crowder structures used to guide fish through a counting chute were newly fabricated with plating as a ramp to the count window orifice and along the crowder’s floor edge.  During the 2010 upstream migration period, underwater cameras were deployed at PR in one fishway pool with diffusion grating and on the downstream side of one crowder to evaluate lamprey movement, behavior, and passage success in relation to the newly installed plating.  Positioning, timing, relative speed, height off structure, number of oral attachments to structure, and number of pass attempts was determined.  A total of 23 lamprey events were recorded at a weir orifice.  Of these, 100% successfully passed through the orifice and all attached to or were guided by the new plating.  All lamprey were moved through the bottom half of the orifice and 90% attached on the floor below the orifice to stage before passing upstream.  On average, a lamprey took 1 minute and 22 seconds to pass through the orifice.  A total of 123 lamprey events were recorded at the fish crowder.  Lamprey were observed to successfully pass through the fish crowder for 71% of the events and of these, 43% attached to or were guided by the plated ramp.  We conclude that floor plating through the weir orifice provided for short travel times and high rates of passage success to lamprey, however plating on the fish crowder appeared inconsequential to lamprey passage success.