Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Cooling water temperature gradients in a fishway are associated with poor passage and increased potential for interactions between hatchery and wild salmon   (#205)

Chris C Caudill 1 , George P Naughton 1 , Timothy Blubaugh 1 , Tami Clabough 1 , Matthew Keefer 1 , Michael Jepson 1 , Charles T Boggs 1 , Grant Brink 1
  1. Department of Fish and Wildlife Sciences, University of Idaho, Moscow, IDAHO, United States

Effective passage is critical for fish collection facilities.  Trapping facilities with fishways are used to capture adult salmonids in the Willamette Valley, Oregon, USA below high-head dams during collection of mitigation hatchery broodstock and, more recently, the establishment of ‘wild fish sanctuaries’ above dams for ESA-listed Chinook salmon and steelhead.  However, observations of holding adults and hatchery-origin salmon spawning below Foster Dam on the South Santiam River raised concerns about the efficacy of the fishway and trap before and after a major 2014 facility upgrade.  In 2015-2016, optical video and DIDSON observations revealed substantial adult holding outside and within the fishway, and considerable milling in the upper ladder near the trap entrance.  Experimental manipulation of velocities at the powerhouse entrance increased salmon entry rate into the fishway, but not trapping rate.  In 2017, we radio-tagged 16 hatchery-origin Chinook Salmon ~30 km downstream.  All were detected in the Foster tailrace, but trap collection efficiency was low (43.7%).  Optical video monitoring at the trap entrance revealed 9.2 entrance attempts/trap entrance and that entrance rates were related to trap operations and potentially social cues from previously trapped adults.  Salmon body temperature declined from ~16°C at tagging to ~12°C in the tailrace to ~10°C at collection because fishway temperatures were strongly influenced by hypolimnetic water from Foster Reservoir.  Current hypotheses to explain observed behaviors include overall effects of cool water temperatures, temperature gradients between the Foster tailrace and adult trap, and/or a lack of natal olfactory cues in fishway waters.  The ineffective collection of adults raises concern about hatchery-wild fish interactions below the dam and reduced ability to efficiently provide passage via trap-and-haul to adults with natal origin from the wild fish sanctuary above the dam.  Results highlight the importance of effective fish passage in implementing mitigation and conservation strategies.