Reservoir provides cool-water refuge for adult Chinook salmon in a trap-and-haul reintroduction program

Abstract

Trap-and-haul is a mitigation strategy at many hydropower dams lacking upstream fish-passage facilities, and protocols are needed to maximise its effectiveness. We used biotelemetry to assess the potential benefits of releasing transported adult Chinook salmon (Oncorhynchus tshawytscha) into a cold-water reservoir v. a relatively warm-water tributary before spawning. Over 5 years, we released 160 salmon into Foster Reservoir (Oregon, USA) and another 102 into the South Santiam River near historical salmon spawning areas further upstream. In total, 70% of reservoir-released salmon entered an upriver tributary after spending a median of 3–95 days annually in the reservoir. Data recovered from 61 archival temperature loggers indicated that salmon were ~3–6°C cooler per day in the reservoir than in the river. We estimated that cumulative exposure of reservoir-released fish was reduced by 64 degree days, on average (range=–129 to 392), relative to river-released fish. Release into the reservoir was not risk free; 14% of all reservoir-released fish fell back downstream v. 1% of river-released fish. We conclude that reduced transport distance, reduced thermal exposure and potential survival benefits of releasing salmon into reservoirs should be weighed against risks of factors such as fallback and homing errors.

Thermal exposure of adult Chinook salmon and steelhead: Diverse behavioral strategies in a large and warming river system

“…However, several recent studies of obligate summer- and fall-spawning Pacific salmon populations suggest that behavioral thermoregulation distant from spawning sites may not be a particularly viable strategy [ 50 , 103 , 121 , 125 ]. On the other hand, the well-documented thermoregulatory behaviors that occur near natal sites during the final stages of maturation [ 126 – 131 ] will potentially be increasingly important for these populations.…”

Review of trap-and-haul for managing Pacific salmonids (Oncorhynchus spp.) in impounded river systems

“…The mean annual number of adults transported upstream during 1996-2018 was 979 Chinook salmon and 580 steelhead . Collected adults are transported upstream to several release locations, including the head of Foster Reservoir (Sharpe et al 2016;DeWeber et al 2017;Naughton et al 2018). Downstream migrants at Foster Dam pass through turbines, spillbays, or through a weir designed to facilitate downstream passage; juvenile fish passage efficiencies and survival rates have generally been higher at Foster Dam than at other Willamette Project dams (Hughes et al 2014(Hughes et al , 2016.…”

“…Fish sorting is an important element in most adult trapand-haul programs. Sorting can be used to remove non-target fish or species (e.g., hatchery-origin fish or non-native species) from the transported population, collect scale or genetic samples to assess age structure or monitor reproductive success (Sard et al 2015(Sard et al , 2016, mark or tag fish to monitor behavior and survival after fish are released (Keefer et al 2010;DeWeber et al 2017;Naughton et al 2018;Kock et al 2018a), and distribute fish in accordance with management strategies and regulatory requirements. Most adult fish collection facilities were designed with sampling stations integrated into the infrastructure of the collection facility.…”

“…Many fish experience migration delays and stress during handling and passage events, which in turn can affect swimming performance, increase disease transmission rates and infection risks, and even lead to premature death. Adult fish that pass dams volitionally or are transported upstream may fall back past the dams (Boggs et al 2004;Naughton et al 2018) or fail to locate spawning habitat, and not contribute to population productivity. Similarly, juvenile fish that use fish bypass systems or are transported may be injured or infected in these systems.…”

“…Reascension is not an option for adult salmonids that fall back via spillways or turbines at most high-head dams. Most fallback fish at these sites are lost to the anadromous population upstream of the dam, although those that escape serious injury may potentially re-enter adult traps or spawn at downstream sites (Naughton et al 2018).…”