Influence of river conditions during seaward migration and ocean conditions on survival rates of Snake River Chinook salmon and steelhead

Petrosky CE, Schaller HA. Influence of river conditions during seaward migration and ocean conditions on survival rates of Snake River Chinook salmon and steelhead.
Ecology of Freshwater Fish 2010: 19: 520–536. © 2010 John Wiley & Sons A/S Abstract – Improved understanding of the relative influence of ocean and freshwater factors on survival of at‐risk anadromous fish populations is critical to success of conservation and recovery efforts. Abundance and smolt to adult survival rates of Snake River Chinook salmon and steelhead decreased dramatically coincident with construction of hydropower dams in the 1970s. However, separating the influence of ocean and freshwater conditions is difficult because of possible confounding factors. We used long time‐series of smolt to adult survival rates for Chinook salmon and steelhead to estimate first year ocean survival rates. We constructed multiple regression models that explained the survival rate patterns using environmental indices for ocean conditions and in‐river conditions experienced during seaward migration. Survival rates during the smolt to adult and first year ocean life stages for both species were associated with both ocean and river conditions. Best‐fit, simplest models indicate that lower survival rates for Chinook salmon are associated with warmer ocean conditions, reduced upwelling in the spring, and with slower river velocity during the smolt migration or multiple passages through powerhouses at dams. Similarly, lower survival rates for steelhead are associated with warmer ocean conditions, reduced upwelling in the spring, and with slower river velocity and warmer river temperatures. Given projections for warming ocean conditions, a precautionary management approach should focus on improving in‐river migration conditions by increasing water velocity, relying on increased spill, or other actions that reduce delay of smolts through the river corridor during their seaward migration.     

Effects of Temperature on Feeding Activity of the White River Crayfish Procambarus acutus acutus1

Feed consumption by white river crayfish Procambarus acutus acutus in a 56-d laboratory study increased at a linear rate with water temperature over a range of 5 to 25 C. Feed consumption changed as water temperatures were cycled from 20–8–20 C (0.5 C/d) over a 68-d period and was the highest at the initial 20 C level and the lowest at 8 C. As water temperature increased, feed consumption rate increased; however, consumption never reached the initial rate at 20 C. Crayfish fed 3% and 6% of body weight were significantly larger than animals fed at 1% of body weight after 8 wk. Feed conversion ratios increased significantly with feeding rate. Based on this laboratory study, white river crayfish feed most effectively when water temperature is ≥ 15 C and the feeding rate is 3% of body weight/d.     

Acute Toxicity of 5% Non-Synergized Emulsifiable Rotenone to White River Crayfish Procambarus acutus acutus and White Perch Morone americana

Annual drawdown of crayfish culture ponds to plant forage crops also serves to eradicate most predaceous finfish. Without annual drawdown predaceous fish populations may reach numbers that can significantly reduce the crayfish crop. Frequent drawdown may not be feasible or desirable in some management schemes. Evidence in the literature suggests that differential toxicity of rotenone would allow removal of fish without harming crayfish in the same pond. In the current study, laboratory and in situ acute toxicity bioassays (96 h) were conducted with 5% non-synergized emulsifiable rotenone to define the maximum non-lethal concentration (LC₁₀₀) for white river crayfish Procambarus acutus acutus and the minimum lethal concentration (LC₁₀₀) for white perch Morone americana . Six concentration levels of rotenone formulation were tested in each of six toxicity trials with crayfish using dechlorinated tap water at 21–25 C. LC₀ (compensated for control mortality) was determined to be 3.0 mg/L. Significant crayfish mortality began at 4.0 mg/L. Acute toxicity to white perch was anticipated to be within recommended concentration levels on product label for similar fish, and was corroborated by laboratory bioassay (LC₁₀₀ of 0.15 mg/L). Both species were then tested together in laboratory aquaria utilizing pond water at room temperature. Concentration levels of 0.05–2.5 mg/L killed all white perch with no crayfish mortality. In the final phase of the study a 1.0 mg/L concentration of rotenone was applied to a pond containing both species held in cages. All white perch were dead within 24 h; no crayfish mortality was observed for the 96-h duration of the trial. It may therefore be possible to use this rotenone formulation to control white perch and other finfish in active crayfish culture ponds.