Figure 1.
Map of the Snake River basin, showing locations of major dams and tributaries.
Water temperatures and behaviors of radio-tagged adult Chinook salmon and steelhead were monitored at Ice Harbor (IH), Lower Monumental (LM), Little Goose (LG), and Lower Granite dams in 2000-2003. In all years, cold-water releases from Dworshak Dam on the Clearwater River affected thermal layering in Snake River reservoirs downstream. Large and small color insets are representations of Lower Granite Dam (975 m long, 30 m high), including fishway features typical of the Snake River dams. Colors indicate relatively warm forebay water, cool tailrace water, and intermediate fish ladder water. The fishway is composed of multiple tailrace entrances (white stars) where fish enter collection channels leading under the spillway and/or across the face of the dam. Channels merge at a junction pool and transition area at the base of the pool-and-weir ladder where tailrace water is pumped through diffusers to provide attraction flow at entrances (dark rectangles). The mid portion of the ladder is intermediate in temperature and is a mix of pumped tailrace water and forebay surface water. Dark circles indicate location of temperature loggers and radiotelemetry antennas used to estimate ΔT. BO = Bonneville Dam, TD = The Dalles Dam, JD = John Day Dam, MN = McNary Dam.
Figure 2.
Mean daily water temperatures recorded at Ice Harbor Dam in 2000-2003.
Temperatures were monitored by the U.S. Army Corps of Engineers in the dam forebay at a depth of 5 m; similar data were collected at Lower Monumental, Little Goose, and Lower Granite dams. Black line = 2000, blue line = 2001, red line = 2002, green line = 2003.
Figure 3.
Mean daily ΔT estimates at six Snake River dam adult fish ladders in 2000-2003.
∆T was the water temperature difference between top-of-ladder and base-of-ladder monitoring sites inside fishways. S = South ladder, N = North ladder. Black line = 2000, blue line = 2001, red line = 2002, green line = 2003.
Figure 4.
ΔT encountered by Chinook salmon and steelhead at fish ladders and associated fish passage times.
Whisker plots show median, quartile, 5th and 95th percentiles. Years are sequential from 2000-2003, top to bottom, in each data cluster. Abbreviations as in Figure 1 except LGo = Little Goose Dam and LGr = Lower Granite Dam.
Figure 5.
Predicted time (d) Chinook salmon and steelhead use to pass Lower Granite ladder by ΔT.
Estimates were model-averaged means (± se) from annual GLMs for each run. Salmon and steelhead start time was held constant at 12:00 (noon). Base of ladder water temperature was held constant at 10° (open circles), 12° (gray circles), and 15°C (black circles) for spring Chinook salmon, 14° (open circles), 16° (gray circles), and 20°C (black circles) for summer Chinook salmon, 16° (open circles), 18° (gray circles), and 20°C (black circles) for fall Chinook salmon, and 13° (open circles), 17° (gray circles), and 20°C (black circles) for steelhead. These values were the 10th, 50th, and 90th percentiles of encountered temperatures for each run, rounded to the nearest degree. Note different y-axis scales.
Figure 6.
Chinook salmon and steelhead body temperatures in relation to ambient fish ladder water temperatures.
Data were collected in 2000 and 2002 at the time fish exited fish ladders (body temperature) and at the top-of-ladder monitoring site at Little Goose Dam (ambient temperatures). Linear regression results were: spring Chinook salmon (○), n = 128, F = 1378, P <0.001, r2 = 0.92, slope = 0.86, intercept = 2.71; summer Chinook salmon (Δ), n = 34, F = 231, P <0.001, r2 = 0.87, slope = 0.93, intercept = 1.52; fall Chinook salmon (●), n = 18, F = 155, P <0.001, r2 = 0.90, slope = 0.95, intercept = 1.14; summer steelhead (▼), n = 59, F = 856, P <0.001, r2 = 0.94, slope = 1.00, intercept = 0.94.