Title: EFFECT OF THERMAL HISTORY ON THE RESISTANCE OF COLUMBIA RIVER STEELHEAD TROUT (SALMO GAIRDNERI) TO THERMAL STRESS.

Increased metal concentrations have been associated with freshwater acidification. Continuous-flow acute toxicity tests were conducted in soft water to determine the effect of pH on the toxicity of cadmium, copper, and zinc to small (1-6 g) steelhead trout (Salmo gairdneri). LC50 values were calculated for 96- and 168-h exposure periods in waters of pH 4.7, 5.7, and 7.0. Test fish were significantly more tolerant of the metals at the lowest pH value than at higher pHs. The 96-h LC50 values at pH 4.7, 5.7, and 7.0 were 671, 97, and 66 micrograms/L for zinc, 66.0, 4.2 and 2.8 micrograms/L formore » copper, and 28.0, 0.7 and less than 0.5 micrograms/L for cadmium, respectively. The 168-h results were similar to the 96-h values. The results indicate that for the metals tested, toxicity is ameliorated in depressed pH waters over short exposure periods, such as may occur during snowmelt runoff. The possibility of hydrogen-ion interference with metal uptake is postulated.« less

The steelhead is an anadromous form of the rainbow trout Salmo gairdneri found from central California to Alaska. The commercial fishery in the Pacific Northwest is restricted to specific Indian tribes. Washington and Oregon support an important recreational fishery. In Washington and Oregon, two runs of steelhead exist. Winter-run steelhead enter their native streams in late fall and winter, and usually spawn by the following May. Summer-run steelhead return to their home streams in spring and summer, and usually spawn in the following spring. California stocks apparently consist only of winter-run fish. Female steelhead bury their eggs in gravel inmore » streams after spawning. Proper temperature and dissolved oxygen levels are necessary for incubation of eggs and rearing in streams. Adequate particle size of stream gravel and adequate stream velocity are essential for incubation.« less

Program RealTime provided tracking and forecasting of the 1999 inseason outmigration via the internet for stocks of wild PIT-tagged spring/summer chinook salmon. These stocks were ESUs from sixteen release sites above Lower Granite dam, including Bear Valley Creek, Big Creek, Cape Horn Creek, Catherine Creek, Elk Creek, Herd Creek, Imnaha River, Lake Creek, Loon Creek, Lostine River, Marsh Creek, Minam River, South Fork Salmon River, and Secesh River, Sulfur Creek and Valley Creek. Forecasts were also provided for a stock of hatchery-reared PIT-tagged summer-run sockeye salmon from Redfish Lake and for the runs-at-large of Snake River wild yearling chinook salmon,more » and steelhead trout. The 1999 RealTime project began making forecasts for a new stock of PIT-tagged wild fall subyearling chinook salmon, as a substitute for forecasts of the wild run-at-large, discontinued June 6. Forecasts for the run-at-large were discontinued when a large release of unmarked hatchery fish into the Snake River made identification of wild fish impossible. The 1999 Program RealTime performance was comparable to its performance in previous years with respect to the run-at-large of yearling chinook salmon (whole season MAD=3.7%), and the run of hatchery-reared Redfish Lake sockeye salmon (whole season MAD=6.7%). Season-wide performance of program RealTime predictions for wild Snake River yearling chinook salmon ESUs improved in 1999, with mean MADs from the first half of the outmigrations down from 15.1% in 1998 to 4.5% in 1999. RealTime performance was somewhat worse for the run-at-large of steelhead trout in 1999, compared to 1998, particularly during the last half of the outmigration when the MAD increased from 2.7% in 1998 to 6.1% in 1999. A pattern of over-predictions was observed in half of the yearling chinook salmon ESUs and the steelhead run-at-large during the month of May. Lower-than-average outflows were observed at Lower Granite dam during the first half of May, the only period of low flows in an year with otherwise higher-than-average-flows. The passage distribution of the stock new to the RealTime forecasting project, the PIT tagged stock of fall subyearling chinook salmon, was predicted with very good accuracy (whole season MAD=4.7%), particularly during the last half of the outmigration (MAD=3.6%). The RealTime project reverted to a pre-1998 method of adjusting PIT-tagged smolt counts at Lower Granite Dam because of its superior performance during the last half of the outmigration.« less