Monitoring of Downstream Salmon and Steelhead at Federal Hydroelectric Facilities, 2005-2006 Annual Report.

Abstract

2005 was an average to below average flow year at John Day and Bonneville Dams. A large increase in flow in May improved migration conditions for that peak passage month. Spill was provided April through August and averaged about 30% and 48% of river flow at John Day and Bonneville Dams, respectively. Water temperature graphs were added this year that show slightly lower than average water temperature at John Day and slightly higher than average temperatures at Bonneville. The number of fish handled at John Day decreased from 412,797 in 2004 to 195,293 this year. Of the 195,293 fish, 120,586 (61.7%) were collected for researchers. Last year, 356,237 (86.3%) of the fish sampled were for researchers. This dramatic decline is the result of (1) fewer research fish needed (2) a smaller, lighter tag which allowed for tagging of smaller fish, and (3) a larger average size for subyearling chinook. These factors combined to reduce the average sample rate to 10.8%, about half of last year's rate of 18.5%. Passage timing at John Day was similar to previous years, but the pattern was distinguished by larger than average passage peaks for spring migrants, especially sockeye. The large spike in mid Maymore » for sockeye created a very short middle 80% passage duration of just 16 days. Other spring migrants also benefited from the large increase in flow in May. Descaling was lower than last year for all species except subyearling chinook and below the historical average for all species. Conversely, the incidence of about 90% of the other condition factors increased. Mortality, while up from last year for all species and higher than the historical average for all species except sockeye, continued to be low, less than 1% for all species. On 6 April a slide gate was left closed at John Day and 718 fish were killed. A gate position indicator light was installed to prevent reoccurrences. Also added this year was a PIT tag detector on the adult return-to-river flume. For the first time this year, we successfully held Pacific lamprey ammocetes. The number of fish sampled at Bonneville Dam was also down this year to 260,742, from 444,580 last year. Reasons for the decline are the same as stated above for John Day. Passage timing at Bonneville Dam was quite similar to previous years with one notable exception, sockeye. Sockeye passage was dominated by two large spikes in late May that greatly condensed the passage pattern, with the middle 80% passing Bonneville in just 18 days. Unlike John Day, passage for the rest of the species was well disbursed from late April through early June. Fish condition was good, with reductions in descaling rates for all species except unclipped steelhead and sockeye. Sockeye mortality matched last year's rate but was considerably lower for all other species. Rare species sampled at Bonneville this year included a bull trout and a eulachon.« less