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Title: Predation Susceptibility of Juvenile Fall Chinook Salmon Exposed to Sudden Temperature Changes and Slightly Supersaturated Dissolved Gas

High mortality of hatchery-reared juvenile fall Chinook salmon emigrating from the Clearwater River was previously measured at the confluence of the Snake and Clearwater rivers; however, the causative mechanism of mortality is unknown. To elucidate potential mechanisms, the predation susceptibility of juvenile fall Chinook salmon was assessed during simulated passage from the Clearwater River and through the confluence of the Clearwater and Snake rivers, with and without cool water flow augmentation. Emigrant-sized juvenile salmon were acclimated to temperatures typical of the Clearwater River when cool water augmentation is discharged from Dworshak Dam (10°C to 17°C) and during temperatures that would be present without augmentation (17°C to 24°C), and were then exposed to smallmouth bass within temperatures typical of the Snake River in summer (17°C to 24°C). Slightly supersaturated total dissolved gas concentrations of 105% were also simulated to more closely approximate gas conditions of both rivers in summer. Predation susceptibility of juvenile salmon acclimated at 10°C or 17°C and exposed to predators at 17°C did not differ. However, for salmon exposed to predators at 24°C, predation susceptibility was arguably higher for juvenile salmon acclimated at 10°C (a 14°C increase) than for salmon acclimated at 17°C or 24°C (7°C and 0°Cmore » increases, respectively). These results indicate that predation susceptibility may be higher when a relatively large temperature difference exists between the Clearwater and Snake rivers; that is, when cool water flow augmentation is occurs in summer. However, further research is needed to determine if high confluence mortality measured in previous studies is related to cool water augmentation and, ultimately, whether or not this mortality has a population-level effect on the dynamics of wild Snake River fall Chinook salmon.« less
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Related Information: Snake River Fall Chinook Salmon Life History Investigations, 1/1/2012 - 12/31/2012 Annual Report, 2002-032-00:61-90
KF Tiffan, et al; Bonneville Power Administration , Pasco, WA, United States(US).
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
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Country of Publication:
United States
Oncorhynchus tshawytscha; fall Chinook salmon; temperature change; flow augmentation; predation susceptibility