Date of Award
Master of Science (MS) in Biology
"The object of this study was to quantify consumption rates of juvenile salmonids by three introduced species, smallmouth bass (Micropterus dolomieu), walleye (Sander vitreus) and channel catfish (Ictalurus punctatus). Consumption information is crucial because the construction of the Snake River hydrosystem has created a series of reservoirs, which have altered the river 's flow regimes, riparian vegetation, and turbidity. Further, several non-native fishes have been introduced as sport fish into the Lower Snake River. This combination of physical alterations and new biological interactions with introduced species has reduced the survival of anadromous salmonids in the Lower Snake River. Currently all Snake river salmonids are listed as threatened or endangered under the Endangered Species Act. A series of 12 sites, in four Lower Snake River reservoirs, were sampled via nighttime electrofishing in the spring and summer of 2011. All fish captured were identified, measured (mm) and weighed (g). Relative abundance of smallmouth bass was 4.6%, walleye 0.13% and channel catfish 0.08%. By weight, salmonids comprised 2% (smallmouth bass), 32% (channel catfish), and 0% (walleye) of the predator diet. The ability of smallmouth bass to consume juvenile salmonid prey was investigated in vitro, using four turbidity levels (0, 0.5, 5 and 10 NTUs), and five prey densities (1,2,4,8,16 prey items). In trials with 16 prey items, predation was significantly lower in treatments with 5 or 10 NTU than trials with 0.5 or 0 NTU, suggesting that under high prey densities, turbidity may reduce with smallmouth bass feeding predation. Flows and turbidity were high during the entirety of field sampling, which likely reduced the incidence of salmonids in predator stomachs. Reduced predator metabolic rate (due to lowered temperatures), and turbidity are associated with high flows. Future management efforts may include maintaining turbidity in the water column, along with spring and summer flow augmentation as a way to enhance juvenile salmonid survival during outmigration to the ocean"--Document.
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Sontag, Devin M., "Predation, turbidity, and other factors influencing juvenile Salmonid survival in the lower Snake River" (2013). EWU Masters Thesis Collection. 168.