Project: Caspian tern predation on Upper Columbia River steelhead: Retrospective analysis of juvenile salmonid acoustic telemetry systems (JSATS) data
Client: Grant County PUD
Year: 2012 - 2015
Location: Columbia River PlateauA spatial and temporal retrospective data analysis of JSATS-tagged salmonids was conducted to evaluate total mortality relative to mortality caused by piscivorous waterbirds in the Wanapum and Priest Rapids Project (dam and reservoir) in the middle Columbia River. Results were used to identify both the locations and magnitude of smolt losses due to avian predation. Geospatial maps and mark–recapture modeling techniques were used to generate results.
Results demonstrated that Caspian tern predation was a substantial source of fish mortality, with terns nesting on Goose Island in Potholes Reservoir annually consuming between 13% and 21% of juvenile steelhead released into the tailrace of Rock Island Dam during 2008-2010, with the majority of this predation occurring within the Wanapum-Priest Rapids Project. Reservoir‐specific predation rates ranged from a low 4.0% in the Priest Rapids Reservoir in 2010 to a high of 10.0% in the Wanapum Reservoir in 2009. A positive association between the size of the Goose Island Caspian tern colony and steelhead predation rates was observed, with predation rates increasing with an increase in tern abundance (number of adults) on the Goose Island colony.
Comparisons between survival rates and predation rates indicated that a substantial proportion of steelhead mortality within the Priest Rapids Project can be attributed to predation by Caspian terns nesting on Goose Island in Potholes Reservoir. Overall, an estimated 49%, 85%, and 37% of all steelhead mortality in the Priest Rapids Project during 2008, 2009, and 2010, respectively, could be attributed to predation by Caspian terns nesting on Goose Island.
Project was conducted in cooperation with Blue Leaf Environmental and involved close coordination with Grant County PUD and Oregon State University.