PNNL

Abstract

Two alternative release-recapture methods were used to estimate dam passage survival of juvenile salmonids through Lower Granite Dam in the Snake River, Washington State in 2018. One approach, the ViPRE model, has been extensively used in the Columbia/Snake River Basin at federally operated hydroelectric dams, 2010–2014. This existing approach uses three releases of tagged smolts to isolate dam passage survival, defined as survival from the upstream dam face to the tailrace mixing zone, 1 km to 2 km downstream of the dam. An alternative approach, the ViRDCt model, uses one alive release paired with a release of dead-tagged fish at the dam to estimate the same survival parameter. The alternative estimation approaches were tested on two spring migration stocks, yearling Chinook salmon and steelhead, and on a summer migrant stock of subyearling Chinook salmon. The alternative estimates for these stocks were all within one standard error. However, the ViRDCt model produced survival estimates with standard errors 58% smaller than those of the existing ViPRE model, and did so, using 42% less fish and one less downstream acoustic detection array.