Klamath River near Salmon River confluence, California. (USFWS photo: G. Stutzer)

Automated radio telemetry receiver station on the lower Klamath River used to monitor fish passage. (USFWS photo: G. Stutzer)

FWS biologist surgically implanting a radio transmitter into a juvenile coho salmon in 2005. (USFWS photo: G. Stutzer)

by Gregory Stutzer, Arcata FWO
A study to estimate the effects of Iron Gate Dam discharge on ESA-listed juvenile coho salmon during their seaward migration to the ocean was begun in 2005.  Estimates of survival through various reaches of river downstream from the dam were completed in 2006, 2007, and 2008 as part of this process.  In each year a series of models were evaluated to determine apparent survival and recapture probabilities of radio-tagged fish in several river reaches between Iron Gate Hatchery at river kilometer 309 and a site at river kilometer 33.  The estimates of survival in 2008 were similar to those from 2006 and 2007 in reaches downstream from the Scott River.  The trend of lower survival in upper river reaches has been observed in each year of the study.  The survival of radio-tagged juvenile coho salmon in the Klamath River downstream from Iron Gate Dam in 2008 was slightly greater in hatchery-origin fish taken directly from a tank at Iron Gate Hatchery compared to those that were collected from a rotary screw trap in the Klamath River at rkm 293, though only 28 fish were in the latter group.  Survival probabilities from Iron Gate Hatchery to Steelhead Lodge were similar in 2007 (0.497 SE 0.044) and 2008 (0.538 SE 0.032; hatchery tank group), but were slightly lower than those from 2006 (0.653 SE 0.039).  The data from 2008 corroborate those from 2007.  The primary differences in survival estimates among the three years are due to a greater survival upstream from the Scott River in 2006.