Automated radiotelemetry receiver site at the confluence of the Salmon and Klamath Rivers. Photo:Greg Stutzer, 2007

By Greg Stutzer, Arcata FWO
Since 2005, the Fish and Wildlife Service has worked cooperatively with the U. S. Geological Survey, California Department of Fish and Game, Bureau of Reclamation, and the Karuk and Yurok Tribes of California to determine the extent that spring Iron Gate Dam (IGD) flow regimes affect survivorship of coho salmon smolts during their out-migration.  Survival and migration rates of wild and hatchery-origin radio-tagged juvenile coho salmon are estimated within five index flow reaches located between Iron Gate Hatchery (river kilometer 309) and the Klamath Estuary (river kilometer 13).  We use mark-recapture methods to estimate apparent survival, and time-to-event analysis with Cox’s proportional hazards regression to compare migration rates of hatchery and wild fish to gain insight on factors influencing survival and downstream travel times.

Results of migration analyses in 2006 were similar to those from the 2005 study.  In both years, we found longer travel times from release to the Scott River (rkm 233) than in reaches downstream.  During both years we found discharge to be a significant covariate of migration in this reach and not in others downstream.  The relations between day of the year, water temperature, fish length and travel rate were similar in the first two years of study, with each noting faster downstream travel as these variables increased.  The data from 2006 indicate there are differences between hatchery and wild fish migration behaviors in the upper two reaches (upstream from Indian Creek at rkm 178), but not thereafter.  Fish origin was a significant covariate of travel time through these reaches, with wild fish traveling faster than hatchery fish.

Current data and models indicate little support for a survival difference between hatchery and wild coho salmon in 2006, but considerable model uncertainty exists.  Survival was lower in the reach from Iron Gate Hatchery to the Scott River than in reaches located farther downstream.  The estimate of the overall survival from Iron Gate Hatchery to rkm 33 indicates survival through this section of the Klamath River in 2006 was similar to survival in other rivers.  The survival over this 276 km distance was 0.649, which equates to a survival of 0.855 per 100 km.  The current data suggest survival may not be constant through the various reaches of the Klamath River, but this approach is useful for purposes of comparison.

The 2006 report is currently in peer review and should be finalized and published in the near future.  Additional data were collected from 270 and these data are currently being finalized for analysis.  Our continued efforts to improve our understanding of the relationship between juvenile coho salmon survival and seaward migratory behavior relative to controlled river discharge should aid NOAA Fisheries in developing and implementing appropriate actions in recovery plans.