This report describes a study of survival and migration behavior of radio-tagged juvenile coho salmon (Oncorhynchus kisutch) in the Klamath River, northern California, in 2007. This was the third year of a multi-year study with the goal of determining the effects of discharge at Iron Gate Dam (IGD) on survival of juvenile coho salmon downstream. Survival and factors affecting survival were estimated in 2006 and 2007 after work in 2005 showed radio telemetry could be used effectively. The study has included collaborative efforts among U.S. Geological Survey (USGS), U.S. Fish and Wildlife Service (USFWS), the Karuk and Yurok Tribal Fisheries Departments, and the U.S. Bureau of Reclamation. The objectives of the study included: (1) estimating the survival of wild and hatchery juvenile coho salmon in the Klamath River downstream of Iron Gate Dam, determining the effects of discharge and other covariates on juvenile coho salmon survival (2) and migration (3), and (4) determining if fish from Iron Gate Hatchery (IGH) could be used as surrogates for the limited source of wild fish.
We have been able to meet the first objective by estimating the survivals of hatchery and wild fish (when available) downstream of IGD. We have not yet met the second or third objectives, because we have been unable to separate effects of discharge from other environmental variables as they pertain to the survival or migration of juvenile coho salmon. This was foreseen when the study began, as it was known there would likely be no experimental discharges. A multi-year analysis will be conducted after the data for the third planned year are available. The fourth objective was initiated in 2006, but wild fish were not available in 2007. The next year wild fish may be available is in 2009, based on their 3-year cycle of abundance.
River discharges during the 2007 study period (April 10 through July 28, 2007) were below average compared to the period of record beginning in 1962. Average daily discharge at IGD was 1,518 cubic feet per second (ft3/s) and ranged from 1,020 to 2,460 ft3/s. Average daily discharge near the estuary at river kilometer (rkm) 13 was 9,820 ft3/s and ranged from 3,270 to 20,500 ft3/s.
This study was based on hatchery fish taken directly from a holding tank at IGH. Wild fish were not available in numbers sufficient for use in 2007. Fish tagging began on April 9 and concluded on May 17, 2007. A total of 246 hatchery coho salmon were tagged and released, split evenly between releases in the Klamath River near IGH (rkm 309) and near the Tree of Heaven campground at rkm 280.
The two release sites were used to enable estimation of a relative survival between IGH and the campground using the paired-release design, because potential effects of tagging and handling can be cancelled out with this method. However, the assumption that the survival probabilities of fish from each release site are equal in the reaches they have in common was violated, preventing its use in 2007. All estimates of survival were therefore calculated using the single-release design.
The reach-specific estimates of survival were lower in 2007 than in 2006, but a similar survival pattern was evident among reaches in each year. The survival from IGH to rkm 33 was 0.653 [standard error (SE) 0.039] in 2006 and 0.497 (SE 0.044) in 2007. In each year, the reaches with the lowest survivals were upstream of the Scott River, which also is the area with the greatest differences in survivals between years. The reach with the highest survivals were in the Salmon River-to-Trinity River reach (at or near 1.0 in each year). The cause of the difference in survivals in each year were not identified, but could be related to differences in discharge or turbidity, as these are the primary differences between the years. These differences and other effects will be analyzed when the data from all study years (initially planned for 2006 through 2008) are available. Models of su
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USGS Numbered Series
Survival and migration behavior of juvenile Coho Salmon in the Klamath River relative to discharge at Iron Gate Dam, Northern California, 2007