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All salmon die after spawning so counting salmon carcasses is a valid method of population estimation. California Department of Fish and Game biologists float the Trinity River between Lewiston and Junction City weekly during spawning season. Salmon carcasses are checked for sex, length and whether or not they are tagged. A known number of fish are marked at CDFG weirs so a ratio of tagged to untagged fish yields an accurate population assessment of fall and spring Chinook salmon annually.