Fall Chinook Salmon Run Characteristics and Escapement for the Main-Stem Klamath River, 2001-2010

Adult fall-run Chinook salmon (Oncorhynchus tshawytscha) carcasses were surveyed on the mid-Klamath River during spawning seasons 2001 through 2010 to estimate annual escapement using postmortem tag-recovery statistical methods and to characterize the age and sex compositions and spawning success of the runs. The study area consisted of eight consecutive reaches extending 21.2 river km from Iron Gate Dam downriver to the Shasta River confluence. A focus of this study was to improve what we believed to be negatively-biased estimates of escapement generated using redd counts. Unstratified Petersen carcass tag-recovery methods yielded 3.3 to 4.8 successfully spawned females per observed redd based on redd count data collected concurrently with carcass surveys. Based on Kimura-adjusted scale readings and unstratified Petersen escapement estimates, jacks (age-2 fish) represented less than 10% of the total annual escapement estimates for six of the ten survey years, with the greatest observed proportion of jacks occurring in 2006 (16%) and 2008 (17%). Low jack abundance in 2005 was indicative of low returns of age-3 adults in 2006 and age-4 adults in 2007 and similarly, low jack abundance in 2007 was indicative of low returns of age-3
adults in 2008 and age-4 adults in 2009. Despite low escapement estimates of adults in 2006, the abundance of jacks was relatively high, portending higher returns of 3-year old spawners in 2007 and 4-year old spawners in 2008. A similar pattern of low estimated escapement comprised of a relatively high abundance of jacks was observed in 2008, which was indicative of an abundance of 3-year old spawners in 2009 and 4-year old spawners in 2010. Pre-spawn mortalities of females ranged from about 22% in 2005 to 1% in 2009. Annual egg deposition by adult females calculated from unstratified Petersen estimates ranged from estimated highs of 24.5 and 25.0 million in 2002 and 2003, down to 5.7 and 4.7 million in 2006 and 2010.