The LAR escapement survey is conducted annually from mid-October through mid-January. A 13-mile section of the LAR from the Nimbus weir (near Hazel Avenue) to Watt Avenue is surveyed once per week for salmon carcasses.
A standard technique employed in California for estimating salmon population size is the mark-recapture survey. This technique consists of weekly surveys of a section of river conducted over the entire spawning period.
During each survey, the freshest carcasses are externally marked with a unique number and returned to the water near the spot encountered. Data obtained from the recapture of marked carcasses are used to estimate the size of the spawning population. Badly decomposed carcasses are tallied and chopped in half to avoid being counted on subsequent surveys.
Covariate data, such as sex, length, presence or absence of adipose fin, and degree of female egg retention are recorded. Heads are collected from hatchery fish in order to extract coded wire tags which indicate the salmon’s age, hatchery origin, and site and date of release.
Lower American River Fall-run Chinook Salmon Escapement Survey Reach Map
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