Stanislaus River - Escapement Monitoring Methods

Fall run Chinook salmon surveys are typically conducted on the Stanislaus River for three to four days per week from October through early January, with some annual variation depending on the number of returning salmon and environmental conditions. Surveys are conducted using a drift boat, kayaks, or on foot. Crew members will count all live fish and redds observed for each riffle while moving downstream.

Traditional mark-recapture methods were used to estimate fall run escapement on the Stanislaus River. Using these methods, carcasses are marked and subsequently recovered during weekly surveys of the spawning reach. A ratio of total fish handled to number of recoveries is used to calculate the total spawning population.

All visible carcasses are collected from each riffle and the pool immediately below. Each carcass handled is designated as fresh, decayed, skeleton, or recovery depending on the degree of decomposition or the presence of an aluminum jaw tag in the case of recoveries. Recoveries are recorded on the data sheet and returned to the river. Skeletons are in an advanced state of decay or have signs of predation and are enumerated and then chopped in half to avoid double counting in future surveys. Fresh and decayed carcasses are sampled to record sex, fork length, and adipose fin presence. A round disc tag is attached to the lower jaw as part of the mark-recapture study. Scales and otoliths are collected for age analysis. If no adipose fin is observed, the upper portion of the head is removed for later coded wire tag (CWT) extraction. CWT’s are analyzed to determine the hatchery of origin, release date and location, and fish age.