Tuolumne River - Escapement Monitoring Methods

Fall run Chinook salmon escapement surveys on the Tuolumne River typically begin around the first week of October and extend into the end of December or early January. The study area is surveyed weekly to monitor the distribution of spawning and to record the number of carcasses found within the river. Crew members float downstream in a drift boat searching for and collecting carcasses, counting live salmon and documenting redds in each riffle and subsequent pool. The standard way of estimating salmon populations in the Tuolumne River is by mark-recapture survey.

All salmon carcasses collected, and their condition is recorded as fresh, decayed, skeleton or recapture. The fresh and decayed carcasses have sex and fork length recorded, along with the retrieval of scales and otolith samples. All carcasses, regardless of condition, are checked for a clipped adipose fin, which indicate hatchery origin. Any adipose clipped fish have their head removed for extracting the coded-wire tag. Coded wire tags are analyzed by microscope to determine original hatchery location, fish age, release location and date released. Fresh and decayed carcasses are tagged with a unique number and returned to the river for recapture in future weeks. Skeletons are tallied and chopped after checking for an adipose clip, preventing them from being double counted or recovered in future surveys. Recaptured fish from previous weeks are recorded by unique number and are returned to the river to be recaptured multiple times. Once a recaptured fish is in advanced decomposition stage or predated upon it is recorded and chopped.