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Programs & DataConservation and ManagementCentral Valley MonitoringMerced River Escapement
Merced River Escapement Survey

  • Project Overview
  • Project Location
  • Methods
  • Contacts
Since 1954, the California Department of Fish and Wildlife (CDFW) has annually conducted an escapement survey to estimate the number of adult fall run Chinook salmon (Oncorhynchus tshawytscha) to return from the ocean and spawn in the Merced River. In the early years of the survey, scientists from CDFW’s Central Region estimated escapement using weekly live and redd observations made from atop bridges. In the 1980’s, they replaced this method with the Schaefer and pooled Petersen’s mark-recapture methods. Then in 2012, CDFW published a monitoring plan that standardized escapement methods across the state using the Cormack-Jolly-Seber (CJS) recapture method. Since 2013, CDFW’s La Grange Field Office has been using the CJS method to estimate the annual number of adult returns.

In addition to estimating the annual escapement, the objectives of the survey are:

  1. Collect data and analyze coded-wire tag data from hatchery-origin Chinook salmon.
  2. Collect sex and fork length data.
  3. Collect tissue samples for age and life-history reconstruction analyses.
  4. Collect data on redd distributions and redd formation timing.
  5. Escapement estimate and spawning data collected are used in evaluating the recovery of the species and fishery restoration in the basin.

The tranquil moment before a busy carcass survey day on the Merced River
A female Chinook salmon carcass.
Salmon carcass waiting to be processed.
CDFW staff carefully survey a riffle for salmon spawning on the Merced River.
CDFW staff extracting biological samples from a salmon carcass.
CDFW staff working together to collect carcass samples and data.
CDFW staff transverse through a rapid during the annual Merced River escapement survey.
Project Location

Merced River Escapement Map
Merced River Escapement Map

Merced River - Escapement Monitoring Methods


Beginning in the first week of October, 28-miles of the lower Merced River is surveyed by foot and drift boat by staff from the La Grange Field Office. This weekly survey starts at Crocker-Huffman Dam in Snelling, California and ends near Cressey, California.

Staff count live fish, redds and recover skeletons and carcasses at every spawning riffle. Whole carcasses, or carcasses in early stages of decomposition, are sexed, measured and sampled for scales, otolith (ear bones) and coded-wire tags. After sampling, these fish are tagged and returned to the river as part of the mark-recapture study. Skeletons and tagged recoveries in advanced stages of decomposition are chopped in half and returned to the river. The season typically ends in December or January after active spawning activities have reduced or ceased. At the end of the season, the data collected is ran through the Cormack-Jolly-Seber statistical model. The resulting estimate is combined with hatchery spawning data to give a total in river estimate that is used for commercial and recreational fishery management.


Contact Information

Vanessa Kollmar, Environmental Scientist
California Department of Fish and Wildlife
La Grange Field Office
PO Box 10 La Grange, CA 95329
Vanessa.kollmar@wildlife.ca.gov


Steve Tsao, Sr. Environmental Scientist
California Department of Fish and Wildlife
La Grange Field Office
PO Box 10 La Grange, CA 95329
steve.tsao@wildlife.ca.gov


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