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