A marking, tagging, and recovery program for Central Valley hatchery chinook salmon
A second analysis

Allan Hicks

Ken Newman
Dave Hankin

March 30, 2005

---

EXECUTIVE SUMMARY

These are new simulationsof the Central Valley chinook salmon marking program in addition to the simulations reported by Newman et al (2004) .These simulations differ in the following ways.

1. No Surrogate fish were released but CFM marked fish were used as surrogates for wild stocks,
2. The freshwater harvest rate for the Sacramento River was increased to be the same as the American and Feather rivers,
3. The catch sampling rates (CSR) considered were 5%, 15%, and 25%,
4. The escapement sampling rates (ESR) were 5%, 10%, or 20% for the American and Feather Rivers and 30%, 45%, and 60% for all other watersheds.

We extended statistical procedures that we had previously developed for estimating the production of wild and hatchery chinook salmon in the Central Valley. Corresponding enhancements were also made to a computer program called CFM Sim which simulates marking, tagging, sampling, and production estimation procedures. Using CFM Sim and a factorial experiment design, we evaluated the effects of varying four man-controlled factors on the quality of estimates of wild and hatchery chinook salmon production.

The four man-controlled factors were:

1. Constant Fractional Marking (CFM) rate (f): the percentage of production releases at a given hatchery that received a coded-wire-tag and an adipose fin clip,
2. Catch sampling rate (CSR): the fraction of ocean and freshwater salmon catch being sampled,
3. Escapement sampling rate (ESR): the fraction of in-river escapement being sampled, and
4. Coefficient of variation of escapement estimates (ECV).

Our recommendations given below, regarding constant fractional marking levels and some of the other manipulable factors, are of a general, relative nature.

General recommendations:

1. Implement a system-wide constant fractional marking program for Central Valley hatchery reared salmon. The recommended constant fractional marking rate for production releases from all hatcheries is at least 1/3 or 33%. Increasing the CFM rate beyond 33% would result in minor gains..
2. Calculate measures of the precision and bias of watershed-specific wild salmon escapement estimates. This means at a minimum calculating standard errors to accompany the point estimates for each watershed (and race, e.g., fall-run, late fall-run, winter run). For one or more watersheds, or portions of watersheds, carry out an estimation procedure which can serve as a benchmark for assessing the accuracy of existing escapement estimation procedures. This could mean installing temporary weirs on smaller streams, for example, which would allow counts of returning spawners to be made in conjunction with implementation of current sampling and estimation procedures on the same streams.
3. Implement a consistent system-wide freshwater catch sampling program and develop, if not already available, corresponding estimation procedures. Standard errors should be calculated along with point estimates of total catches and catches of particular wild and hatchery stocks.
4. In order to evaluate how well a hatchery release group, chosen as a surrogate stock for a wild stock, actually represents the wild stock (in terms of age 3 and older survival rates, harvest rates, and maturation rates, in particular), mark and tag for multiple years, on multiple watersheds outmigrating wild juvenile salmon. Compare the tag recovery patterns for these tagged wild fish with those of the surrogate hatchery fish. It is very important that the surrogate releases (CFM marked fish in this analysis) closely mimic the wild fish that they represent.