Denise Barnard and David Dominguez of the STFWO sample tissue from the caudal fin of a juvenile Chinook salmon. - Photo Credit: USFWS

Tissue sample taken from a juvenile Chinook salmon. - Photo Credit: USFWS

By Denise Barnard, Stockton FWO

July 2011 marked the end of a 4-year sampling project using genetic tools to more accurately define the races or runs of winter, spring, fall, and late fall Chinook salmon in the Sacramento and San Joaquin Rivers. Winter run salmon are listed as endangered under the Endangered Species Act (ESA), while spring run salmon are listed as threatened. Improving race designations may influence ESA take allotments and improve estimates of respective populations in sampled areas.

Races are currently designated by the Stockton Fish and Wildlife Office (STFWO) using the "River Model," a technique developed by Frank Fisher of the California Department of Fish and Game (DFG) in 1992. Fisher’s method uses observed spawning times and fall run growth rates to predict when juvenile salmon of each race should appear in the Sacramento River and Delta at a given size. While this model is known to have some limitations, it is the only tool available to differentiate juveniles by race in the field and is widely used.

The genetics project was headed by STFWO biologist Patricia Brandes. Field crew from the STFWO, with funding from the Interagency Ecological Program, took tissue samples from Chinook salmon caught during regular trawl sampling in the Suisun Bay and Sacramento River near Sherwood Harbor. Tissue samples were taken from the caudal fin of unmarked salmon (e.g., salmon which were not adipose fin clipped in a hatchery). In addition, we hope to explore the possibility of determining salmon race by analyzing scales, so two scale samples also were taken from each tissue-sampled fish in anticipation of later analysis.

Roughly 4,300 salmon were sampled in 2011, producing 4,300 tissue and 8600 scale samples. These tissue samples were sent to the DFG Tissue Archive Lab in Sacramento prior to being sent to the lab of Dr. Michael Banks, of Oregon State University.  Banks’ team will analyze specific DNA markers called microsatellites to predict the race of each sampled salmon.

This project could improve our ability to determine salmon races while sampling, greatly expanding our knowledge of Chinook salmon life history in the Delta.