Solid numbers in for Napa River fish counters

By Guy Carl

A couple of months ago I shared a story about my experience as a volunteer counting steelhead trout in the Napa River.

This program, put together by the Napa County Resource Conservation District, was designed to measure the population of steelhead smolts as they migrate down-river and out to sea. A large rotary fish trap was purchased and installed in the river just north of the city of Napa this spring, during the height of the out-migration season.

This year’s out-migration season is now finished, and the trap results are in.

Jonathan Koehler, the RCD biologist in charge of the project, was extremely pleased with the numbers of fish found in the river.

He reports a total of 119 steelhead smolts were captured, counted and released during the two-month study.

To translate this figure into a measurement of the total population, several factors were taken into consideration. A little more than half of the smolts captured were marked and released upstream of the trap.

By measuring the number of these fish that were subsequently captured again, we can get an idea of what percentage of the total migrating population was actually caught by the trap.

Just one of these smolts was caught a second time, indicating that the trap was only capturing one to two percent of the river’s migrating smolts while it was in operation.

Another factor considered was that the trap could not be in operation throughout the entire migration season. In this first year of the program, the trap was not installed until late March when the smolt migration was already well underway.

Also, the heavy spring rainstorms raised the river flows too high for the trap to operate properly, so it was out of action for several more days. We can only guess how many smolts came through while the trap was out of commission.

Using all this information, and a little professional judgment, Koehler estimates between 10,000 and 20,000 Napa River steelhead smolts migrated to the ocean this year.

That’s pretty good for a federally-listed threatened species!

And prospects for the future look excellent as well. Nearly 1,000 frye and other juvenile steelhead were also captured in the trap during the study period. Many of these will be joining the migration over the next one to three years.

It’s important to note that several major tributaries were not included in the population count. The trap was placed upriver from the mouths of Milliken Creek, Tulocay Creek, Napa/Redwood Creek, and many others that flow directly into tidal waters.

These streams are known to host good steelhead runs, so the overall numbers of Napa River steelhead are substantially higher than Koehler’s calculated estimate.

To get a truer picture of the health of the river’s steelhead run, the study needs to continue for several more seasons.

Volunteers from the Napa River Steelhead organization were vital in helping with the daily monitoring of the trap this year, and similar volunteer efforts will be needed for future studies.

Foster’s Wine Estates was a huge part of the program, supplying equipment for installation, manpower and access through its property to the trap site on the river.

Funding is the other major requirement for this program to continue.

The RCD receives a small annual budget from Napa County to maintain its operations, but relies on grants and donations to run special projects like the Napa River steelhead study.

Anyone interested in donating to the 2010 study can contact Koehler at 252–4188 or jonathan@naparcd.org.

‘Rivers of a Lost Coast’ screening June 27

Another way to help the cause is by attending the movie screening of “Rivers of a Lost Coast” at the Napa Valley Museum in Yountville on Saturday, June 27.

This documentary reflects on the history of fly fishing in the rivers of Northern California over the last century, and the plight of their salmon and steelhead runs.

There is a reception at 7:30 p.m., where you can meet the film’s director, and the show begins at 8:30.

Tickets are $7 each and can be purchased at Sweeney’s Sports, or by calling the RCD at

252-4188, ext. 120.

Proceeds benefit the RCD and the Napa Valley Museum.

Guy Carl is a CPA and partner with BDCo Accountants and Advisors in St. Helena (www.bdcocpa.com).

Contact Guy at GC.outdoors@sbcglobal.net

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