Taking a count of Napa River’s marine life

Rotary trap keeps track of local species

By Guy Carl
Outdoors

Have you ever wondered what swims in the waters of our Napa River? I had the opportunity this week to observe a sampling of fish, amphibians, and even some crustaceans that call the river home.

A program designed to measure the Napa River system’s steelhead population has been put together this spring by the Napa County Resource Conservation District (RCD).

A large rotary fish trap was installed in the river earlier this year just north of the city of Napa, upstream from any influence of the bay’s salt water.

The volunteer group, Napa River Steelhead (NRS), has signed on to help RCD personnel with the daily counting and monitoring of the fish trap.

This is how I, along with many other volunteers, became involved in the process of gauging the health of our native steelhead run.

The trap is set up so that, as the steelhead smolts migrate downstream towards the ocean, a percentage will be captured and safely held until personnel arrive. Each morning, these smolts are to be counted, measured, weighed, and released back into the river to continue their journey.

On my day to help this week, RCD biologist Jonathan Koehler was in charge of the counts. Joined by my wife, Julie, and fellow NRS volunteer John Nogue, we hiked down the bank to the contraption floating in the river.

The trap’s holding tank had a healthy variety of marine life for us to count. It was a particularly good day as we were excited to find six steelhead smolts in the mix! They were all seven to eight inches long, and four of these had taken on the silvery sheen of a migrating fish. The other two still had the colorful rainbow trout markings of a resident fish, either not yet old enough to leave the river or perhaps a permanent resident.

The smolts are generally two to three years old when they become ready for the migration. They lose their distinctive trout markings and become more silvery, similar to a salmon. Their genetics are telling them it’s time to leave their home in the river and make a new home in the ocean.

According to Jonathan, smolts that reach 18 centimeters long (about 7 inches) before migrating stand an excellent chance of reaching the ocean. Anything smaller stands an excellent chance of becoming lunch for a hungry striper in the river’s lower reaches or the bay.

Before release, a very small clip of a fin is taken to mark the fish as having been counted, in case it finds its way back into the trap again before heading out to sea.

A small sample of each fish’s scales is also taken for genetic analysis and to determine the fish’s age.

To protect the smolts from injury, they are sedated during the measuring process.

After all appropriate documentation and samples are complete, the fish are revived and released back into the river unharmed.

In addition to the steelhead smolts, we also found in the trap several river lamprey (about six inches long), a bunch of minnows called “roach,” a number of sculpin, a few crawdads, and a very large bullfrog with a couple of tadpoles.

There was also one other exciting find, a tiny fry that Jonathan believed was a recently-hatched Chinook salmon!

The salmon have been returning to the river in recent years, and it appears they have been successfully spawning.

This fry was estimated at about one month old.

Other kinds of fish caught in the trap this year have included bass, crappie, suckerfish, pikeminnow, and stickleback minnow.

It’s a lot of fun and very educational to learn what kinds of fish and other creatures live in our local river.

And it’s a great feeling to know that the data gathered will help us properly manage the native steelhead population, and ensure its sustainability for generations to come.

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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