A recent survey indicates a sharp drop in the number of young steelhead trout swimming down the Napa River on their way to the ocean, a trend attributed to the ongoing drought.
Between March and June, biologists and volunteers with the Napa County Resource Conservation District tallied 31 steelhead smolts, the lowest number in six years since the annual count of the native fish began. The monitors this year also found no young Chinook salmon migrating to the ocean to mature.
As drought conditions persist, longer stretches of creeks and the Napa River dry up, forming barriers to the fish, according to wildlife officials. There is less water flow; creek habitats shrink.
“We are at the mercy of nature,” said Jonathan Koehler, senior biologist with the Resource Conservation District, as he explained this year’s low fish count. “I don’t know there is much we can do. I think it’s just documenting what’s happening.”
In 2009, the district monitors reported 119 steelhead trout caught in the rotary screw trap, an 8-foot-tall machine shaped like the nose cone of a spacecraft. In 2010, the biologists and volunteers who do the daily counts from February through June tallied 242 steelhead, the most in six years.
Three years later, however, when the current drought began, the number of steelhead smolts caught in the trap declined to 77.
“It will be really interesting next year, on the heels of three years of drought,” Koehler said.
Resource Conservation District biologists installed the rotary screw trap in 2009 to catch and count baby steelhead and Chinook salmon every spring at the same spot on the river. The goal was to obtain samples over a period of time and track trends, all in an effort to gauge the health of the Napa River watershed. The fish are counted, then measured before they are released.
The number of fish caught in the district's rotary screw trap, 1½ miles north of Napa, represents only an estimated 10 percent of the entire population for that spot.
Steelhead are the focus of the fish count because the species is considered an indicator of total fish life in the river. Steelheads need cold water and places to hide. If the habitat is good for the steelhead, the ecosystem is pretty healthy, Koehler said. “If you have a lot of steelhead, you generally have a lot of other fish, too.”
“It’s like the Dow Jones,” Koehler said, referring to the industrial average measuring the strength of the stock market.
Bernhard Krevet, president of Friends of the Napa River, a group that strives to protect the river, is aware of the low fish counts. “We are as concerned as everybody else,” he said. “The drought is obviously a factor.”
Wayne Ryan, an avid angler, has volunteered to monitor the rotary screw trap as a member of Napa River Steelhead, an organization that wants to preserve and conserve the native fish.
“It’s a setback for the fish populations in the river,” he said Saturday, referring to the drought and the low fish counts. “I hope it’s going to rain next winter.”