Fewer chinook salmon returned to spawn in the Napa River this season, a fact that Napa County biologists think may be linked to poor ocean conditions.

Smaller salmon runs were reported in other watersheds in the region as well, noted RCD biologists who surveyed a stretch of the Napa River in December and January.

Jonathan Koehler, a senior biologist at RCD, said these results point to poor ocean conditions, including shifts in the amount of plankton available to fish and shrimp for the salmon.

The waters where the counts are low have one thing in common — the ocean, he said. “All our fish go out to the ocean.”

To do the survey, RCD biologists counted salmon nests or redds — areas in the bottom of the river the fish clear with its tail to spawn — from St. Helena to north Napa.

Counting redds is more accurate than counting fish, because adult fish can easily be double counted, the RCD biologists explained during a recent presentation of their findings.

The biologists found nine redds per kilometer — or more than four fewer than in 2005 and 2006 along the 4.5-mile stretch between Oakville Crossing and St. Helena, where most redds are found.

Koehler stressed more counts will have to be done to establish long-term trends. It is only the fourth year that data has been collected on the chinook salmon spawning season in the Napa River, where an estimated 400 to 600 adults live.

In the Central Valley, the number of chinook salmon returning to the Sacramento River this fall was a record low, a particularly distressing result, according to the Pacific Fishery Management Council, a group that proposes salmon fishing rules to federal officials every spring along the Pacific Coast.

Chuck Tracy, a salmon staff officer for the Pacific Fishery Management Council, on Friday said a low salmon run in the Napa River is reflective of what is going on up and down the Pacific Coast.

“It does look like there is a coastwide trend,” said Tracy, whose organization studies data from major watersheds in California, Oregon and Washington State. However, the reasons are unclear.

“We don’t know for sure” why this is happening, said Tracy, who explained the lower count may lead to a shorter commercial salmon season this year.

Chinook salmon return to the Napa River at age 2-5 years to spawn and die.

Chris Malan, a Napa environmentalist, said she is not surprised at this year’s low chinook salmon count. She saw hundreds of dead juvenile chinook salmon this summer in isolated warm pools while kayaking, she said.

The river’s health suffers from various factors, including poor water flows, increased temperature and severely eroding banks along the river, she explained.

The Napa River has been declared an impaired river under the federal Clean Water Act. State water quality regulators are scheduled to review this spring a plan to restore the Napa River watershed.

RCD biologists also collected 70 DNA samples from carcasses which they shipped to the National Oceanic and Atmospheric Administration in Santa Cruz to find out if they came from other watersheds. The studies could determine if fish from hatcheries have been able to establish themselves in the Napa River, explained Koehler.