While rain was falling outside, the conversation inside the Napa Bookmine Wednesday night was of decidedly drier concerns — the state of the Napa River’s fisheries during California’s prolonged drought.
Napa County Resource Conservation District biologist Jonathan Koehler led a discussion of the impacts the dry weather could have on fish in the river, and how they may be handling these conditions.
The species most residents associate with the middle to upper Napa River — which is the stretch most affected by the drought — are Chinook salmon and steelhead, but Koehler said the river also hosts several kinds of minnow, suckers, lamprey and trout, among others.
The river has a series of tributaries from both the west and east side of the Napa Valley, many of which have been dry, Koehler said. That’s not uncommon — even in years with normal or above average rainfall, he said.
The migratory and non-migratory fish can survive in deep pools in these tributaries for months until the rain returns, he said.
Koehler said Chinook salmon have adapted to drought conditions by returning to spawn at different times — some may return in one year, while others will spend another two years or more at sea.
That’s a natural check against drought, because once the fish return they either have to spawn and die or die without spawning, he said. Their spawning produces large numbers of offspring that travel down the river when the juveniles are relatively small, making them easy prey, Koehler said. But the large numbers help ensure more make it to salt water and the ocean.
Steelhead, on the other hand, spawn in the higher reaches of the river and its tributaries, and wait several years before migrating down. Steelhead can return to salt water once they’ve made it back to the river, if the conditions aren’t suitable for spawning.
Koehler said the Napa River requires at least six inches of rain to acquire a suitable flow for migratory fish.
“That never happened this year,” Koehler said. “We have a big, thirsty valley.”
Steelhead are genetically identical to rainbow trout, but steelhead migrate to the ocean, Koehler said. Some may remain in the river as trout, ensuring the species continues to reproduce, he said.
The river can also be home to some types of lamprey, although that requires multiple years of wet conditions, which hasn’t happened in the Napa River, he said.
The minnows and suckers also call the middle portion of the Napa River home, but that flat stretch of water is also the most vulnerable to drying up in drought conditions. Without water in the channel, those fish have few options, he said.
“In a drought, it’s another species that really doesn’t have a Plan B,” Koehler said.
Koehler ended his talk on a cautionary note, and said a college professor of his, Scott Stine of the University of California, Hayward, had studied trees rooted in 70 feet of water in lakes in the Sierra Nevada.
Stine’s conclusion, upon extensive study, was that those trees had rooted and grown when the water level was extremely low, the product of decades-long droughts. He concluded the state experienced drought-like conditions, with some rainfall but not much, for 100-year and 140-year periods in between 1100 and 1500 A.D.
“It’s been a really wet 150 years,” Koehler said. “We’re running out of water in the best of times.”