UPPER YOLO BYPASS — Rice fields have played a vital role in the revival of the Pacific Flyway, offering habitat for ducks, geese and shorebirds. Now, scientists believe the fields can play a role in bringing back the region’s beleaguered salmon population.

They envision the 59,000-acre Yolo Bypass — the main feature in the Sacramento flood control system — as a Chinook nursery.

On Tuesday, researchers deposited 50,000 two-inch-long, hatchery-raised salmon fry onto 20 harvested acres flooded about 14 inches deep here, between Interstate 5 and the Sacramento River.

In part, they hope to learn the optimal growing conditions for this new crop: when fields should be flooded and whether rice stubble, weeds or dirt makes the best flooded habitat.

Last year, a 5-acre research project here using 10,000 fish confirmed that salmon grow larger and stronger, feeding on the insects hatched when fields flood, than those in fast-moving river channels. Out there, the young fish find less food — and more predators.

In six weeks on the rice fields, the fish experienced a five-fold weight gain — among the largest in the region’s salmon research history.

“Floodplain fatties,” the thrilled scientists nicknamed them.

“If you’re big, your chances of survival when you go out to sea are much better and you’re much more likely to return,” said Peter Moyle, UC Davis professor of fish biology and principal investigator for the project.

As salmon go, farm fish are likely savvier, too.

“They’re learning how to behave like good wild salmon,” Moyle said. “The water’s full of life. There are birds overhead, so they have to learn to deal with predators. Everything about this is great.”

If this is new territory for researchers and farmers, it’s not for the salmon. They once thrived in the marshlands of the Sacramento Valley in much this way, before the arrival of manmade drains and levees. Just 5 percent of that seasonal marshland habitat now remains.

Current fisheries management isn’t doing the job, Moyle said.

“The hatcheries have worked, somewhat, but recent years have shown even they can’t prevent salmon decline,” he said.

Another 100,000 hatchery fish were released into the Sacramento River and into the Tule Canal, which runs alongside the bypass, as part of the research project. A small number of wild fish from the Feather River are being reared in the field, too.

Fish are painstakingly measured, weighed and tagged for comparison purposes.

Because they’re released at the same time and tend to behave in uniform ways, hatchery fish don’t fare as well as wild salmon, Moyle said, especially in years where food is not as abundant. Wild salmon head out to sea at different times and in different directions — they provide a more “diverse portfolio.”

A dramatic drop in adult salmon numbers — to 40,000 down from to normal levels of 100,000 to 200,000 — resulted in a fishing shutdown in 2008 and 2009, at a cost of $1.4 billion to the state’s economy by one estimate. This year, by contrast, looks like a banner one.

Jacob Katz, research project manager for California Trout, said he believes the salmon population can be brought back through better management.

“It’s not an inevitable result of development, these fish populations going down the drain. It’s that we’re not thinking about what drove the incredible productivity of California’s natural systems and then that unintentional alteration that’s led to the decline,” said Katz, a UCD doctoral student in fish ecology.

“But if you start to mimic those natural processes, if you start to mimic the drivers, in this case the flooding pattern — not the floods but the pattern — you end up with a system that can achieve everything we need of it.”

There is a precedent for such success.

While many farmers railed against a 1991 law that phased out the burning of rice stubble that once clouded the valley air, they found a new source of income outside of growing season in hunters eager for a shot at ducks drawn to flooded rice fields.

If the land is also managed for salmon, that could lead to subsidies to help pay for the higher infrastructure costs of farming bypass land that floods every two years out of three.

Under the Endangered Species Act, the state Department of Water Resources and U.S. Bureau of Reclamation are under orders to restore habitat 8,500 acres of floodplain habitat for salmon by 2016, to compensate for destroying or altering habitat in the Sacramento-San Joaquin Delta.

The university, nonprofit, landowners and local, state and federal agencies are all playing a role in the research project, setting the stage for the work ahead.

“I think you’re going to see ag becoming more and more involved in conservation, because of the cost-effectiveness of having ag in the mix,” said John Brennan, who manages the property for Knaggs Ranch LLC.

A bonus for rice growers, who’ve taken to calling their farms “surrogate wetlands”: Brennan thinks they will be able to market their rice as salmon-friendly. It’s a connection already enshrined in the name of the floodplain concept: “nigiri,” or sushi with raw fish served on rice.

What’s grown out here is tasty, too, Moyle said.

“It goes very well with salmon.”

— Reach Cory Golden at [email protected] or 530-747-8046. Follow him on Twitter at @cory_golden

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Baby salmon are measured, weighed and tagged Wednesday morning before being released into flooded rice fields northwest of Sacramento. Sue Cockrell/Enterprise photo

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Emma Cox releases baby salmon into enclosures in flooded rice fields northwest of Sacramento. Sue Cockrell/Enterprise photo

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Wildlife biologists Miranda Tilcock, left, and Nick Corline take samples of chlorophyl from water in the Yolo Bypass on Wednesday as part of a research project introducing hundreds of baby salmon in flooded rice fields northwest of Sacramento. Scientists are investigating whether the Central Valley’s river floodplains — long farmed for rice and other crops — could be managed to help recover California’s populations of Chinook salmon. Sue Cockrell/Enterprise photo

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