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Baby Salmon Thrive in California Rice Fields

Baby Salmon Thrive in California Rice Fields

When Steve Neader’s rice farm flooded last winter after three years of drought, a UC Davis research team checked to see what else had come in with the water. Neader grows rice in California’s Sutter Bypass, a huge leveed channel north of the city of Sacramento that ultimately shunts river overflows into the Sacramento-San Joaquin River Delta.

The team was looking for fish. “I saw the researchers on my way to lunch and when they told me what they were doing, I just laughed,” Neader recalls.

But when he came back from lunch, the researchers had just netted a foot-long largemouth bass. They also found plenty of other fish, including those they most wanted to see: Chinook salmon. As many as a couple of million adult Central Valley chinook once returned from the ocean to spawn in rivers and streams each year, but these fish are now imperiled by the many dams and levees that cut them off from their best spawning and nursery habitat.

The researchers were on Neader’s farm to optimize rearing baby salmon in rice fields, a five-year effort spearheaded by California Rice Commission Environmental Affairs Manager Paul Butter. He helped establish a similar program that pays Central Valley rice growers to manage their fields for water birds migrating along the Pacific Flyway.

Now he wants to do the same thing for young salmon migrating from the Central Valley to the ocean, where the fish spend most of their adult lives. This year the project was wildly successful.

“It’s the first time we’ve done the practice on a full-size rice field and had natural-origin fish on the field,” Buttner says. “We’re excited!”

MIMICKING FLOODPLAINS

Central Valley salmon migrating toward the ocean once grew up in vast river floodplains. Today most of California’s rivers are leveed and 95% of the floodplains are gone. But the state does have the next best thing: enormous flood control bypasses that drain into the Delta, which in turn drains into the Pacific Ocean.
Sutter Bypass rice field flooded to a depth of one foot for baby salmon. Photo courtesy of California Rice Commission.

“This is a unique system,” says UC Davis fish expert Andrew Rypel, who leads the science side of the salmon rearing project. “We’re fortunate to have it in California.”

The Sutter Bypass, where Neader’s farm is, feeds into the Yolo Bypass. These two flood control structures contain 15,000 acres that are farmed for rice in the spring and summer growing season—and could double as salmon nurseries in the winter.

Rice fields are surprisingly well-suited to salmon rearing. The bypasses were engineered to drain, so floodwaters recede relatively quickly. In contrast, rice fields are surrounded by berms to keep water in. And all told, California has about half a million acres of rice fields where baby salmon could thrive.

“Fish and farmers are pitted against each other in California but these kinds of partnerships are the only way forward,” Rypel says. “There’s just not enough wetlands without them.”

FISH ON FIELDS
Tagging a young rice-field reared salmon for tracking to the ocean. Photo by Brian Baer.

Like natural floodplains, winter-flooded rice fields are slow, shallow, and teeming with zooplankton, tiny creatures that little fish gobble down. Key elements in substituting rice fields for floodplains include inundation well in advance to build up a nourishing zooplankton soup for hungry young salmon, and ensuring that salmon can swim throughout a field.

The latter is critical to state and federal fish and wildlife agency approval. Confining endangered species is illegal, and two of the four Central Valley chinook salmon runs (winter and spring) are listed under the federal Endangered Species Act. The remaining two runs (fall and late fall) are federal Species of Concern.

Today most baby chinook migrate downstream in the winter. This year, water from the Sacramento River poured into Neader’s land in early January, making it a perfect test of managing rice fields as salmon nurseries. “Everything was out there—we had all four runs of salmon, steelhead and many other fish,” Rypel says. “It was amazing.”
Rice field managed for salmon born in the wild. Figure courtesy of California Rice Commission.

The 125-acre test rice field had an estimated 4,000 baby chinook. Growers divide rice fields into sections separated by wooden boards, which act as small dams to regulate water depth and movement. To let the little fish go wherever they wanted, the research team modified the boards by drilling a small hole or two through each one and cutting a small notch at the top. These modified boards were then placed between field sections as well as at the exit to the channel that drains the field.

The researchers also outfitted each board with antennas to track tagged salmon, confirming that they did swim freely from section to section. Moreover, most of the baby fish chose to stay on the field until it was drained to send them on their way to the sea, suggesting they knew a good thing when they saw it.

Tracking salmon after they left the field showed that many survived the perils of the Delta, which abounds in predatory fish that snap up young chinook as they pass by. “About 30 percent made it out to the ocean,” Buttner says. During drought years, few if any young salmon reach the sea.
Rice grower Steve Neader (left) and Igancio Madrigal of DNH Farms install a board with a hole that lets baby salmon swim freely. Photo by Jim Morris/ California Rice Commission.

NEXT STEPS

The team has drafted step-by-step instructions for rearing salmon on rice fields and these guidelines are now being evaluated by the Natural Resource Conservation Service, which funds the birds in California rice fields program. “We’d like to move to practice standards for a program that growers can sign up for,” Buttner says. Establishing such a program would also require agency approval and, he continues, “we’re in early conversations with the California Department of Fish and Wildlife.”
Releasing tagged young salmon back into a winter-flooded rice field. Photo courtesy of California Rice Commission.

A remaining concern is that during warm winters, the oxygen dissolved in rice field waters could get dangerously low for fish. So this year, the researchers tested a way to monitor field conditions easily. The device measures temperature and dissolved oxygen, and transmits the data in real-time to a website that can be accessed by smartphone. Growers or, as Neader suggests, a third party would then know if they needed to make the call on pulling boards to get fish off the fields.

Next year, the team plans to invite more Sutter Bypass rice growers to participate. Neader, who’s in his second year with the project, thinks the invitation will be well received by his fellow rice growers.

“We’re all rooting for it,” Neader says. “It’s a win-win for everybody.”

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