The rice fields of California’s Sacramento Valley are remarkably versatile. They produce virtually all of America’s sushi rice – and then the flooded rice fields feed millions of migrating birds in the fall and winter. Now those same rice fields could help restore dwindling salmon populations by making sure the fish are well fed before they head out to the Pacific Ocean.

In the early 1990s, California rice growers changed how they farm in order to protect millions of migrating birds, by leaving their fields shallow-flooded for specific periods of time after their crop was harvested. This practice mimicked the wetlands that existed before deep, fast-flowing canals were created, providing a place for birds to rest and feed on their long migration north. 

Now the California Rice Commission, along with University of California Davis and California Trout, is exploring how best to raise juvenile salmon in the flooded rice fields. It is in the second year of a $1.4-million pilot research project, Helping Salmon in the Sacramento Valley, that will develop guidance for farmers about how to prepare their fields so the salmon grow fat before they are released into the ocean.

While it may seem a long way from growing rice to tracking salmon from Knights Landing all the way to the Golden Gate Bridge, there is a logical connection – the rice fields have become the surrogates for California’s historic wetlands, which have almost all disappeared, and where fish once grew before migrating to the ocean. 

All the evidence suggests that these surrogate wetlands are “incredible habitats for fish”, says Andrew Rypel, Associate Professor and Peter Moyle Chair of Cold Water Fish Ecology at UC Davis. Water flows on to the fields in summer through irrigation systems, then flows out – full of fish food – through the same system in winter.

“The need for restoration for the salmon population in California has been apparent for years,” says Paul Buttner, manager of environmental affairs for the California Rice Commission. “Since they are anadromous, they have to have the right conditions to move from the river into the flood plain where a rich food web enables them to grow quickly for their journeys out to the ocean. Many organizations are working on this initiative, but we are specifically working on reconnecting the flood plain and creating quality habitats for these salmon to thrive in rice fields located in the valley.” (Anadromous is the term that describes fish born in freshwater who spend most of their lives in saltwater and return to freshwater to spawn.)

Part of reconnecting the flood plain involves extending the duration of natural flooding in the Sutter and Yolo Bypass, so fish have a longer time to grow in those fields, and that is what the pilot project is working toward. The other part will be to integrate the rice fields outside the bypass by flooding them, growing fish food there, and draining that water back to the river when juvenile salmon are migrating down the river and need that extra food, says Jacob Montgomery, project manager for California Trout’s Central Valley region.

In a living scientific experiment to see if any extra treatments, such as deep channels or vegetative cover, make the rice fields even better habitat for young salmon, researchers created four kinds of experimental plots within the Yolo Bypass area to see which ones were the most ‘fish-friendly’. They included fields with deep trenches designed to provide cooler temperatures and allow fish to hide from bird predators; fields filled with woody debris from discarded Christmas trees; fields with trenches with woody debris; and flooded fields with no treatment. Each plot had a drainage structure to maximize fish passage and collection.

During the winter of 2019-20, about 1,125 baby salmon were placed in each of the eight, half-acre test plots at River Garden Farms in Yolo County, flooded to about 12 to 18 inches deep. About 1,000 of the fish swam freely but were periodically captured, measured, marked and released. About 125 were in protective cages so they could be fitted with tags that would let the researchers track each fish individually.

Lead scientific researcher Rachelle Tallman said most of the plots recorded fish survival rates between 70% and 78%, and that was encouraging. They were worried that the woody-debris method might show the highest survival rate and that would mean asking farmers  “to put a ton of trees out in their field,” she says. 

“So I think it actually makes it easier in the sense that you can just process your rice and leave it, add water and hypothetically add fish, and it would show a similar survival to someone who maybe did more.”

After their time in the test plots, the salmon were released into the Sacramento River, including about 1,000 fish equipped with tags that were tracked on their journey into the Pacific Ocean. A special ‘paired release’ study compared the rice-fed salmon with fish that had been raised in hatchery-like conditions at UC Davis.

Tracking data showed that 4.5% of the salmon from the rice fields made it, compared to just 1% of the control salmon. As salmon survival rates vary from year-to-year, with survival in drought years being typically around zero to 3% up to as high as 15 to 20% survival in rare high-water years, these results were promising indeed.

“We could not be happier with these results, and they will now serve as the basis for further work by CRC and our fish conservation partners to continue efforts to develop a larger-scale strategy to use our fields to help salmon, just as we have used them to help birds for decades now,” says Buttner.

The next steps will be to see if the pilot can be scaled into full-sized, working rice fields with more salmon and hopefully including state and federal agencies’ involvement to help monitor implementation. “It is anticipated that three to five years from now, we could have a fully implemented program. The Rice Commission would promote it heavily and would work closely with growers to integrate them into the program,” Buttner says.

“We want to answer all the questions that we need to answer about what exactly is it that we need the growers to do,” he says. “Is it a physical modification of the field? Is it an alteration of how they flood the field, how they drain the field, the timing of drainage? These are all the questions that we need to answer in order to work with Natural Resources Conservation Service (NRCS) to develop that conservation management practice.”

Ultimately, the Commission wants to create standardized management practices for farmers. “What we want to do is get to a point where a grower could enroll in this practice and participate in wintertime fish conservation activities,” Rypel says. “So rather than just letting the field go fallow and not use it at all during the winter, let’s use it for something. Let’s use it for fish conservation.”

The innovative project is supported by a diverse group of sponsors, led by the USDA’s Natural Resources Conservation Service, Syngenta Crop Protection LLC, and State Water Contractors, showing the widespread interest in this work.

The California rice industry has a long history of implementing various conservation practices, and using the rice fields to grow salmon can help carry on that tradition.  “The Sacramento Valley is a very special place,” Buttner said. “We want to make sure that that legacy is continued.”  

Sources:

Helping Salmon in the Sacramento Valley. California Rice

Research tests how rice fields can benefit fish. AgAlert, Mar. 25, 2020

California Rice Salmon Pilot Project Making Steady Progress. Agnet West, Apr. 13, 2020

Positive Results Shows Promise for CA Rice Commission Salmon Project. Grow West, Winter 2021.

Followup:

California conservationists and farmers unite to protect salmon. Reuters, Feb. 9, 2022

California’s Floodplains Are Coming Back, and So Are Their Salmon. Reasons to be Cheerful, Apr. 1, 2022