Innovative projects in California are using flooded rice fields to rear threatened species of Pacific salmon, mimicking the rich floodplains where juvenile salmon once thrived. This technique also shows promise for growing forage fish, which are increasingly threatened in the wild.
The idea of rearing salmon in fallowed rice fields started in a duck blind. Huey Johnson, California’s Secretary of Resources in the 1970s and at age 82 widely considered the grand old man of California environmentalists, is an avid hunter, who has spent hundreds of hours in Central Valley duck blinds. It is perhaps a testament to the contemplation induced by extended time spent in blinds that Johnson, surrounded by winter rice fields flooded to decompose rice straw, began wondering what else could be done with all that water. His answer: Grow fish. With two environmentally minded investors, Johnson formed a company called Cal Marsh & Farm Ventures that in 2011 acquired a Northern California rice field to carry out fish experiments.
As it happened, in the late 1990s two scientific teams one led by Ted Sommer, a floodplain biologist in California’s Department of Water Resources, and the other by Peter Moyle, a University of California, Davis, biologist and leading inland fish expert had begun carrying out similar experiments in the Central Valley. They sent juvenile salmon downstream across floodplains instead of via rivers, where predators were more numerous. Their work showed that juvenile salmon diverted from the Sacramento River’s main channel and retained in its adjacent floodplain for a few weeks grew more than twice as fast as fish that stayed in the river.
In 2012 Cal Marsh & Farm Ventures and the scientists joined forces in the Nigiri Project, named after a kind of sushi because both combine rice and fish, to use rice fields to promote salmon restoration. The scientists have since compiled persuasive evidence that salmon benefit greatly by lingering in flooded rice fields, while Johnson has started another enterprise that uses rice fields to grow forage fish for protein.
The salmon project is likely within a year or two of overcoming the last bureaucratic obstacles keeping it from operating as a government-sanctioned method of mitigating environmental harm. Though less-developed, the forage fish venture offers the prospect of global impact by taking pressure off of wild fish stocks. Both projects suggest the rising influence of “reconciliation ecology,” which argues for the reconfiguration of human-dominated landscapes to include other species as the only way left to sustain most ecosystems.
Two centuries ago the Central Valley was largely a marshy wetland. When the Sacramento River flooded, juvenile salmon beginning their journey downstream to the ocean were cast onto its floodplain, where they stayed for months, fattening themselves on plankton and insects that were part of the floodplain’s biological cornucopia. But the construction of ever-higher levees in the 19th century, vividly described in Robert Kelley’s 1989 classic Sacramento River history, Battling the Inland Sea, separated the Sacramento from its floodplain.
The result was that salmon were hurtled down the river’s main channel, reaching the Sacramento-San Joaquin River delta and the Pacific Ocean too early, when they were underweight and unprepared for predators. Combined with dams, gold mining, and water diversions for agriculture and municipal consumption, the river’s isolation from the floodplain has reduced three of the Sacramento’s four salmon runs to endangered levels.
Southeast Asians have raised fish in rice fields for many centuries, but they do it while the rice is growing, using fish suited to the paddy water’s warm temperatures. What distinguished Johnson’s idea from the traditional Asian practice was that he wanted to grow salmon in the winter, after rice was harvested and water temperatures were low enough for salmon. This wasn’t even possible until the early 1990s, when California’s clean air laws placed tight restrictions on burning rice straw, the farmers’ preferred method of eliminating rice residue.
Farmers then began flooding their fields starting in the late summer or fall, inadvertently producing a simulacrum of the vast 4-million-acre Central Valley wetlands that had existed two centuries ago. Winter-flooded Central Valley rice fields now cover a larger area 250,000 to 300,000 acres than the 200,000 acres of original valley wetlands that remain.
The switch to flooding has generated a huge resurgence of the Pacific Flyway, as millions of migratory birds desperate for water in the increasingly drought-prone valley began using the rice fields as way stations. Politically vulnerable because of their high use of water in an increasingly water-scarce state, rice farmers found themselves cast as environmental heroes, and embraced the herons, egrets, ducks, geese, sandpipers, and other birds that thronged to their fields. Rearing fish could add to the rice farmers’ environmental credentials while supplementing their incomes with mitigation fees paid by the state’s water users.
The production of rice and fish on the same field is a prime example of reconciliation ecology, first articulated in a 2003 book called Win-Win Ecology: How the Earth’s Species Can Survive in the Midst of Human Enterprise. The author, Michael L. Rosenzweig, a University of Arizona ecologist, argues that humans have so thoroughly transformed the earth’s surface that environmental restoration is impossible on virtually all of it, and the few areas set aside as natural reserves aren’t big enough to sustain many species. Instead, he says, the only way to ward off mass extinctions is to convert working landscapes to support other species while continuing to fulfill human needs.
Reconciliation ecology represents a shift among environmentalists from focusing on a particular place, such as a nature reserve, to a natural process. We invest a lot of money in postage-stamp, high-profile conservation efforts that really are just a blip on the larger landscape, Jacob Katz, the Nigiri Project’s lead scientist, said. Instead, we should be thinking about how water flows across the entire landscape and managing those natural processes so that basically the habitat takes care of itself.
The juvenile salmon reared in the Nigiri Project may benefit rice fields as much as rice fields benefit them, while both foster the resurgence of the floodplain food web. Floodplains are much richer, more varied biological environments than rivers; reconnecting floodplains to rivers infuses downstream basins with life. Flooded rice fields awaken dormant plankton in the soil, insects flourish on the plankton, and the fish dine on both. In turn, the fishes’ presence reduces insects, weeds, and diseases that may harm rice.
Rice farming is often criticized for its sizable water use, but it’s the only crop that flourishes in the Sacramento Valley’s clayey soils. The clay holds back the water from percolating deeper into the soil and contains it in the fields until they’re drained in March.
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