![]() Young salmon flourish in winter-flooded rice fields because these managed floodplains are spectacularly rich in tiny crustaceans, informally called “bugs,” that make terrific food for little fish. “I was nervous initially - but despite the fact that we’re taking about agricultural fields, it’s pretty good fish habitat.” But he did worry that decomposing rice stubble, which is left on the fields after the fall harvest, would use up oxygen in the water and suffocate the fish. ![]() These agricultural chemicals are applied in the spring and break down fast in the environment. He knew pesticides wouldn’t be a problem in winter-flooded rice fields. That said, it was still a big leap to put young salmon on rice fields. In hindsight, it makes perfect sense because even now the bypass is an expanse of inland sea after heavy rains. “We found that it was a major fish nursery,” he recalls. That perception began to turn around in the late 1990s, when Sommer went into the bypass and saw that many fish species thrive there in wetter winters. Given these extensive alterations, it’s no surprise that biologists assumed the Yolo Bypass was no longer a good place for fish. The land in the bypass is a mix of private farms and duck clubs and public wildlife areas.īirds enjoy the food-rich shallows of Delta floodplains and rice fields as much as fish. Sacramento River floodwaters pour into the bypass at the top and flow out to the Delta at the bottom. Built about 100 years ago, the bypass is an imposing structure: 40 miles long, two to three miles wide, and bounded by 20-foot earthen levees. Today much of this historical floodplain is occupied by the 59,000-acre Yolo Bypass. Salmon were so plentiful that people with handheld nets hauled in tremendous catches from the banks of the Tule Canal, an early effort to drain the basin that was built in 1864. Young salmon grew big and fat in the basin’s floodplain nurseries on their way down to the ocean, and returning adults swam back up the basin toward their natal spawning grounds. The Yolo Basin was also a paradise for salmon and other fish. Hastings recounted the spectacle in his 1945 book The Emigrants’ Guide to Oregon and California, describing the innumerable flocks as “at times blackening the very heavens,” and their “tumultuous croaking and vehement ” as almost deafening. Astonishing numbers of geese and ducks thronged to the basin to feed and rest during their winter migrations along the Pacific Flyway. Herds of tule elk wandered the basin’s marshes and grizzly bears abounded. Atwell told of “simply immense rushes, which cover the ground with an almost impenetrable thicket.” In an 1870 volume called The Western Shore Gazetteer, Yolo County, C.P. The rest of the Yolo Basin was dominated by freshwater marsh filled with dense stands of tule more than 10 feet high. Riparian forests thick with cottonwoods, sycamores, and oaks grew on natural streamside berms. These floodwaters moved slowly in a broad sheet through the wetlands to the Delta, taking so long to drain that the basin was impassable half the year. As rainstorms swelled the river and local streams, floodwaters overtopped their banks and spread over the basin at depths ranging from as much as 20 feet by the riverbanks to just a few inches farther out. Early accounts described the basin as an immense sea during severe winters. The Yolo Basin was once an enormous wetland along the Sacramento River, covering an area about 40 miles long and up to seven miles wide from what is now Knights Landing to the Sacramento-San Joaquin Delta. ![]() “We’re looking for creative solutions - can we make farming more fish friendly?” The big question is whether fields that produce rice can also be managed as floodplains. ![]() “They’re one of the more important areas we could improve,” Sommer says. Today, however, most of the low-lying land along California rivers is leveed and farmed. “There’s been a long-term decline in Chinook salmon.”įloodplains once served as nurseries for young salmon migrating from mountain streams to the ocean. “There’s some urgency,” says lead author Ted Sommer, a native fish expert at the state Department of Water Resources, which manages the Yolo Bypass as a floodway. Now, after nearly a decade of testing fish in fields, a new paper in San Francisco Estuary and Watershed Science outlines lessons learned as well as next steps in managing floodplains for salmon. Salmon in this managed floodplain grew so fast - averaging more than one millimeter per day - that they outpaced young Chinook elsewhere in the region. The team found that rearing fish on farms works better than they had ever dreamed. In 2012 a team of salmon researchers tried a wild idea: putting pinky-sized Chinook on a rice field in the Yolo Bypass, a vast engineered floodplain designed to protect the city of Sacramento from inundation.
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