A few dozen baby salmon that spent the past two weeks contentedly eating – and growing – in the invertebrate stew of a flooded rice field were netted Friday, dumped into coolers and hauled by pickup several miles to a drainage canal and to the Sacramento River.
Bobbing in each waterway were three cages where the nearly 3-inch Chinook salmon are going to spend the next few weeks. The reason? To see how well they do in very different bodies of water that happen to all be connected to the same Yolo Bypass flood plain.
It’s the next stage in a years-long research project that seeks to use flooded rice fields as surrogate habitat for young migrating salmon. The researchers plan to do a comparison study to show the difference between fish grown on the flood plain and fish grown in the river.
The Yolo Bypass is an expanse of farmland and natural habitat that stretches from Sacramento to Davis. Once a huge natural flood plain for the Sacramento River that shrank and swelled with the seasons, the bypass was engineered a century ago to divert floods from the city of Sacramento. A substantial portion of the 58,000-acre bypass is farmed for rice the rest of the year.
Scientists have long known that salmon grow faster when they are able to access the Yolo Bypass during floods. There, young fish are protected from predators swimming in the main stem of the river, but, most importantly, they chow down on huge blooms of zooplankton that grow in the floodwaters.
“What makes it such good habitat for fish is that there’s amazing amount of food in these fields, much more food in the fields than there is in the river,” said Jacob Katz, a fishery biologist at the Cal Trout nonprofit and leader of the Nigiri Project experiment at Knaggs Ranch.
Katz and researchers from UC Davis and the Department of Water Resources have spent the past five years introducing tens of thousands of hatchery-raised fish into rice paddies and capturing them as the fields are drained. Katz said the results show the rice-field fish are larger, healthier and more robust than those in the river at the same age.
They are optimistic their results may prompt water and fisheries regulators within the next five to 10 years to modify the levee system to allow Chinook to move back and forth between the river and the rice fields. Some regulators are wary of flood risks.
But Katz says it can be done safely and help Central Valley salmon survive in a future that encourages rice growing in the Yolo Bypass and keeps water flowing to millions of Californians.
“If we can change a little bit of our agricultural management and our water infrastructure,” Katz said, “we can really make a system that works for farming, that works for people, but works much much better for fish in the wild.”