Smithsonian.com
23 March 2015
Jacob Katz stands atop a long, narrow wall of rock and gravel, gazing east over an expanse of off-season rice fields a few miles west of Sacramento. The sky is winter gray and the levee clay is damp and sticky after a brief morning shower.
“When some people look out here, they see a field of mud,” says Katz, a fishery biologist with the conservation group California Trout. “I see the potential for a biological solar panel that can power our entire river system.”
Katz is leading an ecological experiment that places thousands of two-inch Chinook salmon in inundated rice fields for a few weeks, before releasing the fish into the Sacramento River to continue their seaward migration. Katz is interested in how access to floodplains may improve the young salmon’s odds of surviving to adulthood and, eventually, returning to the Sacramento to spawn, a lifecycle that is increasingly hard for salmon to complete due to alterations to the river. Dubbed the Nigiri Project—a reference to the sushi presentation featuring a slab of fish slung over a wedge of rice—the annual experiment has been scaled up over the years, from 10,000 small salmon at its start in 2012 to 50,000 this winter.
Each year, the baby salmon have grown at phenomenally fast rates thanks to an abundance of natural food in the flooded fields. Moreover, their odds of reaching the ocean, it seems, are increased. In the 2013 experiment, 66 of the rice paddy salmon were fitted with surgically implanted acoustic tags. These fish were seven times more likely to be detected by a curtain of hydrophones strung beneath the Golden Gate Bridge than tagged salmon left to navigate the perilous main stem of the river, according to Katz.
Katz and several project collaborators—including University of California, Davis scientists, the California Department of Water Resources and a conservation group called Cal Marsh and Farm—next hope to scale up their experiment to a full-fledged undertaking involving thousands of acres of farmland and perhaps ten million juvenile salmon. The goal is to restore the Sacramento River system’s annual flooding cycle, which native fish species evolved to depend upon.