ROBBINS, Calif., Feb 9 (Reuters) - In an experiment a decade in the making, biologists are releasing hatchery salmon onto flooded Northern California rice fields, seeking to replenish endangered fish species while simultaneously benefiting the farmers' business model.

At a time when environmentalists are often pitted against agribusiness in California's water wars, conservation scientists and rice farmers are working together, trying to reclaim the great flood plains of the Sacramento River for salmon habitat.

Their task is daunting. California's wetlands have all but disappeared, converted into farms and cities in one of the great engineering feats, or environmental crimes, of the 20th century.

Now, for the cost and inconvenience of flooding their fields, rice farmers are earning goodwill and betting that a healthy salmon population will avoid new regulations to protect wildlife and keep adequate water flowing.

In recent years, biologists discovered that as rice straw decomposes in flooded fields it creates a broth rich in fish food. They call it "zoop soup."

"The zooplankton are so big and they're so juicy, it's like filet mignon," said Andrew Rypel, a professor of fish ecology at the University of California Davis and lead investigator on the project.

After fattening up on their zooplankton, the salmon return to the river, swim downstream and beneath the Golden Gate Bridge on their way to sea, returning years later to spawn the next generation.

The university's researchers have joined the California Rice Commission, the conservation group California Trout and the U.S. Department of Agriculture on the project, seeking to reverse the trend toward dwindling fish populations as a result of human re-engineering of the state's waterways and, in recent years, extreme drought exacerbated by climate change.

"We don't want to just sit silently while extinctions happen," Rypel said.

Before industrialization, the northern end of California's Central Valley was a miles-wide flood plain straddling the Sacramento River - a natural feeding ground for fish.

After one too many floods in the city of Sacramento, and realizing that Mississippi River-style levees were insufficient to contain the diluvial bounty, California built two bypasses in the Sacramento River for flood control and irrigation.

That land is ideal for farming rice, and about 500,000 acres (200,000 hectares) are under cultivation today.

Though the natural state will never be restored, the flood plain can reconnect to the river. Enhancing salmon habitat in the flood plains helps the fish grow big early in life, improving their chances of survival.

So far the results show juveniles feeding in the rice fields grow two to five times faster than those in the river channel, said Carson Jeffres, another researcher with the UC Davis Center for Watershed Sciences.

Though the experiment has placed salmon on small parcels before, this winter marks the first time it has been tried on a large scale on a working rice farm. Conservation scientists hope to replicate the model on more farms in years to come.

The salmon project is using 389 acres (157 hectares) on a pair of rice farms at the Sutter Bypass near Robbins, about 30 miles (50 km) northwest of Sacramento. One farm is intentionally flooded with water and planted with hatchery fish, enabling the biologists to study their progress and tag some with microchips to track their movements.

A second farm is being prepared just in case the Sacramento overflows this year, delivering naturally spawned salmon.

Continue reading the article from Reuters here.