Study adds evidence that rice fields can aid salmon rearing

juvenile salmon
Juvenile salmon, photo courtesy Carson Jeffres/UC Davis

Idle rice fields in the winter can act as surrogate floodplains to help rear juvenile salmon, according to a recently published study.

Titled “Floodplain Farm Fields Provide Novel Rearing Habitat for Chinook Salmon,” the study provides further evidence that idle Central Valley farm fields can have environmental benefits for California’s salmon populations.

It was published in the the journal PLOS-ONE and is based on work by scientists from the nonprofit group, California Trout; University of California, Davis; and the California Department of Water Resources.

“This study demonstrates that the farm fields that now occupy the floodplain can not only grow food for people during summer, but can also produce food resources and habitat for native fish like salmon in winter,” says lead author Jacob Katz of California Trout. “Our work suggests that California does not always need to choose between its farms or its fish. Both can prosper if these new practices are put into effect, mimicking natural patterns on managed lands.”

About 10,000 small, hatchery-reared salmon, averaging less than 2 inches and weighing about a gram, were transplanted to a 5-acre field for several weeks between the fall rice harvest and spring planting.

A subsample of the fish carried unique electronic tags similar to chips used to identify pets to allow tracking of individual growth rates. Growth turned out to be some of the recorded in freshwater in California.

“By reconnecting rivers to floodplain-like habitat in strategic places around the Central Valley, we have the potential to help recover endangered salmon and other imperiled fish populations to self-sustaining levels,” Ted Sommer, lead scientist for the CDWR and a co-author, said in a news release.

Since 2012, the scientific team has been examining how juvenile salmon use off-channel habitats, including previously harvested rice fields. The experiments provide evidence that rice fields managed as floodplains during winter can create “surrogate” wetland habitat for native fish.

The work suggests that shallowly flooded fields function in similar ways to natural floods that once spread across the floodplain. The natural floods supplied extremely dense concentrations of zooplankton—an important food for juvenile salmon.

Foraging on these nutritious invertebrates, the young salmon grow quickly, improving their chances of surviving migration to sea and returning in three to five years as the large, adult fish.

Since this original study, the team has continued to investigate how rice fields and other managed habitats could be improved to support salmon rearing.

“This study shows that we can start focusing on solutions that support fish and people, instead of one or the other,” said Carson Jeffres of the UC Davis Center for Watershed Sciences, the second author on the report. “It’s a huge win-win.”

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