Rice Fields for Fry

Tom Walker
January 29, 2016
By Tom Walker

Any sushi lover will tell you that salmon and rice are an ideal combination.….

Aptly named the Nigiri project, after the fish and rice sushi combo, the experiment has run the last four years in cooperation between the California Departments of Fish and Wildlife and Water Resources, University of California Davis, California Trout, US Bureau of Reclamation and NOAA.  The program is based at the Knaggs Ranch in California’s Yolo County, on the Sacramento River flood plain.

Jacob Katz who works with California Trout and is the manager of the Nigiri project says that his graduate studies showed him that more than three quarters of the fish species in California, including the four Chinook runs are in serious decline.  “…Headed towards extinction if something wasn’t done,” says Katz by phone. 

The solution, says Katz, “are fundamental changes in the way water flows across the California landscape.”   He adds that we place a lot of emphasis on salmon habitat and spawning and less on how the small fish behave and survive.

Channels and dykes

Over the past 200 years the Sacramento River has been systematically channeled and dyked to control flooding, and wetlands have been drained to provide arable land for farming.  But that process has destroyed some two million acres of wetlands that used to provide habitat for waterfowl and a nursery for salmon.  The remaining 5% simply cannot do the job.  

Reclaiming the land to its original state is not an option and water and land managers look for ways to further utilize the existing agriculture footprint.

Major crop

Rice is a major crop on the Sacramento flood plains. Since the early 1990s rice farmers have been flooding their fields in winter, as an alternate means of decomposing straw that clean air legislation prevents them from burning.    That’s been a bonus for waterfowl that now use the “reconstituted” wetlands.  Four years ago these man made-wetlands took on a second traditional role.  They became a nursery for Chinook salmon juveniles.

Fish are raised in rice fields across Asia, usually when the rice is growing through the summer months.  California’s Central Valley is too hot for salmon in the summer, but winter-flooded fields seem to work quite well.

Fall run Chinook from the Feather River hatchery as well as naturally spawned fish, are used in the program.

The Nigiri project plants out 45 mm long juveniles.   “That’s the minimum size where tags can be implanted and the fish are several weeks old at that point,” says Katz.  The fish are moved into flooded rice fields in February and in 3-6 weeks they swim out to the river as the fields are drained and the farmers continue with their spring rice plantings.  Katz says that the same water infrastructure that is used to irrigate the fields in the summer is used for flooding and draining.

Rich habitat

The salmon benefit from a rich habitat that forms when water covers the fields.  Carson Jeffres, field and laboratory director for the Center of Watershed Sciences at UC Davis calls it a “dehydrated food web” - just add water.  It creates, as Katz says, “An incredible engine of productivity”

Fish in the river channels (an environment that essentially starves fish) also benefit.   When the flood plains are drained, they carry out nutrients for food on the other side of the levee.  

Phenomenal growth

Katz describes the fish growth as “phenomenal”.  They gain  1mm in fork length a day and double their weight on a weekly basis.   That’s 2 to 5 times faster than in a hatchery; they’re nicknamed “flood plain fatties”.  “They basically swim around with their eyes closed and their mouths open,” he quips.

50,000 fish went into the rice fields in 2015 and the target is 150,000 this year and 1 million for 2017. 

“We would like to see paired releases of a quarter million fish at four different Central Valley floodplains in each of the next four years,” says Katz.  250,000 fish would be released onto the flooded fields and another quarter million into the adjacent river channel. They could then track differential recruitment to ocean fishery and escapement from floodplain-reared and river smolts.

While the project has been underway for four years, Katz says that the small volume of fish they are working with makes it difficult to asses returns.  “We are advocating changes within state and federal practices to get more fish out onto the flood plains so we can more accurately track their migration.”

Cost savings

“The direct potential savings in hatchery costs could be substantial from stocking fry in great numbers directly onto managed floodplains,” says Katz.   “But we have never done a financial analysis.”

Flood plain smolts are expected to be stronger, larger and more practiced at evading predators than their hatchery and river channel-raised cousins, qualities that should increase their chances of survival and return, which may aide the Sacamento River’s threatened Chinook salmon population.

“There are no downsides here,” concludes Katz.   “It is not a compromise.  Water is not being taken from anyone else; land isn’t being taken out of production.  What we are doing is increasing the productivity of the valley as a whole.”

Tom Walker

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