The Fish Food Story

by Corey Raffel and Jacob Katz, Ph.D.

The saying rang true when Mark Twain coined it, “Whiskey is for drinking. Water is for fighting.”  150 years later it still resonates and throughout the arid West, it is often repeated as gospel.  But in California’s Central Valley an unlikely group of partners are coming together to write a new chapter in the saga of California water. Farmers, water districts, government regulators, and conservation scientists are all putting acrimony aside and getting down to business, working alongside one another to integrate a 21st century scientific understanding of how rivers work and how fish use them into farm and water management. In so doing, they are creating multiple benefits for birds, fish, farms, and people.

The Fish Food on Flooded Farm Fields program aims to help dwindling salmon populations by recreating floodplain-like wetland habitats on winter-flooded farm fields. The program works with rice farmers and water districts to intentionally inundate rice fields in the non-growing season to create the near-ideal conditions to grow the water bugs on which juvenile salmon and other fish depend on as a food source. Tons and tons of water bugs can be grown in these floodplain fields and sent into the nearby river channels where the fish are, to replenish the fish food supplies that have been dramatically reduced over the decades due to the river being disconnected from the natural floodplain.



Fish Food on Floodplain Farm Fields

What started out as a muddy puddle in the corner of a five-acre flooded rice field in 2011 has now grown into a series of landscape-scale experiments utilizing the flood and farm water infrastructure that allows the Central Valley to be among the most intensively farmed and most productive ag landscapes on Earth.  “The Fish Food study expands the Nigiri Concept and shows even where fish can’t leave the river to swim to managed wetlands on floodplain farms, they can still benefit from the nearly 500,000 acres of valley rice fields,” said Katz.

Dubbed the “Fish Food on Floodplain Farm Fields” experiment, this latest study explored the ecological impact and operational feasibility of increasing fish food supplies (i.e., increasing the abundance of zooplankton) in the Sacramento River itself. The experiment relied on existing irrigation and flood protection infrastructure to intentionally flood winter farm fields to encourage the growth of invertebrate food resources for fish. Shallowly flooded fields mimic the natural floodplain wetland conditions where algae and plant matter are consumed by microbes which in turn feed and promote the growth of small insects and crustaceans that are the main source of food for juvenile salmon.

As part of the 2018 experiment, more than 5,000 acres of farmland, owned by California Reclamation District 108 in the Colusa Basin near Knight's Landing, was flooded to a depth of about a foot in mid-November.  The field was left flooded for one month to allow the food web to mature and produce the abundant zooplankton the salmon prefer.  Then, over the next month, one-quarter of the fields were drained per week.  The water, now dense with zooplankton, was delivered through drainage canals to the Rough and Ready Pumping Facility where it was lifted by large pumps into the Sacramento River. 








A Bug Buffet

As expected, the zooplankton counts in the flooded fields increased throughout the study.  And not surprising, was the high percentage of Cladocera, food favored by the salmon, observed in the floodplain water. Over the time of the study, the amount of zooplankton documented in the river at the pumping station outfall increased about 40-fold while the site one mile downstream saw a six-fold increase compared to the upstream site. 

By the end of the study, fish at the pumping entry site were two to three times longer and weighed four to five times more than the upstream fish. Similarly, fish at the downstream sites were two to three times longer and two to three times heavier. These spectacular results indicate that supplementing the river food web with zooplankton-rich water from intentionally inundated farmland during winter when crops are not grown can significantly increase the growth rate of juvenile salmon stuck in the food-scarce river.






A New Era of Cooperation

Critically, this work has been done in an atmosphere of collaboration between all parties involved. Farmers, water districts, government regulators, scientists, and conservationists are working together to move beyond the old Water Wars narrative and, through science, chart a better future for the Central Valley’s fish, farms, and people.  

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