Eric Holmes of the UC Davis Center for Watershed Sciences throws a net to sample the density and types of invertebrates that live in Sacramento Valley waters. His team's research found that floodplains, like those in the Butte Sink, teem with food for ducks and salmon as compared to rivers and other wetlands.

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BY DR. JACOB KATZ
(Originally published in the Summer 2020 issue of California Waterfowl)

A biologist pulls his net from the muddy waters of the Sanborn Slough duck club. Dozens of plump young salmon wriggle in his hand. “This place is amazing,” says Eric Holmes of the UC Davis Center for Watershed Sciences. “The Butte Sink is one of the few places left in the Valley where salmon can predictably get onto the floodplain and find something to eat.”

That’s right: Fat, happy salmon in a duck marsh.

Holmes is one of a team of researchers from UC Davis and California Trout who are investigating how floodplains like the Butte Sink are good for both thriving waterfowl and struggling salmon. They’re researching at the invitation of California Waterfowl, which owns and maintains Sanborn Slough. So far, results are very promising and could show that wetlands that are good for ducks and duck hunters are also good for endangered salmon, and that wetlands may be a big piece of the puzzle to help restore Chinook salmon populations in the Central Valley.

RIVERS DIVORCED FROM PLAINS

The Butte Sink represents the largest remnant of Sacramento Valley floodplain that still functions under much the same pattern as it did historically. That’s because the Sink is the only place in the Valley that is still flooded every wet season directly by surface waters from fish-bearing streams.

The Yolo and Sutter bypasses are the other large-scale floodplains still inundated by river water. But they only spill over engineered low spots in the river levees during the larger flood events that tend to occur every couple of years. In contrast, Butte Creek and its tributaries — which meander through an extensive network of farmland and managed and permanent marshes — consistently spill into the adjacent fields and wetlands of the Butte Sink, covering tens of thousands of acres multiple times every wet season. Riparian forest surrounds the creeks and sloughs, creating a mosaic of natural habitat, managed wetland habitats and farmed fields. This actively managed yet diverse patchwork of working lands is host to one of the greatest concentrations of wintering waterfowl on Earth, with as many as 2 million waterfowl visiting every year.

The watershed also hosts the only relatively stable population of endangered spring-run Chinook salmon in the Sacramento Valley. Butte Sink and Sutter Bypass play an important role in Butte Creek’s salmon success because they provide consistent access to floodplains that are rich habitat for juvenile fish. The fact that young salmon can, on their downstream journey to the Pacific Ocean, access the flooded fields and marshes of the Butte Sink is what sets Butte Creek apart from all other Sac Valley tributaries. The floodplain habitats of Butte Sink are essentially a massive bug buffet for young salmon.

Direct connections between rivers and wetlands allow these lucky fish to take advantage of the tremendous food resources created in the fertile floodplain habitats. This is a feast that other salmon populations aren’t able to enjoy because levees are cutting off most stream channels from the wetlands. The forage-rich floodplains make Butte Creek salmon stronger, larger and better equipped to survive the perilous journey that will take them to the ocean for several years before they return as large adults to the streams where they were born.

The Center for Watershed Sciences and CalTrout are monitoring fish and food at Sanborn, CWA’s 260-acre acquisition in the heart of the Butte Sink. It’s the perfect place for Holmes and the team to get a better understanding of how floodplain wetlands can be managed to provide critical habitat for both waterfowl and salmon. We all want salmon to recover, and we all want waterfowl to thrive. This research could show that encouraging government agencies and private landowners to create more habitat for waterfowl and hunters through voluntary, incentive-based programs, is also a perfect prescription to recover endangered fish. But can both populations — ducks and salmon — coexist?

FOOD IN THE FLOODPLAIN

It’s easy to see why waterbird populations have flourished over the last several decades with the proliferation of winter farm fields being intentionally flooded as surrogate wetland habitat for waterfowl. They are called puddle ducks, after all. And after more than a century of management that kept winter floodplain fields relatively dry, we are again seeing widespread “puddles” on the landscape. Most critically, the creation of this seasonal bird habitat occurred at a landscape scale that could impact entire populations. With hundreds of thousands of acres of winter farmland flooded annually, the past decade has seen some of the highest counts ever recorded for waterfowl and shorebirds in the Valley.

Meanwhile, Chinook salmon populations that are confined to food-starved river channels, cut off from floodplains by levees, have hit historic lows. Fish may not be able to fly but they still need to eat. Yet levees — so easily flown over by birds — exclude salmon from their floodplain food supply.

Fortunately, much research has shown that when salmon are given access to inundated floodplain habitats, they grow much faster than when they are confined to adjacent river channels by levees. And it’s not hard to see why. There is so much more food on the floodplain. Like birds, salmon react quickly and favorably when allowed access to productive floodplain habitats similar to those they evolved with and are adapted to.

The recovery of salmon and other native fish populations will likely be impossible without allowing them access to the long-duration inundation flood patterns that are the foundation of the Central Valley’s aquatic food web and that have so benefitted birds. The opportunities are many and varied, but the operational improvements we are developing together on working floodplain farms have the potential to create multiple benefits for agriculture, flood protection, and fins and feathers — all while improving water security for 25 million Californians.

The work at Sanborn and elsewhere in the Central Valley is of high interest to duck hunters and landowners, said Mark Hennelly of California Waterfowl. “Any push to adopt new water-use practices should be done in cooperation with landowners so it is voluntary and incentive-based as opposed to regulatory,” said Hennelly, who is CWA’s vice president of legislative affairs and public policy.

DUCKS AND RICE

Growing up in the Valley in the 1980s, we were all used to the smoke. The haze from the burning rice fields hung in the autumn air, stung the eyes, obscured the Sierra, brought the horizon close. But then in the early 1990s, clean-air legislation caused the rice industry to pivot away from burning. Growers instead began to flood their rice fields after harvest. Flooding accomplished the same objective that burning had: It broke down the rice stubble left in the field after harvest, easing soil preparation for spring planting. And it had the obvious advantage of doing it without the smoke.

But then something marvelous and unexpected happened. The ducks and geese – accustomed to bypassing the valley because its wetlands had been drained and little habitat remained – looked down and saw the wetlands of the Pacific Flyway, their ancestral winter home, glistening again. Suddenly, almost miraculously, fields that had been diked and drained a century earlier to develop the fertile floodplains of the Sacramento Valley for agriculture, had become seasonal wetlands again. Growers saw how their flooded winter fields attracted the birds. Conservationists and wildlife agencies noticed as well. The rice industry rapidly embraced a good idea, and rice became California’s most wildlife-friendly crop. As the practice of winter flooding grew to tens of thousands, then hundreds of thousands of acres, waterfowl populations experienced a spectacular resurgence. This was the birth of a conservation success story that would become an environmental model of national significance.

The Pacific Flyway is now recognized as migratory bird habitat of hemispheric importance. The Sacramento Valley now boasts some of the highest densities of wintering waterfowl anywhere on the planet. And farm life was not upended with this metamorphosis. Great swaths of ag land have not been abandoned. The farm economy does not lie in shambles. This was not some grand compromise between people and the wild. This revolutionary outcome came, not from radical change, but from an adjustment to farm operations in rice country. Winter bird habitat was created on flooded farmland that remained in active summer production. This wasn’t a trade-off. It was a huge win-win.

Over the intervening three decades, the practices and incentive programs that support flooding winter farm fields have been expanded to create habitat not just for ducks and geese but also for migrating shorebirds – stick-legged sandpiper-like birds with fantastic names like whimbrel, killdeer, rednecked phalarope, and snowy plover – all making the arduous journey from the Amazon to the Arctic. Small birds, too, on this perilously long, hemisphere-spanning annual round trip can now rely on shallowly flooded rice fields to rest and refuel. Birds of different sizes require water of different depths. So programs meant to provide waterfowl habitat look for water depths of approximately 6 and 12 inches, while shorebird programs prescribe depths of several inches max.

Multiple-benefit, on-farm solutions will be an important component of updating California’s outdated water systems so that our limited water resources can meet the needs of the sixth-largest economy on earth, while preserving our state’s spectacular natural heritage. The past several decades have demonstrated how on-farm solutions can sustain the habitat and food resources necessary to support a diversity of water-bird populations. Now we have the opportunity to expand the tool-set to include salmon as well. This work is showing that imperiled species and regulation need not be an inevitable consequence of development.

Historically, California has managed rivers as separate from the landscapes through which they flow. But by recognizing that the flow of water across floodplains is a critical aspect of water management, we can re-integrate fish, wildlife and natural processes into the design and operation of the water system. Building on what we learn at places like Sanborn Slough, we can develop science-based programs that incentivize public agencies, landowners and water districts to collaborate on multi-benefit solutions that work for the farms, the fish and the fowl of the Pacific Flyway.

Click here to see more about the research and results.

STUDY HIGHLIGHTS

WHAT THEY'RE DOING AT SANBORN: Researchers are taking water samples to measure the level of nutrients available for fish, and rearing salmon smolts in submerged pens there to measure their growth relative to smolts in other water bodies.

WHAT THEY'VE FOUND: They knew floodplains have more nutrients than rivers, but it turns out the Butte Sink - famous for its abundant waterfowl and well-managed water systems - has the highest level of nutrients of all the water bodies they've studied, even more than the Yolo Bypass or Sutter Bypass. The endangered Chinook salmon they've raised in floodplains have the highest growth rates.

WHAT THIS MEANS FOR DUCKS AND DUCK HUNTERS: The research is showing it’s possible that maintaining high quality duck habitat and restoring beleaguered salmon populations can happen at the same time – without one goal coming at the expense of the other. This has not been the case in the Klamath Basin, where water has been kept from the Lower Klamath NWR and sent down a river for salmon, turning the refuge into a desert at times, which is especially bad for ducks breeding and molting at the refuge. Click here for more information about California Waterfowl's efforts to save Lower Klamath. Similarly, plans to flood the Yolo Bypass intentionally more often for the benefit of fish will also come at the expense of duck clubs and public hunting lands in the Bypass. While those policies are tough on ducks and duck hunters, the research at Sanborn shows that birds and fish both benefit from shallow, natural water movement over floodplains as opposed to channels and rivers.

More floodplains, more salmon and ducks? That’s what the research is showing.

“By building levees, we’ve created rivers that are essentially food deserts,” said Dr. Jacob Katz of CalTrout. Working with Dr. Carson Jeffres at UC Davis, they’ve found that zooplankton density was often 10 to 100 times higher, and sometimes even higher, in the wetlands than in river channels.

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