By Robin Meadows
It’s a lovely December morning in Rio Vista, a town of 10,000 in the Sacramento-San Joaquin Delta. The sky is a soft blue, the sun brings welcome warmth against the chill, and the water is calm with just a hint of ripples―ideal conditions for the team of state and federal biologists standing on a boat launch on the Sacramento River at 8:30 am. They’re here to release captive-raised Delta smelt, a small endangered fish unique to the region, into the wild.
The clock on the release began ticking at 7 am.
That’s when another crew started loading the smelt into insulated cylindrical drums called carboys at the Fish Conservation and Culture Laboratory, a conservation hatchery about 30 miles south near the town of Byron. The hatchery, operated by the University of California, Davis, has maintained a genetically-diverse captive population of these imperiled fish since 2007.
The water in the carboys starts out rich in oxygen but the smelt begin using it up the second the lids snap shut. The team waiting on the boat launch has four or five hours to get the fish safely into the water at the Sacramento River release site.
The 7 am start means finishing by noon at the latest.
Shortly before 9 am, a truck hauling 3,200 Delta smelt in 16 carboys pulls up to the boat launch. The team springs into action. Handling the carboys, hefty at 180 pounds each, requires a light touch. “Delta smelt are notorious for sensitivity to their environment,” says Fish Conservation and Culture Laboratory director Tien-Chieh Hung. “Temperature, chemicals, physical disturbance―splashing pins them to the wall.”
“Everything about this fish is a challenge,” Hung continues.
But this is the third year of these releases and the team has it down. In less than half an hour the carboys are secured on two boats that immediately zoom downriver toward the release site.
It’s now 9:20 am.
Delta smelt once abounded. “We used to catch thousands in surveys, then hundreds, then tens, and then hardly any or none,” says Steven Slater, a California Department of Fish and Wildlife (CDFW) environmental scientist on the release team. The many threats to Delta smelt include loss of their wetland habitats; a steep drop off in their food, tiny aquatic creatures called zooplankton; and rampant introduction of non-native species, which now outnumber natives in the Delta.
One threat stands out in particular because it puts Delta smelt at odds with people: loss of the freshwater flows that keep the Delta from getting too salty for these fish. Much of California’s water supply drains through the Delta, the natural westward flows keep the briny ocean water at bay.
But people have engineered the region to benefit themselves. State and federal water projects pump vast volumes south, delivering drinking water to 25 million people and irrigating nearly 4.5 million acres of San Joaquin Valley farmland.
Protections for Delta smelt can curtail water exports, creating tension between water users and fish advocates. Peter Moyle, a UC Davis biologist who sounded the alarm over the smelt’s decline across his decades of studying them, called them a “beautiful little fish, very delicate and translucent.”
Former Congressman Devin Nunes, who represented the thirsty San Joaquin Valley farms that rely on water from the Delta, called them a “stupid little fish.” And Fresno-area congressional candidate Chris Mathys wanted them declared extinct.
To those who say it’s too late to save Delta smelt and question even trying, U.S. Fish and Wildlife Service biologist Katherine Sun shoots back her own question.
“Why wouldn’t you try?” asks Sun, who studied with Moyle a decade ago and now coordinates the Delta smelt release team, a multi-agency effort that also includes the California Department of Fish and Wildlife, the California Department of Water Resources, UC Davis, the U.S. Bureau of Reclamation, and the U.S. Geological Survey. “UC Davis has been working for years to retain their genetic diversity―why wouldn’t you capitalize on that?”
Sun stands in one of the carboy-laden boats speeding toward the release site near Decker Island, once a favorite wintering spot for the fish. Winter is Delta smelt breeding season, and releases typically start in November and end in January. “We target the sweet spot,” Sun says. “It’s right before they start spawning in the wild.”
When the boats reach the release site, the team moves with such precision they act nearly as one. The first order of business is checking oxygen levels in the carboys to make sure there’s still plenty for the fish.
It’s now 10:05 am.
Current Delta smelt releases, which began in 2021, are small-scale experiments that test the nitty gritty of getting the fish from the conservation hatchery to their native habitat. Testing transport and release methods will help prepare the team for future large-scale releases to supplement the all but gone wild population. Sun is encouraged by the results so far.
The first year, the team released 55,733 hatchery Delta smelt in groups of 6,400 over the course of the winter. Each release entailed two back-to-back deliveries of 16 carboys collectively holding 3,200 fish. Every single fish had a clipped fin to let survey crews distinguish hatchery Delta smelt from wild ones at a glance. The goal was simply to see if hatchery smelt could withstand the perils of the Delta.
“That was the first important finding,” Sun says. “They can survive in the wild.” Hatchery smelt can also disperse from the release site. Surveys showed that the fish traveled north as far as the Sacramento River Deep Water Ship Channel and west as far as Suisun Marsh.
Last year―the project’s second―the team released 43,705 smelt. This time each group of 6,400 was tagged with a different color, bright enough to show through the fishes’ skin, so survey crews would know when they had been released. The goal was to see how long the fish lived in the wild.
Surveys showed that hatchery smelt survived up to two months, about as long as could be expected. Delta smelt typically live only one year, just long enough to spawn, and the released fish are near the end of their lifespan.
This year’s goals include fine tuning release methods. Yesterday, the release team opened the carboys directly to the river. A U.S. Geological Survey crew then tracked the smelt underwater with sonar to see if any were snapped up by bigger fish. Predation hasn’t been a problem so far but could become one in the future, as larger releases are more likely to attract striped bass and other non-native predatory fish.
“Striped bass are smart,” says CDFW biologist James Hobbs, who manages fish monitoring surveys in the San Francisco Bay-Delta, adding that these introduced fish quickly home in on hatchery salmon fingerling release sites and then lie in wait to chow down.
Today’s Delta smelt will start out in a 5-by-7-foot cylindrical cage made of perforated steel. The cage, designed by the UC Davis Fish Conservation Physiology Lab and field-tested by the California Department of Water Resources, is anchored to the river bed and equipped with two air tanks that keep it floating near the water surface.
The rationale is that this transition from hatchery to river will let the smelt acclimate to their new home, while also protecting them from predators and allowing water to flow through gently. As Sun OKs the oxygen levels in one carboy after another, her teammates quickly but carefully empty those she’s already checked into the cage in the river. There’s a sense of celebration when the 200 fish in the last carboy join the 3,000 already swimming in the submerged cage.
It’s now 10:45 am―well before the noon target for keeping the smelt safe during their journey from the hatchery to the river.
The team relaxes from all focus to easy banter as they greet a UC Davis crew standing by on another boat. The crew is here to fasten a top on the cage. Tomorrow, they’ll return to remove the top, let the air out of the tanks, and sink the 400-pound cage away from the fish. This lets the smelt stay together and swim into the river as a school.
Models suggest that saving Delta smelt in the wild will require supplemental releases of several hundred thousand hatchery fish each year. So, besides continuing to test release methods, the team also has a new goal. This winter they hope to double the total number of fish―from about 50,000 to 100,000―to get ready for larger releases.
More carboys is not an option as the team already has all they can handle at 32 per release. Instead, they’re trying something new: hauling smelt in cylindrical tanker trucks like those that transport fuel and milk. “That way we can increase the number of fish we release at once,” Sun says. “Right now we’re at 6,400 maximum and we’re hoping for tens of thousands.”
The team hopes to move beyond experimental releases to the larger supplemental releases in 2024. However, the conservation hatchery currently lacks the capacity to raise the hundreds of thousands of fish needed. The U.S. Bureau of Reclamation, which funds the facility, plans to expand it to help boost Delta smelt production by 2025.
More Delta smelt alone won’t be enough to save the species in the wild, however. “It’s just one piece of the puzzle,” Sun says.
Other pieces include ways of making the Delta a better home for these fish. UC Davis fish expert Andrew Rypel fears too many pieces may have been lost. “The Delta smelt is functionally extinct in the wild and there are multiple causes that are not being addressed,” he says, ticking off the dearth of habitat and food, the ascendance of invasive species, and the water that is saltier due to freshwater exports and warmer due to climate change.
Despite his skepticism, Rypel still supports hatchery releases aimed at saving Delta smelt in the wild. “If there’s ever a time to pull the ripcord and try something like this, it’s certainly now,” he says. “I’d rather lose a species by trying than just give up.”
Wetland ecologist Letitia Grenier likewise lays out the many pieces that historically made the Delta a good home for the smelt, and are now missing. But, she says, they don’t necessarily have to be put back in place all at once or in any particular order.
“There are so many problems that we need to fix more than one,” says Grenier, who until recently directed the San Francisco Estuary Institute’s Resilient Landscapes Program and now directs the Public Policy Institute of California’s Water Policy Center. “Conservationists have been asking for more freshwater flows but that hasn’t happened―at this point we need to do what we can.”
Grenier is heartened by the Department of Water Resources’ EcoRestore Program, which is on track to create more than 30,000 acres of wetlands in the Delta region. These habitats are rich in the zooplankton that make perfect fish food, while also giving little fish places to rest and escape predators. “Bringing wetlands back should help all the fish in the Delta,” she says.
Whether this new habitat will be enough to turn the tide for Delta smelt is an open question. “The Delta used to be a giant wetland but 98 percent of the tidal marsh is gone,” Grenier says. “Will restoring 5 or 6 percent help the smelt?”
Her question may not be answered for quite a while. Restoration projects already “take forever” to design, fund and permit, and the Delta has an added complication. Many islands there are deeply subsided, raising concerns that new tidal marsh will flood private lands. Addressing this flood liability delays restoration projects even further.
Sun, well aware of the challenges, remains undaunted. Her commitment to the Delta smelt extends beyond her professional mission of conserving wildlife for the nation. “For me, the Delta smelt is not the bald eagle or salmon, it’s the little guy,” Sun says. “You’ve got to stick up for the little guy.”
