The unprecedented effort to save one of Africa's most threatened fish - National Geographic

As winter begins in South Africa, the dry season ends, and rains return to the Western Cape province. Parched washes become streams again. Wildflowers bloom. And around August, Clanwilliam sandfish rush upstream to spawn en masse.

Or rather, that's what they used to do.

These torpedo-shaped, silvery fish—which get their name from a town in the area—were once were so numerous in this southwestern corner of the country that their reproductive pilgrimages roiled the tributaries of the Doring, a major waterway that rises in the interior before flowing into the mountains of the Cape.

A net survey that sampled fish in the Doring River (pictured above) revealed most were non-native species, such as bluegill sunfish—animals that prey on baby sandfish.

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Left: Two adult sandfish swim up the Biedouw River at night to reach their natal breeding grounds. This is the last known population of sandfish that migrates to spawn.

Right: Researcher Jeremy Shelton looks for sandfish eggs below a spawning riffle in the Biedouw. Eggs take up to 10 days to hatch into small fry. Conservationists raise these small fish in protected pools and re-release them to the wild once they've grown bigger.

"There were so many sandfish they would make a wave," recalls Sarah Fransman, who long has lived near the confluence of the Doring and a tributary called the Biedouw. "The whole school would stretch from one side of the river to the other."

In those days, Fransman would eat sandfish, as they were so plentiful as to be part of the cultural landscape. She even still has recipes for them. But those days are long past.

Today, sandfish are endangered, so much so that they're near the brink of extinction. Last year, fewer than 200 swam up the Doring and into the Biedouw to spawn, says Jeremy Shelton, a conservation biologist and National Geographic Explorer at the Freshwater Research Centre, in Cape Town. The Biedouw is the last known place where they undertake these reproductive migrations.

Sandfish (Labeo seeberi) can grow to two feet and mysteriously have the smallest scales of any freshwater fish, says Paul Skelton, a freshwater ecologist and professor emeritus at the South African Institute for Aquatic Biodiversity. Sandfish also have bottom-facing mouths for slurping detritus and algae on stream bottoms. (Their name in Afrikaans, onderbekvis, means "undermouth fish.") They play an important role in their ecosystem as consumers of organic matter and as prey for a variety of native creatures, such as African clawless otters.

That predator-prey balance has been upset because North American sportfish have been introduced into the area in recent decades. These invaders are a serious threat, gobbling up young sandfish, says Shelton, who grew up in Cape Town "splashing in coastal rock pools and following crabs and tadpoles in a small stream behind my family home."

Shelton says the sandfish's plight "literally keeps me up at night… but there's still hope."

He teamed up with another National Geographic Explorer, Otto Whitehead, an independent ecologist and filmmaker who is no less passionate about conservation (and fish) in his native South Africa. The pair had met in 2013 while working on a film about another beleaguered endemic species, the Breede River redfin.

In 2018, Shelton and Whitehead founded Saving Sandfish, a project funded by the National Geographic Society to rescue young sandfish from the Biedouw and raise them in predator-free ponds until they're about six inches long—large enough to better avoid being eaten—before releasing them back to their natal stream.

Aneri Swanepoel, an intern at the Freshwater Research Centre, and National Geographic Explorer Otto Whitehead rescue sandfish from the Biedouw River. After netting and placing fish in a bucket, they will take them to a sanctuary where the creatures can grow bigger.

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Left: The Cape Fold Ecoregion, through which the Doring River flows, is home to a diverse range of geographically isolated rivers that are hotspots for freshwater biodiversity. Many of its fishes, invertebrates, and amphibians are found nowhere else of Earth.

Right: Bluegill sunfish, native to North America, have wreaked havoc after being introduced to South African rivers. Unlike any native predator, they easily gobble up large amounts of young sandfish.

Saving Sandfish is an unprecedented freshwater conservation project for the continent. Already, says Skelton, who isn't involved in the project, it has improved the survival prospects for this imperiled fish.

So far, the team has caught 15,000 juvenile sandfish and begun raising them in protected ponds with the support of Western Cape landowners. Since September 2021, the team released nearly 1,300 back into the Biedouw. The hope is that they'll return to the Doring and migrate back upstream to spawn in the Biedouw the following year, Shelton says.

It's possible that sandfish could be ready to spawn when they're two years old. To find out, the conservationists inserted tiny tags into nearly a thousand of the fish, which will allow researchers to track their migrations and spawning behavior. These tags stay in the fish's bodies for the rest of their lives and have an internal microchip containing a unique barcode that is recorded when it passes close to a special antenna.

Threatened fish

The Doring and the major river it eventually flows into, the Olifants, drain a vast region of the Western Cape, and are home to an unusually high concentration of unique and threatened species. Five of the 11 species endemic to the area are considered endangered or critically endangered.

These species, including the sandfish, have dwindled for several reasons. Recent drought years partially related to climate change have drastically reduced river flows. Researchers predict that the already water-stressed Western Cape region will experience further reductions in river levels as temperatures rise up to four degrees Fahrenheit higher during the next 50 to 100 years.

For most of the year sandfish live in isolated pools along the Doring River. But every spring they migrate up tributaries such as the Biedouw River, shown here, in search of suitable riffles in which to spawn.

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Left: Several adult sandfish lock themselves in an embrace during their annual spawning ritual in the Biedouw. As the sun sets, the fish start flirting and becoming more active, rubbing alongside each other and darting forth, eventually releasing eggs and sperm.

Right: An adult female sandfish may release up to 30,000 eggs in a single spawning season. Males fertilize these by releasing clouds of sperm, or milt.

At the same time, farmers are extracting water to irrigate crops such as rooibos and plants to feed livestock. Another challenge are non-native, water-hungry trees—black wattles, eucalyptus, poplars—that have taken hold in the valley of the Biedouw and elsewhere. During the past decade, CapeNature, the regional conservation authority, has been clearing black wattle and poplar infestations in the upper Biedouw. But large areas of invasive plants must still be removed to help mitigate their drawdown of river waters, Shelton says.

On top of all this is the presence of those hungry sportfish. Beginning around the 1940s, anglers seeded the Doring, Olifants, and other nearby rivers with bass and bluegills, not realizing the ecological consequences of doing so. Within the range of the sandfish, today there are only a few streams without voracious exotic fish: Small stretches of the upper Biedouw and the nearby Oorlogskloof. Both are shielded from invasion by low, rocky waterfalls—and both are home to non-migratory populations of sandfish.

The only known remaining migratory population lives in the Doring, spending the summer in isolated, rock-bottomed pools. During the rainy reason, the Doring and Biedouw fill and resume flowing, allowing the fish to swim upstream to spawn and lay eggs. Until about 2010, when a decade-long drought set in, the Biedouw held significantly more water through the summer months, including in predator-free pools that the project's protected sanctuaries are meant to mimic.

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Left: Sandfish have complex nostrils, or nares, that help them sniff out predators and direct their migration back to their natal streams. They are a member of the Cyprinid fish family, which made its way to Africa when the continent collided with Eurasia about 20 million years ago.

Right: Fertilized eggs that settle in well-oxygenated gaps between rocks will emerge into tiny sandfish after five to 10 days. Those that end up on sandy areas will most likely be eaten or not develop properly. These rocky stretches are crucial for sandfish reproduction.

A sandfish embryo developing within an egg.

But today the Biedouw stops flowing around January, and dries up between February and May. During these months, young sandfish are easy pickings for bass and bluegills—or run out of water.

"Their life cycle is broken," Whitehead says—hence the plan to release sandfish when they are big enough to avoid predation.

Connecting with local people

Working with local people and making them aware of the importance of sandfish to the freshwater ecosystem is key to the ongoing success of Saving Sandfish.

Whitehead and Shelton have approached Western Cape landowners and asked them to allow sandfish to mature on their properties in small ponds. So far, Saving Sandfish has established five such reservoirs on private land.

In late 2020, Whitehead, Shelton, and a rotating group of locals began capturing young sandfish from the Biedouw that had hatched just after the September spawning. They netted the fish and transported them in buckets to the reservoirs.

"Landowners take pride in their sandfish sanctuary dams, narrowing the gap between people and life beneath the surface and setting the stage for reimagining our relationship with water," Shelton says.

After being taken from the Biedouw River, young sandfish are released into a sanctuary free of exotic predatory fish. Here they can safely grow until they reach a "bass-proof" length over six inches. Then they can be released back to the wild.

One of those landowners is Lauren Bradley, who moved to the Biedouw Valley with her husband and two sons in 2017 to start Enjo Nature Farm, an ecotourism attraction, and give their boys a rural upbringing. When Whitehead and Shelton proposed raising sandfish on their property, Bradley was impressed by their sincerity. "I knew at that moment that we had to be absolutely wholeheartedly committed to this project," she says, adding that the whole family has been helping with the sandfish rescues.

To date, Saving Sandfish has brought nearly 3,000 fish to the reservoir on the Bradley property. Nearly 500 at "bass-proof size" have been put back into the Biedouw, Shelton says.

"It's a paradigm shift for the local communities to be aware of and concerned for the fish," says Paul Skelton, of the South Africa Institute for Aquatic Biodiversity. "In that respect, Jeremy and his team have been terrifically successful."

'Disbelief, then joy, pure joy' 

Saving Sandfish also supports and conducts scientific research. In September 2020, Shelton, Whitehead, and Cecilia Cerrilla, a doctoral student at University of Cape Town, finally documented sandfish spawning.

After many days of waiting, Shelton says he felt "disbelief, then joy, pure joy," when they saw sandfish congregating and spewing forth sperm and eggs. These fish are "just so rare these days, and no one has seen sandfish spawning for decades," he says.

A scientist releases juvenile sandfish back into the wild after nearly a year living in a sanctuary pool. In 2021, more than a thousand young sandfish were put back into the Biedouw, making it Africa's largest freshwater fish rescue and release in history.

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Left: Young sandfish swim in an isolated pool in the Biedouw. With water levels dropping, making them more vulnerable to predators (and drying out), their only chance of survival is human intervention.

Right: The San people, who once lived in Western Cape, created this rock art. It may depict sandfish, one of the many species—and an important food source—that once teemed in the region's rivers.

Around that time, the team began filming sandfish with a 360-degree camera. "It's transformed the way I see fish," Whitehead says. This filming revealed, for example, the toll the migration takes, leaving marks and scars on their fine-scaled bodies. The conservationists also came to see that each fish has its own personality.

"When you spend time with them underwater, you quickly realize that these are individuals," Shelton says. "Some seem youthful, playful, energetic. Others are calm and composed, almost zen-like, so comfortable and confident in the face of uncertainty."

"Now I'm head over heels for sandfish—because I've met them," Whitehead adds.

As part of her PhD thesis on sandfish, Cerrilla is conducting a survey of all their known populations, and she hopes to find more. Soon, she'll scout other rivers to see if sandfish are still spawning elsewhere, including in the Tra-Tra, a tributary south of the Biedouw.

The Clanwilliam sandfish is "an ambassador for the whole river system in a way that no other fish is," Cerrilla says.

"It represents the health of a whole freshwater ecosystem, and the connectivity."

Once the sandfish arrive in the Biedouw River, they wait weeks for the perfect conditions—such as ideal water temperatures—to spawn, as seen above.

EDITOR'S NOTE: The National Geographic Society, committed to illuminating and protecting the wonder of our world, funded the work of Explorers Jeremy Shelton and Otto Whitehead. Learn more about the Society's support of Explorers highlighting and protecting critical species.