Scientists jump in as alien invaders threaten to leave sandfish ...

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Hundreds of fish moved to 'safer' waters

Scientists jump in as alien invaders threaten to leave sandfish up creek

Unusual project aims to save the iconic freshwater species that used to spawn en masse like salmon

Senior reporter
Sandfish migrate up the Biedouw River in the Cederberg to spawn in spring.
Brighter future Sandfish migrate up the Biedouw River in the Cederberg to spawn in spring.
Image: Jeremy Shelton

A team of SA scientists has rescued hundreds of endangered freshwater fish and moved them to a 1km stretch of remote river protected by a waterfall – where alien fish can’t eat them.

The unusual project, dubbed Saving Sandfish, is the latest effort aimed at saving the migratory Clanwilliam sandfish, a species so rare it is known to spawn in only two small tributaries in the Cederberg – nothing like the old days when it spawned en masse like salmon and could be scooped out of rivers at will. It even features in ancient rock art.

The fish is remarkable for its thick lower lip – locally it is called an onderbek – that sucks up algae and slime. Species extinction could therefore affect the ecology of the Doring River by resulting in a build-up of the fish’s former food.

Project leader Jeremy Shelton, a researcher at the  Freshwater Research Centre in Cape Town, said the spread of alien fish had all but wiped out sandfish in their natural habitat.

In spring, the eruption of flowers in the Biedouw Valley coincides with the migration of adult sandfish, which move up from the Doring River to spawn.
FISHY HEAVEN In spring, the eruption of flowers in the Biedouw Valley coincides with the migration of adult sandfish, which move up from the Doring River to spawn.
Image: Otto Whitehead

“The young fish don’t survive because they are under a lot of pressure, preyed upon heavily by invasive fish like bass and bluegill,” and Shelton.

“At the moment the species is on the edge of extinction as a very small number of wild sandfish are left and there is almost no recruitment coming through. So there is this ageing population that is struggling to replenish itself.”

An additional threat is water scarcity, with rivers drying up or turning into a series of small, isolated pools where young sandfish are easily devoured by predators. 

Bruce Paxton of the Freshwater Research Centre releases four of the 610 young sandfish that were rescued in October 2019.
Helping hand Bruce Paxton of the Freshwater Research Centre releases four of the 610 young sandfish that were rescued in October 2019.
Image: Jeremy Shelton

The rescue mission in October 2019 involved relocating 610 two-month-old sandfish to a 900m stretch of the upper Biedouw River which is free of invasive fish and has water year round. “We will be going back later this year to see how well that worked,” Shelton said.

The Saving Sandfish team are also working with farmers in the area who are volunteering their dams as sandfish sanctuaries, once cleared of alien fish.

Barry Lubbe, owner of Mertenhof Farm in the Biedouw Valley, removes an invasive bluegill sunfish from his dam to create a sanctuary for young sandfish.
BODY SNATCHER Barry Lubbe, owner of Mertenhof Farm in the Biedouw Valley, removes an invasive bluegill sunfish from his dam to create a sanctuary for young sandfish.
Image: Jeremy Shelton
The invasive bluegill sunfish is a voracious predator of juvenile sandfish. This 13cm bluegill had a 5cm sandfish in its stomach.
Balancing the scales The invasive bluegill sunfish is a voracious predator of juvenile sandfish. This 13cm bluegill had a 5cm sandfish in its stomach.
Image: Otto Whitehead

“Once they [the sandfish] are big enough, they will be released back into the wild so they’ll have a chance to hopefully one day spawn themselves, and in that way we hope to help boost populations of sandfish, and avoid the extinction of this iconic freshwater fish,” Shelton said.

Writing in a fisheries blog, Shelton said the Saving Sandfish project aimed to rescue a further 5,000 young sandfish and release them into other sanctuaries.

An adult Clanwilliam sandfish in the Biedouw River.
Up the creek An adult Clanwilliam sandfish in the Biedouw River.
Image: Jeremy Shelton

The species’ plight was in stark contrast to its former abundance, he said.

“In the early 1990s sandfish were so plentiful in the Olifants-Doring river system of SA that locals collected them from the river by hand when they gathered en masse to spawn.

University of Cape Town master's student Cecilia Cerrilla with young sandfish rescued from the Biedouw River.
Future in her hand University of Cape Town master's student Cecilia Cerrilla with young sandfish rescued from the Biedouw River.
Image: Jeremy Shelton

“They used the fish to make curries, fish cakes and biltong. However, these recipes have since vanished from the lives of those that live in the valleys once frequented by sandfish.”

The former mass migrations now exist only as memories, and in the rock art of indigenous San people who thrived in the Cederberg thousands of years ago, Shelton said, but “through the combined efforts of scientists and land owners there is renewed hope that the sandfish and their freshwater habitats can be saved”.

University of Cape Town master's student Cecilia Cerrilla searches for juvenile sandfish in the lower Biedouw River, where they are vulnerable to predation by alien fish.
wading in  University of Cape Town master's student Cecilia Cerrilla searches for juvenile sandfish in the lower Biedouw River, where they are vulnerable to predation by alien fish.
Image: Jeremy Shelton

Shelton has co-founded a freshwater storytelling collective called Fishwater Films with Dr Otto Whitehead. Find out more about the project in their latest YouTube series Saving Sandfish.

Shelton is also raising funds for his sandfish project. Anyone  wishing to donate can do so here.