Saving South Africa’s most threatened migratory freshwater fish, the Clanwilliam sandfish
All images by Jeremy Shelton and Otto Whitehead
The tea-stained waters of the Biedouw stir and glint as the first Clanwilliam sandfish fin their way up into this seasonal tributary after months of lying low in Doring River mainstem. Moving slowly upstream in groups of 10-20, these magnificent fish are on an age-old quest to reach their spawning grounds.
Adult sandfish migrate up the Biedouw River to spawn in spring.
It’s late August in the Cederberg Mountains, a wilderness area a few hours’ drive from Cape Town, and a hotspot for South Africa’s endemic freshwater fishes. The Biedouw River, which drains the Cederberg’s north-east flanks is swollen following an onslaught of rain-bearing cold fronts and Karoo-born thunder storms, but now as winter turns to spring, the water slowly starts to warm and subside. It’s these shifts in water temperature and flow that trigger the spawning migration of the Clanwilliam sandfish Labeo seeberi – South Africa’s most threatened migratory freshwater fish.
The moment of fertilization during sandfish the spawning ritual.
Stories from elders in the valley and paintings on the walls of caves allude to past sandfish migrations of epic proportions. “There were so many sandfish they would make a wave, the whole school would stretch from one side of the river to the other” recounts Sarah Fransman, who has lived in the Biedouw all her life, “But that is no more”. Today the sandfish spawning migration in the Biedouw comprises less than 200 fish.
Rock art in the Cederberg mountains depicting human forms and fish that resemble sandfish.
Today sandfish numbers have dropped so low that the species has been listed as Endangered on the IUCN Red List, and considered to be in a state of continued decline. “It’s a cocktail of threats that have driven the sandfish populations to such low levels” explains Dr Jeremy Shelton, a freshwater conservation biologist at the Freshwater Research Centre, and project leader on an IUCN SOS-funded project aimed at saving this species from extinction. After they spawn, thousand of young sandfish hatch from clusters of eggs littering the stream bed. But these young sandfish will not survive their first summer. They are heavily preyed upon by black bass and bluegill sunfish – predatory sport fish introduced from the United States. “Even those sandfish that do manage to escape predation don’t survive because they run out of water after a few months” says Shelton. Historically the Biedouw River held water year-round, but today it dries up completely due to over-abstraction and infestations of thirsty invasive plants.
Invasive bluegill sunfish pose a serious threat to the survival of young sandfish.
Over abstraction of water and thirsty invasive plants cause the Biedouw River to dry up completely in summer, leaving young sandfish stranded.
“This recruitment failure year after year is a recipe for extinction” explains Cecilia Cerrilla, a PhD student working on the project, and that’s where the SOS-funded “Saving Sandfish” project is working to make a difference. “By rescuing young (5 cm–long) sandfish from dangerous habitats and relocating them to the safety of farm dams from which alien fish have been cleared with the help of supportive land owners, we hope to safeguard the species from extinction and ultimately boost their numbers in the wild” adds Shelton.
PhD students Cecilia Cerrilla and Mohammed Kajee survey sandfish in one of the sandfish sanctuary dams.
Over the last two summers, the project team comprising scientists, conservationists, land owners, community members and students have collectively rescued over 15,000 young sandfish, making this conservation effort Africa’s biggest ever freshwater fish rescue! “I’m extremely proud of what we have achieved here” exclaims Shelton, but there is still much to be done to ensure the survival of the species.
Community members from Heuningvlei settlement near the headwaters of the Biedouw River assist with the 2021 sandfish rescue.
Film maker and conservation biologist Dr Otto whitehead lifts buckets of young sandfish into the back of a vehicle for transport to a sandfish sanctuary dam.
Part of the 2021 sandfish rescue team comprising students, scientists and community members.
Once the fish in the dams reach a bass-proof size of 20 cm they will be released back into the river in the hope of boosting population numbers in the wild. “The hope is that these fish will return to the Biedouw to spawn, and if that happens we’ll know our conservation interventions have been a success” says Cerrilla. To track the survival and spawning of the dam-reared fish in the wild, the project team are marking the fish using tiny PIT tags (each with a unique barcode) prior to release. This September they will also be installing a PIT tag antenna (which will detect any tagged fish that swim over it) on the stream bed to record whether any of these fish return to their natal stream to spawn.
A 20 cm-long sandfish reared in one of the sanctuary dams is released back into the wild after being marked with a PIT tag.
A PIT tag with its unique barcode. By tagging fish the team will be able to determine whether fish released from the sanctuary dams return to the Biedouw River to spawn.
Once the short-term survival of the species is secured through the rescue-rear-release interventions, Shelton and the project team have plans to address root causes of the sandfish population crash, and declines in other endemic freshwater fishes of the region. “For these efforts to be sustainable, we need to reduce the impacts of predatory invasive fish and thirsty invasive plants by clearing them from priority catchments like the Biedouw” remarks Shelton enthusiastically “and to achieve this we must work closely with the land owners and local communities”.
The Biedouw River valley in Springtime.
The Saving Sandfish project is supported by IUCN Save Our Species, co-funded by the European Union.
To find out more about the project, watch the Saving Sandfish web series here.