Sarah Fransman remembers when spawning Clanwilliam sandfish arrived in the Biedouw Valley near Clanwilliam. The thousands-strong shoal creating wavelets along the surface of the Biedouw River, fish packed on top of one another, Fransman said. “Dit was wonderlik om dit te sien in die water.” (It was wonderful to see it in the water.) Now the fish are scarce.
Fransman’s memory reaches far back, as does local farmer Willem van Zyl’s. Tramping down the dry riverbed, on the family farm in the Oorlogskloof River Valley near Vanrhynsdorp, he points to a juncture of dark rock where the Oorlogskloof River, a tributary of the Doring River, flowed fast for two or three months of the year after winter rains, and the spawning fish migrated upstream in August and September each year. Locally known as “onderbekvis” to describe a “down-turned hoover-like mouth”, they were abundant then, said Van Zyl.
“The Oorlogksloof River still flows in the winter and spring, but fewer pools remain through the summer, about half as many remain through the summer compared to before 2015 when the drought set in,” said Cecilia Cerrilla, a University of Cape Town (UCT) PhD candidate.
Multi-faceted rescue campaign
Fransman and Van Zyl feature in a new documentary series, Saving Sandfish, a 10-part web series produced by Dr Otto Whitehead and Dr Jeremy Shelton, part of a National Geographic Society-funded programme of conservation, engagement and research to preserve one of the country’s most threatened large-bodied freshwater fish.
Supporting this multifaceted programme is a research initiative spearheaded Cerrilla. Her focus is on the added threat of invasive fish species to the sandfish’s remaining habitats.
It’s a worldwide problem highlighted by a research paper on which she is lead author. Titled “Rapid population decline in one of the last recruiting populations of the endangered Clanwilliam sandfish (Labeo seeberi): The roles of climate change and non-native fish”, the paper draws on her master’s research in the Department of Biological Sciences at UCT and has been published in Aquatic Conservation: Marine and Freshwater Ecosystems.
Three non-native fish species are found in the Oorlogskloof River, home to one of the last recruiting populations of sandfish. These are smallmouth bass (Micropterus dolomieu), bluegill sunfish (Lepomis macrochirus) and banded tilapia (Tilapia sparrmanii).
Tilapia and sunfish were introduced to local rivers as fodder fish for bass, which were introduced to the Olifants/Doring River system in the 1930s as a sportfish, said Cerrilla. But the bass and sunfish have had a catastrophic impact on young sandfish.
Invaluable data sets
Cerrilla’s major contribution to the conservation project has been on the research side. For her recent paper she analysed an “incredibly” valuable six-year data set collected over nine years across 25 km of the Oorlogskloof River. The figures are alarming, showing a 92.6% decline in the relative abundance of sandfish between 2013 and 2018, precipitated by a 99.6% decline in young-of-the-year individuals.
“A combination of extreme rainfall events and drought appear to have played a key role in the decline and subsequently prevented recovery,” said Cerrilla.
Her study showed that small sandfish were almost entirely absent from the ‘invaded’ section of the Oorlogskloof but relatively abundant where the non-native species were absent. Improved water resource management and limiting the spread of non-natives must be conservation priorities, she said.
Taking fish to water
With the cooperation of local landowners and conservation bodies, human chains can be seen at dams moving white buckets of sandfish along, from bakkie to water.
“We’ve recruited five sanctuary dams now at four different properties, close to the Biedouw River in the catchment area,” said Cerrilla.
Filling in missing habitat
“But in the end, we’re going to have to do something about the alien fish and the water. “Localised eradications must be considered. And it’s already happen[ing] where alien fish have been cleared from a 4 km stretch of the Rondegat River in the Cederberg, which is home to three native fish species.”
This is the first section of a South African river to be rehabilitated through the removal of invasive fish using the piscicide rotenone.
“It’s complicated, but it’s not impossible,” said Cerrilla.
There is hope. In wet years tiny sandfish have been spotted in the shallow pools along the Biedouw River, she said. Last year she carried out extensive walking surveys during spawning season in September to document the migration.
“We saw around 180 adult fish migrating up the Biedouw and witnessed several spawning events. It’s great news that some sandfish are still returning to spawn.”
Conservation must also involve farmers and landowners on the water abstraction issue, Cerrilla said.
“We don’t have the silver bullet at this point. But we are starting with the sanctuary dams and reading the situation from there.”
And the future generations of Fransmans and Van Zyls may yet witness massive “onderbekvis” migrations when the surface of the Doring River agitates with the energy of fish swimming upstream to continue a vital cycle of life.
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