Sarah Fransman recalls the arrival of the Clanwilliam sandfish spawn in the Biedouw Valley near Clanwilliam. The shoal of thousands creates ripples on the surface of the Biedouw River, with fish piled on top of each other, Fransman said. “It was wonderful om dit te sis in the water.” (It was wonderful to see him in the water.) Now the fish are rare.
Fransman’s memory goes back a long way, as does that of local farmer Willem van Zyl. Walking on the dry riverbed at the family farm in the Oorlogskloof River Valley near Vanrhynsdorp, he points to a dark rock junction where the Oorlogskloof River, a tributary of the Doring River, flowed rapidly for two or three months of the year after winter. rains and spawning fish migrated upstream in August and September each year. Known locally as “onderbekvis” to describe a “downturned vacuum cleaner blocked”they were abundant then, says Van Zyl.
“The Oorlogksloof River still flows in winter and spring, but there are fewer pools left during the summer, about half less during the summer compared to before 2015 when the drought set in,” Cecilia Cerrilla said. , from the University of Cape Town (UCT ) PhD student.
Multi-faceted rescue campaign
Fransman and Van Zyl feature in a new documentary series, Save the Sandfisha 10-part web series produced by Dr Otto Whitehead and Dr Jeremy Shelton, as part of a Conservation, engagement and research program funded by the National Geographic Society to preserve one of the country’s most endangered large freshwater fish.
This multifaceted program is supported by a research initiative led by Cerrilla. It focuses on the additional threat of invasive fish species to remaining sandfish habitats.
It’s a global issue highlighted by a research paper of which she is the lead author. Entitled “Rapid population decline in one of the last recruiting populations of the endangered Clanwilliam sea cucumber (Labeo Seeberi): The roles of climate change and non-native fish”, the article is based on his MSc research in the Department of Biological Sciences at UCT and was published in Aquatic Conservation: Marine and Freshwater Ecosystems.
Three species of non-native fish are found in the Oorlogskloof River, which supports 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 forage fish for bass, which were introduced to the Olifants/Doring River system in the 1930s as sport fish, Cerrilla said. But bass and sunfish had a devastating impact on young sea cucumbers.
Cerrilla’s main contribution to the conservation project has been on the research side. For her recent article, she analyzed an “incredibly” valuable six-year dataset, 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 sea cucumbers between 2013 and 2018, precipitated by a 99.6% decline in young of the year.
“A combination of extreme rainfall and drought appears to have played a key role in the decline and subsequently prevented recovery,” Cerrilla said.
His study showed that small sandfish were almost entirely absent from the “invaded” section of the Oorlogskloof but relatively abundant where non-native species were absent. Improving water resource management and limiting the spread of non-natives must be conservation priorities, she said.
Take the fish to the water
With the cooperation of local landowners and conservation organizations, human chains can be seen on the dams moving white buckets of sandfish from bakkie to water.
“We have now recruited five sanctuary dams on four different properties near the Biedouw River in the watershed,” Cerrilla said.
Fill in the missing habitat
“But in the end, we’re going to have to do something about the alien fish and water. “Local eradications should be considered. And it’s already happened[ing] where exotic fish have been eliminated from a 4 km stretch of the Rondegat river in the Cederberghome 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,” Cerrilla said.
There is hope. In wet years, tiny sandfish have been spotted in the shallow pools along the Biedouw River, she said. Last year, she conducted extensive surveys on foot during the spawning season in September to document migration.
“We saw around 180 adult fish migrating to the Biedouw and witnessed several spawning events. It’s great news that some sea cucumbers are still coming back to spawn.
Conservation must also engage farmers and landowners on the issue of water catchment, Cerrilla said.
“We don’t have the miracle solution at this stage. But we start with the sanctuary dams and read the situation from there.
And future generations of Fransmans and Van Zyls might still witness mass ‘onderbekvis’ migrations when the surface of the Doring River stirs with the energy of fish swimming upstream to continue a vital life cycle.
Funders of the project include the National Geographic Society, the Mohammed Bin Zayed Species Conservation Fund, IUCN Save Our Species (co-funded by the European Union), the Ford Wildlife Foundation and the Rufford Foundation. Partners include Fynbos Fish Trust, CapeNature, North Cape Department of Environment and Nature Conservation, Mount Ceder, Bushmans Kloof, Enjo Nature Farm, Driehoek Guest Farm, South African Anglers Federation fly (FOSAF), Investec and Caleo Capital.