/ 12 March 2021

South Africa’s freshwater fish face extinction

Clanwilliam Sawfin Driehoeks River Jeremy Shelton Lowres
Half a century ago, Clanwilliam sawfins thrived in most of the rivers draining South Africa’s spectacular Cederberg Wilderness Area. Today, this muscular rugged-finned freshwater fish is listed as ‘near threatened’ by the IUCN Red List, with just 11 riverine populations now remaining. Predation by invasive bass on young sawfins is the number one cause behind the recent population declines. (Jeremy Shelton)

Sarah Fransman remembers how, 30 years ago, Clanwilliam sandfish swirling in the Biedouw River Valley in the Cederberg looked like a golden, shimmering wave. “The whole school would stretch from one side of the river to the other,” she recalls in the Saving Sandfish project series. 

But that spectacle is no more.

Last month, a report by the World Wildlife Fund and 15 nongovernmental organisations and alliances, titled the World’s Forgotten Fishes, described how freshwater biodiversity is declining at twice the rate of that in the oceans or forests. About a third of freshwater fish species globally are threatened with extinction. Populations of migratory freshwater fish have plunged by 76% since 1970 and megafish by a staggering 94%. And 80 freshwater fish species are extinct. 

Thousands of species are threatened by habitat destruction, hydropower dams on free-flowing rivers, over-abstraction of water, pollution, mining and overfishing.

In the early 1990s, migrating sandfish were so plentiful in the Olifants-Doring River system that locals collected them by hand when they gathered to spawn, according to Jeremy Shelton, a freshwater conservation biologist at the nonprofit Freshwater Research Centre, which is leading the Saving Sandfish project. 

As the fish have disappeared, so have the recipes for curries, cakes and biltong. 

The sandfish is South Africa’s most threatened migratory freshwater fish. It’s so scarce that it’s known to spawn in only two small tributaries of the Doring River — the Biedouw and Oorlogskloof — and has disappeared from the Olifants River Catchment. The Doring River and its tributaries constitute the last large undammed, free-flowing river in the Cape Fold Ecoregion biodiversity hotspot.  

In some years, adults migrate up the Biedouw River to spawn. But when the hatchlings swim downstream, they are devoured by predatory alien, invasive fish such as the North American black bass and bluegill sunfish. 

“There is no next generation to replenish the older, ageing population,” says Shelton.

The Saving Sandfish project has rescued 610 juvenile sandfish and aims to retrieve 5 000 more by year-end. They will be put in temporary nurseries in dams cleared of alien species, where they can grow and become “bass-proof”.

Rivers, lakes and wetlands are among the most biodiverse places on the planet, home to half of all the world’s fish species. “Yet few people have any idea of the unimaginable diversity that swims below the surface of the world’s freshwater ecosystems or how critical these undervalued and overlooked freshwater fishes are to the health of people and nature around the world,” reads the WWF report.

Freshwater fishes are the aquatic version of the canary in the coal mine. “If our freshwater ecosystems deteriorate to the point where they can’t support a healthy population of fish, we can be sure they won’t be fit for humans either,” says the report.

In South Africa, freshwater fish are the most threatened of all species groups, with one in three facing extinction, according to the South African National Biodiversity Institute’s National Biodiversity Assessment.  

“Our freshwater species face a cocktail of interactive, synergistic threats. Water abstrac-tion and invasive species, climate warming and drought as well as invasive plants that suck rivers dry,” says Shelton, adding that invasive, alien fish have caused the biggest population declines of indigenous species.

“Conservation is all about people, and people are only going to look after an ecosystem if they care about it,” he says. “The first step to caring about it is knowing about it.”

Bending back the curve of biodiversity loss “hinges on freshwater awareness, compassion and advocacy”, says Shelton, who uses his films and photography to raise the profile of hidden freshwater ecosystems, celebrate their conservation heroes and inspire deeper connections between people and freshwater life. 

“Throughout the country, we’ve got these high levels of endemism, species that are unique to an area that don’t occur anywhere else, particularly in the Western Cape,” he says. 

Their fragile, narrow ranges make them vulnerable to human changes. 

Dewedine van der Colff, a Red List scientist at the threatened species unit at the Kirstenbosch Research Centre, says freshwater fish species in South Africa have experienced “many local extinctions (population extinctions). 

“The main threats identified from our recent national IUCN Red List assessment of freshwater fishes, was invasive alien fishes, pollution followed by natural system modification (for example, damming and water management).” 

At the provincial level, conservation agencies are trying different methods to control invasive alien fishes. “However, this is costly and they do not always have enough resources and human capital to control these species. Other threats are more at the landscape level and are difficult to mitigate.” 

Climate change is a potential future threat, especially in areas with current extensive water abstraction, where reduced rainfall could shrink available habitat for some species, she says.

A national freshwater fish specialist group has been established that includes taxonomists, ecologists and representatives from all provincial conservation agencies. 

“This group will guide and assist Sanbi in collaboration with the South African Institute for Aquatic Biodiversity  and other partners to bend the curve on further declines for freshwater fishes by identifying knowledge gaps and making sure that there is expertise in South Africa so that we can protect these species and prevent further losses,” she says.