How geneticist Dr Sihle Mthethwa's research aims to save the Cape snoek from extinction

A study conducted by a geneticist from the Stellenbosch University (SU) highlights the vulnerability of the popular Cape snoek and offers ways to address it. 

The Cape snoek is one of South Africa’s most important fish species. 

It is not just a staple for many but for those in low-income households, it is a lifeline in small-scale fishing communities. 

But, years after stable catches, snoek is now more vulnerable than it appears. Declining catches have put pressure on local fishers and opened the door to imports from New Zealand. 

The importation has raised concerns about the future of local fisheries and the survival of coastal livelihoods that depend on them. 

Dr Sihle Mthethwa from the Department of Genetics, said his study suggests ways to address the vulnerabilities faced by the Cape snoek. 

According to Mthethwa, by analysing the fish’s genetic makeup, he found that snoek populations are split into distinct groups that do not mix freely, both globally and along South Africa’s coastline. 

“This challenges the idea that Cape snoek is a single, resilient resource. Instead, it emphasises the need for careful, locally tailored management to protect this iconic fish – and the communities that depend on it – for the future,” Mthethwa said. 

He collected samples from multiple regions across the southern hemisphere including South Africa, New Zealand, Chile, and remote islands. 

Mthethwa used molecular tools to analyse their DNA to understand the evolutionary history, long-term population patterns, recent gene flow and population structure of snoek. He also compared samples from South Africa across different time periods.

“The DNA analyses reveal that Cape snoek in South Africa comprises of at least two genetically distinct groups that do not interbreed freely despite sharing the same location at the same time, with a possible third stock shared with Namibia,” Mthethwa said. 

“There is also evidence of a recent genetic bottleneck, meaning genetic diversity and numbers have declined in recent generations. This loss of diversity can make the species less able to cope with environmental change and fishing pressure.” 

In his study, Mthethwa said he tried answering three main questions: 

• Are Cape snoek from South Africa and barracouta snoek from New Zealand the same species? 
• How connected are Cape snoek populations across the Southern Hemisphere, and how has their evolutionary history shaped this connectivity? 
• Is the Cape snoek population within South Africa genetically uniform, or are there multiple distinct stocks?

“Verifying species identity can help prevent imported New Zealand barracouta from being mislabelled as South African snoek, protecting consumers and improving transparency in the fisheries trade,” Mthethwa explained. 

“Insights into the connectivity and evolutionary history of Southern Hemisphere snoek/barracouta are critical for fisheries management, making it possible to distinguish between a single, well-mixed population and distinct stocks, and preventing the overexploitation of local or isolated populations erroneously assumed to be part of a single global stock.

“Knowing that the Cape snoek population within South Africa is genetically uniform can help prevent overfishing of local subpopulations mistaken for a single, well-mixed population, enable targeted quotas, and support sustainable management,” Mthethwa said. 

He pointed out that Cape snoek catches were relatively stable historically, but have declined noticeably in recent years. As a result, local supply has become unreliable, increasing dependence on New Zealand-imported barracouta (the same species), which is often sold as ‘Cape snoek’. 

Mthethwa said the drop in catches raises concerns about overfishing, loss of genetic diversity, and the long-term sustainability of local populations. It also threatens the income and food security of communities that rely on the native fishery.

According to Mthethwa, it’s problematic if different snoek populations are treated as one stock because this can obscure the overexploitation of individual groups. 

“When the gene flow between fish populations is restricted, they struggle to replenish their numbers and genetic diversity from overfishing. This increases the risk of local collapse, a loss of unique adaptations, and long-term damage to fisheries and communities that depend on it, even when overall catch levels seem sustainable,” he said. 

Mthethwa called on those in the management and conservation of Cape snoek to recognise multiple genetic stocks rather than a single population; adjust catch limits and conservation measures to protect each stock individually; incorporate genetic monitoring into routine stock assessments; and be cautious about imports and labelling, as imported snoek does not serve the same ecological or economic role as local stocks.

Mthethwa said these changes could help prevent further genetic erosion and support long-term sustainable fishing. 

“Sustainable management must be based on genetic evidence, not just catch numbers, to protect Cape snoek for future generations,” he added. 

robin.francke@iol.co.za

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