For generations, Cape snoek (Thyrsites atun) has been more than a fish along South Africa’s coastline. It is a cultural staple, a source of livelihood, and an important contributor to food security, particularly in coastal communities of the Western Cape.

While public discussion has sparked some debate (on recent article in Cape Argus) , this research is not about restricting fishing, but about improving our biological understanding of a species that holds deep economic and cultural value.

Now, new research from the Department of Genetics at Stellenbosch University is helping to deepen our understanding of this iconic species. Rather than challenging the fishing industry, the study provides a critical biological perspective on how snoek populations are structured and connected.

Behind this work is Dr Siphesihle Mthethwa, a recent PhD graduate whose journey reflects both scientific dedication and personal resilience. From this PhD, he has produced two peer reviewed international publications, including work on the mitochondrial genome of Cape snoek , strengthening the scientific foundation of his findings and establishing him as a an emerging expert in marine genetics.

A journey of perseverance and purpose

Originally from Umzumbe, near Port Shepstone on the south coast of KwaZulu Natal, Dr Mthethwa began his academic journey at the University of KwaZulu Natal. In 2019, he started his PhD in Genetics at Stellenbosch University within the Molecular Breeding and Biodiversity research group, under the supervision of Prof Rouvay Roodt Wilding and Prof Aletta Bester van der Merwe.

What makes this achievement particularly noteworthy is that he completed his PhD part time, while working as a Technical Officer managing two research laboratories within the department. 

Balancing research, laboratory responsibilities, and personal commitments over several years, he graduated in 2025. This milestone is not only significant for him, but also for his family, whose support played an important role throughout his journey.

Looking beneath the surface: what the genetics reveals

Using advanced molecular tools, Mthethwa analysed both mitochondrial DNA and nuclear markers to investigate snoek populations across the southern hemisphere, including South Africa, New Zealand, Chile, and surrounding ocean systems.

The study revealed that Cape snoek and New Zealand barracouta are the same species. However, populations are not fully mixed and instead show clear genetic structuring. Within South Africa, at least two reproductively distinct groups were identified.

These findings suggest that while snoek is often treated as a single resource, it is biologically more complex, with different populations potentially responding differently to environmental conditions.

What this does and does not mean

Importantly, this research is not a fisheries stock assessment and does not attempt to make economic or policy conclusions. The research does not claim definitive declines or prescribe management actions, but rather identifies biological patterns such as population structure, connectivity, and changes in genetic diversity over time.

As Dr. Mthethwa explains:

“Genetic data reflects long term biological patterns such as connectivity, diversity, and historical population changes. It does not replace fisheries data, but adds an important layer of understanding.”

These insights are intended to contribute to a broader, more informed conversation that includes scientists, industry, and coastal communities.

Science in service of people and communities

At its core, this research improves our understanding of a species with both ecological and social importance. For Dr Mthethwa, the work reflects a journey from the KwaZulu-Natal coast to contributing internationally relevant science.

By combining rigorous research with real-world relevance, this study supports more informed discussions about the future of Cape snoek and the communities that depend on it.

 

Your departmental scribe

M. Le Roux