A mass die-off of sardines along South Africa’s west and south coasts this month has prompted investigation into possible causes, including a herpesvirus strain detected in the affected fish. The event, which has resulted in large numbers of dead and dying sardines washing ashore, has attracted concern from scientists and impacted local infrastructure.

Pilchard herpesvirus (PHV), a virus related to human herpes but not transmissible to humans, has been identified in the sardines. This virus was previously linked to similar mass mortality incidents in Australian sardine populations during the 1990s. The current outbreak coincided with operational challenges at South Africa’s sole nuclear power facility, where a reactor had to reduce power output by half after dead sardines blocked a valve.

While PHV detection provides a potential explanation for the mortality event, researchers caution that multiple factors may have contributed. Harmful algal blooms and unusually cold sea temperatures are also under consideration as possible stressors leading to the mass deaths. Biologist Dalene Vosloo noted that the event’s complexity suggests several environmental elements could be involved.

The sardine die-off is notable due to the economic and ecological importance of the species in the region. Sardines form a key part of the marine food web and support fisheries vital to local communities. As investigations continue, authorities and scientists are monitoring the situation closely to understand the causes and assess the broader impact on marine ecosystems and human activities.