Scientists in South Africa are investigating a herpes virus as a potential cause for the recent mass die-offs of sardines along the country's west and south coasts. This marks the first time pilchard herpesvirus (PHV) has been identified in sardines off the South African coast. The virus was previously associated with two mass sardine mortality events in Australia during the 1990s.
The South African Department of Forestry, Fisheries and the Environment stated that PHV can cause inflammation and thickening of a sardine's gills, impeding its ability to absorb oxygen. Sardines and pilchards are the same species, with sardines being the younger stage. The department has clarified that PHV is a fish-specific virus and does not pose a known risk to human health, meaning commercially caught sardines and canned products remain safe.
Initial findings from the South African Institute for Aquatic Biodiversity and a local university, which are examining dozens of affected fish, indicate consistently high levels of PHV in dead specimens from the mortality events. Live fish examined showed varied levels of the virus.
While other factors such as harmful algae blooms, unusually cold sea temperatures, or low oxygen conditions were considered, the environment department noted that evidence increasingly points to PHV as the primary explanation. However, Dalene Vosloo, a biological sciences lecturer at South Africa's University of KwaZulu-Natal, suggested that multiple factors might have contributed to the die-offs, as changes in water quality or temperature can make fish more susceptible to disease.
The mass sardine deaths have also led to operational issues. Koeberg Nuclear Power Station, located north of Cape Town, was forced to reduce power output by 50% on one of its two units because dead sardines clogged a seawater intake pipe. This incident affected the only nuclear power station in Africa.