South Africa sardine die-off raises virus fears

Thousands of dead sardines have washed onto beaches around Gqeberha on South Africa's south coast, raising concern that pilchard herpesvirus may be spreading through the country's waters.

The Department of Forestry, Fisheries and the Environment said on Sunday that a link between the Gqeberha wash-up and a recent Western Cape die-off was considered likely, but still needed confirmation. It said pilchard herpesvirus remained the leading explanation for the Western Cape mortality event, while other causes and environmental factors were also being investigated.

The department said the virus was first confirmed in South African waters in July after sardines collected off Saldanha Bay, Cape Canyon, Elands Bay and Gansbaai tested positive. Genetic sequencing showed more than 99% similarity to the strain associated with a 1990s Australian outbreak.

Zolile Nqayi, a department spokesperson, said the presence of viral genetic material did not prove that the virus caused the deaths. Scientists are examining whether the virus is the primary cause or is infecting fish already weakened by environmental stress. Government testing found no evidence of paralytic shellfish toxins and only low levels of other marine toxins.

Nadine Strydom, a zoology professor at Nelson Mandela University, said most of the fish found on the beaches were sardines and pilchards, and that the number seen ashore may be only part of the mortality because some fish could be on the seabed.

The investigation is widening after sardine strandings were reported along Namibia's coastline. The department said pilchard herpesvirus poses no known risk to human health.

The die-off has already affected infrastructure. At Koeberg nuclear power station near Cape Town, dead sardines clogged a cooling-water intake basin, forcing the national electricity utility to halve power output at one of its two units.

Scientists and conservation groups warned that lower sardine numbers could affect predators including dolphins, seals, seabirds and the critically endangered African penguin. An intergovernmental task team is coordinating surveillance, testing, disposal of dead fish and assessments of the impact on sardine stocks.