Pilchard herpesvirus detected in West Coast sardine deaths

The department has called an urgent briefing with stakeholders in the small pelagic fishing industry and plans to establish a task team involving government, industry representatives and other relevant parties.

Scientists investigating recent sardine deaths along South Africa's West Coast have detected genetic material from pilchard herpesvirus in samples, although authorities say more evidence is needed before the virus can be identified as the sole cause of the mortality event.

The Department of Forestry, Fisheries and the Environment (DFFE) said on Friday that laboratory sequencing confirmed pilchard herpesvirus, known as PHV, in dead sardines and at lower levels in some fish that appeared healthy when collected. The discovery has widened the investigation rather than providing a final explanation, as the presence of PHV in apparently healthy fish suggests that infection alone may not necessarily result in large numbers of sardines dying.

Scientists investigate environmental stress

Researchers are examining whether environmental conditions could have weakened the sardines or intensified the effects of the virus, with harmful algae, low oxygen levels and unusual oceanographic conditions among the possible factors under investigation.

Testing has already provided some clues. Sardines collected near Saldanha Bay, the Cape Canyon and Gansbaai, together with an apparently healthy comparison sample from St Helena Bay, were tested for toxins linked to harmful algal blooms.

No paralytic toxins associated with a harmful algal bloom in Saldanha Bay were found. Two other algal toxins, domoic acid and yessotoxin, were detected at low levels, with the highest concentrations appearing in the apparently healthy comparison sample.

According to the DFFE, the results make it unlikely that the toxins included in the screening were the primary cause of the deaths, although scientists have not ruled out harmful algae or other environmental conditions that could have placed additional stress on the fish.

Task team to coordinate response

The department has called an urgent briefing with stakeholders in the small pelagic fishing industry and plans to establish a task team involving government, industry representatives and other relevant parties.

Its immediate responsibility will be to develop a coordinated response to PHV-associated sardine mortality in South African waters while scientists continue disease, pathology and environmental investigations.

Surveillance is also being expanded along the West, South and East coasts through an inter-agency effort, giving researchers a broader picture of whether the virus or unusual sardine mortality is appearing elsewhere.

The department's routine October and November hydroacoustic biomass survey is expected to provide the first opportunity to assess what effect, if any, the mortality event has had on South Africa's wider sardine population.

Virus has history of sardine mortality overseas

PHV has not previously been reported in South African sardines, making its detection particularly important for fisheries scientists and authorities monitoring the health of local stocks.

The virus was associated with two major sardine mortality events in Australasia during the 1990s, although it was later detected among apparently healthy Australian sardines without causing continuous deaths.

PHV is associated with sardines, which are also commonly known as pilchards, and authorities say there is no evidence that the virus infects humans or other animals.

Its detection in healthy fish is one reason researchers are continuing to examine whether a combination of disease and environmental stress may better explain what happened along the West Coast.

Fishing and canning continue under normal controls

The DFFE said there is currently no justification for a general suspension of sardine fishing or canning, stressing that detecting PHV does not mean healthy commercially caught sardines or canned products are unsafe. Biotoxin test results have also provided some reassurance, although the department cautioned that these findings should not be regarded as a blanket food-safety clearance for every commercial catch.

Normal monitoring and food-safety controls will remain in place while investigations continue, allowing authorities to respond if further laboratory or environmental evidence changes the current assessment. Members of the public have been advised not to collect or eat sardines found dead or dying along the coastline and not to feed affected fish to pets. The DFFE said further updates will be provided as additional test results become available and scientists gain a clearer understanding of the factors behind the unusual sardine deaths.