PHV was detected in dead sardines and, at lower levels, in some apparently healthy fish collected along the West Coast
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A virus never before reported in South African sardines has been detected in fish linked to recent mass mortalities along the West Coast, but authorities say its presence alone may not explain the deaths.
Laboratory sequencing confirmed pilchard herpesvirus (PHV) genetic material in sampled sardines, prompting further investigation into whether environmental factors also contributed to the mortality event.
The Department of Forestry, Fisheries and the Environment (DFFE) said on Friday that PHV was detected in dead sardines and, at lower levels, in some apparently healthy fish collected along the West Coast.
Virus may not be sole cause
The department said the findings indicated that the virus alone may not have been sufficient to cause the mass mortality.
“Scientists are therefore also investigating whether an environmental stressor, such as harmful algae, low oxygen or unusual oceanographic conditions, may have triggered or intensified the event. This remains a hypothesis requiring further evidence,” it said.
Investigators also tested sardines collected off Saldanha Bay, the Cape Canyon and Gansbaai for toxins associated with harmful algal blooms.
An apparently healthy comparison sample from St Helena Bay was also tested.
The department said none of the paralytic toxins associated with a harmful algal bloom in Saldanha Bay were detected.
“Two other algal toxins, domoic acid and yessotoxin, were detected at low levels, with the highest levels found in the apparently healthy comparison sample,” it said.
“No other toxins included in the screening were detected.”
The results suggested the toxins tested for were unlikely to have been the primary cause of the sardine deaths, although the department said they did not completely rule out harmful algae or environmental conditions as contributing factors.
Task team to coordinate response
The DFFE has convened an urgent briefing with small pelagic fishing industry stakeholders and will establish a task team involving the department, the fishing industry and other relevant stakeholders.
The team will formulate a coordinated response plan to address PHV-associated sardine mortality in South African waters.
The department said disease surveillance was being expanded along the West, South and East coasts while disease, pathology and environmental investigations continued.
“Through a coordinated inter-agency effort, the department is expanding disease surveillance along the West, South and East coasts,” it said.
The routine hydroacoustic biomass survey scheduled for October and November will provide the first opportunity to assess the possible impact of the mortality event on the sardine population.
The department said PHV had not previously been reported in South African sardines. The virus was associated with two large-scale sardine mortality events in Australasia during the 1990s, but was later detected in apparently healthy Australian sardine populations without causing continuous mortality.
PHV is associated with sardines, also known as pilchards. There is no evidence that it infects people or other animals.
No general fishing suspension
The DFFE said detecting PHV did not mean commercially caught healthy sardines or canned sardine products were unsafe.
“The finding does not currently justify a general suspension of fishing or canning,” it said.
The department added that the biotoxin results were reassuring but did not amount to a general clearance of all commercial catches.
“Monitoring and normal food-safety controls should therefore continue,” it said.
The public was advised not to collect or consume dead or dying fish and not to feed them to pets.
The DFFE said it would provide further information as additional results from the investigation became available.
