DFFE said approximately 75 sardines have so far been included in the PHV testing programme.
Picture: iStock
The Department of Forestry, Fisheries and the Environment (DFFE) is continuing to investigate the recent sardine mortality event, with early evidence increasingly pointing to pilchard herpesvirus (PHV) as the leading explanation.
No new mass-mortality incidents have been reported since Sunday, 16 August. The department said this suggested the acute phase of the event may have eased, although monitoring and testing remain underway.
PHV testing continues
DFFE said approximately 75 sardines have so far been included in the PHV testing programme.
Initial testing by the South African Institute for Aquatic Biodiversity and Rhodes University detected PHV genetic material in 15 fish.
“Of these, 10 fish collected from the mortality event showed consistently high viral levels,” the department said.
Viral levels varied among five fish that were caught alive and appeared healthy when collected. The viral sequence showed a 99.7% match to an Australian PHV gene.
The department has also processed about 60 additional samples for PHV screening, with preliminary results showing high PHV levels in roughly half.
Confirmatory testing is continuing, while pathological examinations of another 40 samples are underway.
These examinations will determine whether the fish show the characteristic gill inflammation and damage associated with active PHV infection.
Other causes investigated
DFFE said investigations found no evidence that harmful algae were the primary cause of the deaths.
“Paralytic shellfish toxins were not detected, while domoic acid and yessotoxin occurred only at low levels,” it said.
The department also examined stomach contents and material rinsed from the fish’s gills but found no harmful algae at densities likely to have caused the mortality.
Unusually cold water and low-oxygen conditions were recorded along parts of the West Coast. However, DFFE said these conditions were broadly similar to those observed during a recent pelagic recruitment survey, when no dead or dying sardines were found.
Low oxygen also occurs periodically along the West Coast without previously causing sardine deaths on this scale.
“The apparent restriction of the mortality to sardines makes a general environmental cause less likely,” the department said, while cautioning that environmental conditions could still have contributed to the event.
“Taken together, the evidence increasingly points to PHV as the leading explanation,” it said.
PHV poses no known human health risk
DFFE reiterated that PHV is a fish virus and poses no known risk to human health.
“There is no evidence that it can infect or cause disease in people,” the department said.
However, the public has been urged not to collect, consume or feed dead or dying sardines to pets.
Task team agrees on response
A high-level task team involving DFFE, affected municipalities, management authorities, the fishing industry and other stakeholders has held its first meeting.
The group agreed on a coordinated response plan covering expanded surveillance and testing, clearer guidance on disposing of dead fish, public-health communication and an assessment of the possible impact on the sardine resource.
DFFE said it would provide further updates as results are confirmed.
