The South African fishing industry and flagship ocean species like penguins are facing heavy weather with all signs pointing to pilchard herpesvirus as the cause of the mass mortality of sardines along the coast.
The appearance of the disease for the first time in stocks of South African sardines, or pilchards as they are also called, likely came from the importation of contaminated South American pilchard in 2020/2021.
And now the mass die-off of such an important prey fish will place great pressure on the marine ecosystem, and the government will need to reduce catch quotas to allow predators especially to weather the storm.
That is the analysis from Nelson Mandela University fish expert Prof Nadine Strydom, who said on Monday she had received several reports showing the mass die-offs were continuing to spread.
“I have received reports of dead pilchards being found 50km east of KuGompo City so the problem, which is almost certainly PHV [pilchard herpesvirus], is moving up the coast in a wave similar to what occurred in Australia in the late 1990s.
“It’s very worrying.”
PHV inflames the gills of the sardine, causing lesions and blocking its oxygen intake, resulting in suffocation.
The August 27 mass wash-up on Gqeberha beaches of tens of thousands of the little fish followed on three weeks of some of the iciest conditions in Algoa Bay for many years.
Open water swimmers, accustomed to swimming through winter temperatures as low as 14°C had to regularly deal with “ice-cream head” and water as low as 11-12°C at times.
Strydom said this was almost certainly not the trigger for the die-offs, however, and it was much more likely the PHV that the fisheries department had already noted as the likely reason for the similar scenario which played out in the Western Cape the previous week.
“Sardines are a cold-water species. If temperature was at all a possibility then we would have seen a number of other species affected, but we haven’t.”
The Makhanda-based SA Institute for Aquatic Biodiversity has shown that the strain of PHV sampled from the fish collected after the recent South African die-offs is almost identical to that confirmed in the 1990s in Australian sardines.
The finding is worrying because in 1995 and again in 1998/1999, Australia experienced some of the most severe mass-mortality events ever recorded in wild fish populations when PHV inadvertently introduced from South America wiped out about 60%-75% of its adult pilchard stock.
Strydom said it was not impossible the South American disease had entered SA waters in ballast water related to increased local shipping due to the Iran War and the closure of the Strait of Hormuz.
“However, it is much more likely that it came in with the frozen pilchard imports that were brought into SA to compensate for our lower stock yields and suppressed fishing activities during the initial Covid period.”
She said the only way forward now was to allow the disease to run its course.
“It’s a new and serious situation for SA to face — this is the first time this has happened and we can only rely on what happened in Australia to guide us on what to expect here in terms of the knock-on effects up the food chain and the repercussions for the fishing industry.
“Given that reality, there’s no way we can fish at our previous quotas, and I’m sure DFFE [department of fisheries, forestry and environment] scientists will be adjusting total allowable catch in the pelagic fishery down accordingly.”
She said her further concern in the meantime was that some fishermen were collecting the dead sardines and freezing them for bait.
“I’m seeing on social media that some guys are doing this.
“But by doing so, you will be preserving the PHV pathogen and releasing it into the water in the months to come to re-contaminate wild populations.
“This is especially problematic with ski boats that fish near shoals of wild pilchard.”
Meanwhile, the national fisheries and environment department said it was probing the widespread die-off of sardines in Gqeberha.
The department said there was a likely link with the Western Cape die-offs, but it would consider all possibilities.
Any early findings that emerge will likely be tabled this week at the scheduled meeting of experts who will consider the effect of the mass die-offs on the sardine population and the fishing industry.
Fisheries spokesperson Zolile Nqayi said the sardine mass mortality incidents in the Western Cape had come to an apparent halt by August 16.
“Since then, isolated sightings have been reported at Bakoven [in Cape Town] and off Tsitsikamma, followed on August 27 by widespread reports of sardines washing ashore around Gqeberha and floating offshore and in the harbour.
“The DFFE is investigating these new reports.”
Nqayi said sardine strandings had also been reported along the Namibian coast, and authorities there had agreed to provide samples for PHV testing.
He said separately, live and dead sardines had been reported in the Koeberg cooling-water intake basin, with seals feeding on them.
Eskom was managing this.
Fisheries had not had access to the site but had obtained a sardine sample for testing.
“PHV remains the leading explanation for the Western Cape mortality event.
“A link with the Gqeberha event is considered likely, but requires confirmation, and other causes and environmental contributions will also be investigated.
“Samples are being collected for further testing, and observers will document the distribution of affected fish and attempt systematic counts at sea.”
He said an intergovernment task team had met on August 26 to discuss the issue.
Responsibilities were assigned and a plan covering surveillance, testing, disposal of dead fish, public communication and assessment of stock impact was developed.
“The DFFE recognises the concerns raised by conservation organisations.
“The Small Pelagic Scientific Working Group will meet on September 4 to review the latest findings and consider their implications.
“This assessment will inform advice on whether additional management measures are warranted.
“The scale of mortality remains uncertain, and the October/November hydro-acoustic survey will provide essential information on the post-event sardine stock status.”
He said as per the August 27 joint statement released by the DFFE and the National Regulator for Compulsory Specifications, “there is no basis to discontinue consumption of commercially produced canned sardines processed under NRCS oversight”.
“These products must be distinguished from dead or dying sardines found on beaches or floating at sea.
“The public should not collect or eat these fish, or feed them to pets.
“PHV is not known to infect people.”
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