CAPE TOWN, Sept. 13 (Xinhua) -- South Africa's environment department said Sunday that a herpesvirus was the most likely cause of widespread sardine mortality spanning 2,600 km of coastline, as investigations into the event continue.
In a statement, the Department of Forestry, Fisheries and the Environment (DFFE) said laboratory testing had confirmed pilchard herpesvirus (PHV) in affected sardines from both the Western Cape and the Gqeberha area, supporting a link between the mortality events.
The deaths were first reported in the Western Cape in late July and later extended eastward along the coast. Similar strandings have been reported in Namibia, although laboratory comparisons are still needed to determine whether they are linked.
The department said the reported locations span about 2,600 km, but mortality was not recorded continuously along the entire stretch. It has received no further reports of dead or dying sardines since Sept. 3, and no strandings have been reported along the KwaZulu-Natal coast.
"Taken together, the consistent detection of high levels of PHV in affected sardines, its confirmation in Western and Eastern Cape samples, and the observed mortality pattern indicate that PHV is the most likely primary cause," the DFFE said.
Investigations have not supported harmful algae or the marine biotoxins screened for as the primary cause, although oceanographic and other environmental conditions cannot yet be excluded as contributing stressors.
"The event cannot yet be regarded as concluded," the department said.
The scale of the mortality remains uncertain. Preliminary estimates depend on assumptions about fish density, the extent of affected coastal areas and the degree to which local observations can be extrapolated.
The DFFE's Small Pelagic Scientific Working Group found no evidence that the mortality had reduced the sardine population enough to warrant a complete closure of the fishery, but recommended a temporary precautionary limitation on catches.
The department said there was also no evidence showing when or how PHV reached South African waters, and no basis for attributing its origin to any particular country, company or product.
A hydroacoustic survey scheduled for October and November is expected to provide the first post-event estimate of sardine biomass and distribution.
PHV is not known to infect people, but the DFFE advised the public not to collect, eat, feed to animals or use as bait dead or dying sardines found near the shore.
It also said the mortality event does not provide a basis for discontinuing commercially produced canned sardines processed under regulatory oversight. ■
