Cape Town – No dead or dying sardines have been reported to the Department of Forestry, Fisheries and the Environment since Thursday, 6 August, suggesting that the recent mortality event along the Western Cape coast has run its course.
West Coast canneries continue to accept healthy sardines caught north of St Helena Bay, while some factories in affected areas have elected to await the department’s results before resuming operations.
The cause has not yet been confirmed.
A wide-ranging investigation involving the department, research institutions, specialist laboratories, the fishing industry and other collaborating scientists is continuing.
Samples of dead sardines have been obtained from Saldanha Bay, Hout Bay, Betty’s Bay, Gansbaai and the Cape Canyon area.
Apparently healthy sardines from Elands Bay and Lambert’s Bay have also been collected for comparison.
South African Institute for Aquatic Biodiversity (SAIAB) and Rhodes University are undertaking disease testing, while SAIAB and a specialist commercial laboratory are screening samples for marine biotoxins.
The department’s scientists are examining water samples, stomach contents and gills for evidence of harmful algae.
Basic biological examinations, including measurements of size, weight, condition and maturity, and macroscopic examination of the gills, have also been undertaken.
A harmful algal bloom caused by Alexandrium catenella was present in Saldanha Bay when the mortality began.
This harmful alga has previously been associated with sardine mortalities in South Africa and remains one of the possible causes under investigation.
However, it has not been detected in the water samples or sardine stomach contents examined to date, and preliminary analyses have not identified a harmful-algal cause.
Oceanographic information supplied by SAEON and the CSIR indicates enhanced upwelling, unusually cold nearshore water and low oxygen in St Helena Bay before the event.
A southward-moving coastal current could also have transported affected fish from the West Coast towards Cape Point and farther east.
These observations provide useful context but do not establish the cause.
No wider effects on the marine ecosystem have been reported to date.
Sardines are nevertheless an important food source for seabirds, seals and predatory fish, and the department will continue to monitor any possible effects on the sardine population and its predators.
As a precaution, while testing continues, members of the public should not collect or consume dead fish found on beaches.
The department thanks the fishing industry, individual fishers and vessel crews, CapMarine, BirdLife South Africa, SAIAB, Rhodes University, SAEON, the CSIR, Cape Nature, other collaborating scientists and specialist laboratories, and members of the public who supplied reports, photographs, videos and samples.
The response demonstrates the strong links between government, research institutions, specialist laboratories and the fishing industry, enabling multiple parallel lines of investigation to proceed rapidly.
The department said further updates will be provided once disease testing and initial biotoxin results are available, most likely early next week.
These specialised analyses take time because samples must undergo several stages of preparation, testing and verification before the results can be interpreted reliably.
