Un virus mortel menace les sardines d'Afrique du Sud

A deadly virus has been identified in sardine populations along South Africa’s coastal regions, triggering widespread concern among scientists, environmental groups, and fisheries officials. The outbreak began with the appearance of thousands of dead sardines washing up on beaches in Gqeberha, with similar incidents reported earlier in the Western Cape. Local authorities and researchers suspect the presence of pilchard herpesvirus (PHV), a pathogen previously responsible for massive sardine die-offs in Australia and New Zealand during the 1990s. The phenomenon was first observed last week when large numbers of deceased sardines and pilchards were found along the shores of Gqeberha, particularly on Hobie and Pollock beaches. Environmental organizations described the scene as distressing, with residents expressing alarm over the sudden and extensive fish deaths. Scientists from Nelson Mandela University, including Professor Nadine Strydom, noted that the visible impact on shorelines represented only a small portion of the total mortality, as many affected fish likely remained submerged beneath the surface. This follows a similar mass die-off reported weeks earlier along the Western Cape coast, raising questions about a possible regional spread of the virus. The Department of Forestry, Fisheries and the Environment (DFFE) stated that a connection between the recent occurrences in Gqeberha and the Western Cape is likely, though further verification is needed. PHV has been confirmed in South African waters since July, following tests on sardines collected from areas such as Saldanha Bay, Cape Canyon, Elands Bay, and Gansbaai. Genetic analysis revealed a high degree of similarity, over 99 percent, to the strain responsible for outbreaks in Australia. According to Strydom, this marks the first documented occurrence of PHV in South African waters. Despite these findings, the DFFE emphasized that the presence of the virus does not definitively establish it as the cause of the fish deaths. Officials are investigating whether the virus is acting independently or exacerbating pre-existing conditions in the sardine population. Factors such as low oxygen levels in seawater and harmful algal blooms could weaken fish immune systems, making them more susceptible to infection. Testing conducted by the government found no signs of paralytic shellfish toxins, indicating that algal poisoning is not the main factor behind the die-offs. The situation has taken a critical turn with reports of sardine strandings extending into Namibia, signaling a potential broader ecological crisis. In addition to affecting commercial fisheries, the outbreak has disrupted operations at the Koeberg nuclear power plant near Cape Town, where dead sardines blocked water intakes, forcing the electricity provider to reduce output at one of its units. Conservationists warn of far-reaching consequences for marine ecosystems, as sardines serve as a vital food source for species such as dolphins, seals, seabirds, and the critically endangered African penguin. Environmental experts caution that the long-term effects of the virus remain uncertain. Craig Smith, a senior technical specialist at WWF South Africa, highlighted the severity of the situation, noting that in Australia, PHV led to the collapse of 70 percent of the sardine stock. He expressed concern that South Africa could face a similar fate, potentially followed by a more severe second wave of infections. In Algoa Bay, which hosts one of the world's largest African penguin colonies, the loss of sardines threatens to compound existing challenges related to food scarcity for these birds. As investigations continue, scientists and conservationists are collaborating with government agencies and industry stakeholders to monitor the situation and develop responses. The focus remains on understanding the full scope of the outbreak, assessing its impact on marine biodiversity, and implementing measures to mitigate future risks. Researchers are urging continued vigilance, emphasizing that the current crisis underscores the delicate balance within oceanic ecosystems and the need for sustained monitoring of aquatic health.