Alarming Mass Sardine Die-Off Poses New Threat to South African Penguins

Seabird researchers and marine scientists are anxiously observing a mass sardine die-off along the Cape coastline due to concerns about its potential ripple effect on the already critically endangered African Penguin population. The die-off is possibly linked to the pilchard herpesvirus pathogen, a virus newly reported in South African waters. This situation draws parallels to similar sardine die-offs in Australia in the 1990s, which led to significant mortalities and reduced breeding success for the Little Penguin population, raising serious concerns for the African Penguin.

Early findings indicate worrying weight loss in African Penguins at three of the seven breeding colonies: Dyer Island, Stony Point (Betty's Bay), and Robben Island, coinciding with the recent sardine mortalities. While researchers caution that it's too early for firm conclusions, data from Dyer Island showed a considerable decline in average bird weight for ten to twelve days, although it has since recovered somewhat. Stony Point also experienced a decline, albeit slightly later, with some birds recording significant weight drops. Robben Island observed a dip, but recovery within a week, indicating mixed results possibly influenced by varying penguin diets, such as anchovies.

The African Penguin, listed as "critically endangered," is intensively monitored at its breeding sites, with current estimates at around 19,800 mature individual birds. Monitoring includes an Automated Penguin Monitoring System using small weighbridges to track bird weight and movement without disturbance. Weight, typically between 2.2-3.5kg, is a critical health indicator. Sardines are particularly vital for African Penguins outside the breeding season, enabling them to maintain good condition, which significantly impacts adult survival and overall population numbers.

The Department of Forestry, Fisheries and the Environment (DFFE) initiated diagnostic testing on August 3, following reports of dead and dying sardines from August 1. By August 14, laboratory investigations confirmed the presence of pilchard herpesvirus genetic material in sampled sardines. However, the DFFE noted that the virus was detected in both dead and, at lower levels, apparently healthy sardines. This suggests that the virus alone might not be sufficient to cause mass mortality, prompting scientists to investigate potential environmental stressors such as harmful algae, low oxygen, or unusual oceanographic conditions as contributing or triggering factors. Preliminary findings have largely ruled out toxins as the primary cause of death.

In response, the DFFE has convened an urgent briefing with the small pelagic fishing industry and is establishing a task team to formulate a coordinated response plan. The routine October/November hydro-acoustic biomass survey will be crucial in assessing the overall impact of the virus episode on the sardine population. The DFFE has assured the public that there is no evidence the virus infects people or other animals, and commercially caught or canned sardines are safe. However, the public is strongly advised not to collect or consume dead or dying fish, nor to feed them to pets.

Regarding the African Penguin population, recent news presents a mixed picture. The Boulders Beach colony in Table Mountain National Park recorded a welcome 13% increase to 790 breeding pairs in June 2026. Small improvements were also noted at Robben Island and Dassen Island. Conversely, numbers at the southern Cape colonies of Stony Point and Dyer Island, as well as Algoa Bay colonies (Bird Island and St Croix), have decreased. Overall, the African Penguin population continues to decline, making it difficult to estimate overall trends despite localized increases.

The Small Pelagic Scientific Working Group is scheduled to meet to discuss the critical link between the virus, sardine mortalities, and the potential impact on African Penguins. This ongoing situation underscores the fragility of marine ecosystems and the urgent need for a cautious, evidence-based approach to conservation and fisheries management to prevent crashes in pelagic fish stocks.