Whale Strike Risk Quadruples Off South Africa as Cape of Good Hope Rerouting Brings Surge in Vessel Traffic

A new risk assessment has linked a sharp increase in whale strikes off the South African coast to the rerouting of global maritime traffic around the Cape of Good Hope, following Houthi rebel attacks on Red Sea shipping from 2023 and the subsequent blockade of the Strait of Hormuz. Between December 2023 and December 2024, the number of large vessels travelling through South African waters at average speeds above 15 knots quadrupled according to satellite data, creating a growing collision risk for six baleen whale species whose habitats significantly overlap with the new shipping lanes.

 

Scale and Immediacy of the Problem

 

The collision risk has become tangible in direct and visible ways. In April 2026, two Bryde's whales washed up dead on Dyer Island off the Western Cape coast within a single month, both with shattered vertebrae and propeller marks consistent with vessel strikes. Loraine Shuttleworth, head of research at the Dyer Island Conservation Trust, has described the injuries as unambiguous evidence of ship strikes. The two strandings in a single month represent an unusually high incidence, and researchers and conservationists have stressed that documented strandings represent only a small fraction of total whale mortality, with the vast majority of ship strike deaths going undetected and unrecorded.

 

Scientific Framework and IWC Presentation

 

Els Vermeulen of the University of Pretoria's Mammal Research Institute Whale Unit led the risk assessment, combining vessel tracking data from Global Fishing Watch with species distribution models across six baleen whale species including Bryde's whales, humpback whales, southern right whales, fin whales, blue whales, and sperm whales. The resulting spatial overlap analysis was presented to the International Whaling Commission at its science commission meeting in Slovenia in late April 2026. Vermeulen has emphasised that the precise number of strikes does not need to be known to conclude that increased vessel presence in whale habitat constitutes an elevated risk, and that the data are already sufficient to justify mitigation action.

 

Speed as the Most Critical Risk Factor

 

Vermeulen has identified vessel speed as the most immediate and addressable risk factor, and has called for speed restrictions comparable to the 10-knot limit in force along the US East Coast for North Atlantic right whale protection. The faster a vessel travels, the more likely that a collision will be fatal for the whale, both because of the force of impact and because the acoustic physics of large vessels mean that whales cannot reliably detect approaching ships. Hull design creates a masking effect in which engine noise propagates from the stern while the most dangerous part of the vessel, the bow, can be hundreds of metres ahead and acoustically invisible to a whale surfacing in its path. Ship crews are also typically unaware of collisions, compounding the difficulty of detection and response.

 

Mortality Data and Cryptic Whale Deaths

 

A collation of 50 years of stranding data by Vermeulen's team found that fewer than one percent of recorded strandings were officially attributed to ship strikes, a figure that dramatically underestimates the true scale of collision mortality due to cryptic deaths in which carcasses are never detected or formally recorded. Most ship-related whale deaths occur offshore and the carcasses sink, drift, or decompose before reaching shore. The strandings that do reach the coast are often found by members of the public who may not know to report them to conservation organisations. The significant undercount in official records means that policy responses calibrated to reported mortality may substantially underestimate the true impact of increased shipping on whale populations.

 

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Population Recovery Compounding Risk

 

The problem is intensified by the recovery of some whale populations after decades of protection from commercial whaling. Humpback whale numbers have increased in South African waters since the global whaling moratorium was introduced 40 years ago, and during the Southern Hemisphere spring, particularly between October and November, supergroups of between 20 and hundreds of humpback whales gather to feed in the highly productive Benguela Upwelling System off the southwestern coast of Africa. An increase in vessels traversing whale habitat that overlaps with supergroup aggregations raises the prospect of single collision events affecting multiple animals simultaneously, which would represent a disproportionate impact on locally significant whale concentrations. Species that have not yet recovered, including fin whales and blue whales occurring farther offshore, remain especially vulnerable to any increase in strike mortality.

 

Pathway to Voluntary Guidelines

 

Vermeulen is working with the South African government and other stakeholders to develop national guidelines for shipping companies based on international best practices, including those developed by the IMO and adapted for South African species and conditions. South Africa's Department of Forestry, Fisheries and the Environment has confirmed that discussions are taking place, and the department's spokesperson indicated that ship strikes were raised at the IWC science commission meeting. Vermeulen has noted that many shipping companies appear willing to comply with voluntary measures and that the goal is to develop guidelines that companies can realistically adhere to, beginning implementation now while scientific understanding of offshore whale distributions continues to improve. Alternative shipping routes modelled by the study suggest that risk could be reduced by between 20 and 50 percent without substantially increasing travel distances, though incomplete data on offshore whale distributions currently prevent the recommendation of specific routes.

 

Implications for the Intersection of Shipping and Marine Biodiversity

 

The South African case illustrates how geopolitical disruptions to global trade routes can generate unexpected and serious consequences for marine biodiversity in regions far removed from the original conflict zones. The rerouting of commercial shipping around the Cape of Good Hope was driven by security considerations in the Red Sea and Persian Gulf, yet it has produced a measurable ecological impact in South African coastal waters. This dynamic highlights the need for maritime route planning processes to incorporate biodiversity and marine mammal distribution data alongside the commercial, logistical, and security factors that currently dominate route selection decisions. For the shipping industry, the willingness of companies to engage with voluntary guidelines provides an opening for rapid near-term progress on speed reductions, while the longer-term development of route-based mitigation awaits the completion of more systematic whale distribution surveys.

 

Outlook for Mitigation and Policy Development

 

Speed restrictions represent the most immediately actionable mitigation measure and could be implemented through voluntary guidelines without requiring legislative or regulatory change. Stationing marine mammal observers on vessels operating in high-risk areas has also been identified as a recognised international measure that shipping companies can adopt. The development of formal route-based mitigation will depend on the completion of systematic surveys to map the distribution of offshore whale species whose ranges are currently poorly characterised. The South African government's supportive posture and ongoing engagement with the IWC and IMO frameworks provides a pathway for the translation of scientific findings into operational guidelines, and the urgency signalled by the Dyer Island strandings is likely to accelerate the timeline for voluntary measures even as more comprehensive regulatory frameworks are developed.