Rabies in Cape fur seals is now a confirmed and alarming development along the South African coastline. False Bay, home to both Cape fur seals and Cape Research and Diver Development (Cape RADD), has long been a paradise for marine biologists, tourists and locals alike. Snorkelling and diving among the playful and curious Cape fur seals is an iconic local experience that many love—including us at Cape RADD. However, recent developments have dramatically changed this joyful encounter.
What’s behind this startling change? It’s a complex ecological puzzle involving increasing human pressure on the marine environment, harmful algal blooms (HAB’s), and an unprecedented outbreak of rabies in Cape fur seals.
A New Marine Threat: Rabies in Cape Fur Seals
Rabies in Cape fur seals was first detected in 2022 and confirmed in 2024. This is the first time rabies has established itself among marine mammals. It is now endemic in the Cape fur seal population in South Africa.
How Did Rabies Spread to Cape Fur Seals
Genetic analyses indicate the virus originated from terrestrial wildlife. Scientists believe a coastal jackal carrying rabies likely bit a seal, transferring this terrestrial virus into the marine environment. The highly social and densely populated colonies of Cape fur seals allowed the disease to spread rapidly.
Beyond Rabies: The Toxic Algae Connection?
Before rabies was confirmed, marine scientists noted unusual aggression among seals. Initially, this was linked to harmful algal blooms (HAB’s) also known as red tides. While these can be naturally caused, they can be intensified by nutrient pollution, such as agricultural run-off and inadequately treated sewage.
These HAB’s not only harm seals, but many marine animals – including us. Stay informed on current bloom conditions along the coast via the OCIMS Harmful Algal Bloom app.
HAB’s produce domoic acid, a potent neurotoxin that causes neurological symptoms in seals and can harm humans who consume contaminated shellfish. Scientists have suggested that we can use seals as sentinels to monitor the spread of HAB’s.
Aggressive seal encounters: rabies or domoic acid poisoning?
Between 2022 and 2023, aggressive seal encounters at beaches like Clifton and Hout Bay were initially attributed to HAB’s. However, the confirmation of rabies in Cape fur seals complicated the picture. Researchers now suspect that rabies and domoic acid might interact to exacerbate aggressive seal behaviour.
Since 2021, 72 people in South Africa have been attacked by Cape fur seals, including eight confirmed rabies cases—highlighting the growing public health risk.
False Bay Under Stress: Climate and Human Impact on Cape Fur Seals
False Bay’s ecological issues go deeper. Climate-driven changes, including intensified upwelling, enhance algal bloom conditions. Meanwhile, human-induced pressures like boat noise can disrupt seal behaviour and raise stress levels. These factors could reduce resilience and may contribute to disease outbreaks.
In 2021, thousands of Cape fur seals died along South Africa’s West Coast which indicates deeper problems. Government investigations identified malnutrition as the primary cause. However, scientists like Dr Tess Gridley from Sea Search, warned that many seals are chronically ill, pointing to broader ecological stressors still at play.
Therefore, seals aren’t just victims but indicators of broader environmental stresses, reflecting the health of the entire marine ecosystem.
Economic and Tourism Impact of Rabies on Cape Fur Seals
Furthermore, the outbreak of rabies in Cape fur seals has disrupted marine tourism, particularly seal snorkelling tours. This illustrates how ecological crises quickly evolve into economic ones.
How You Can Help
Addressing this crisis requires collective action:
Reduce Nutrient Pollution
- Support improved wastewater treatment, such as by reporting pollution to the City of Cape Town.
- Encourage sustainable farming practices.
- Help at home by gardening responsibly, using eco-friendly products, saving water and avoiding drain dumping.
- For more tips click here.
Support Marine Research
- Participate in citizen science projects
- Help monitor seal populations and environmental conditions
Practice Responsible Wildlife Interaction
- Maintain safe distances from marine wildlife
- Report aggressive or unusual seal behaviours to the local state veterinarian linked in the FAQ’s below
- Consult the frequently asked questions about rabies and for what to do if you are bitten by a seal
Cape RADD’s Role
Cape RADD, based in False Bay, is committed to marine conservation through education and citizen science. Although our current focus isn’t specifically on seals, this crisis offers new opportunities to help monitor and protect marine life.
By joining Cape RADD, you can directly contribute to vital research on the health of False Bay’s ecosystem.
🌊 Join Cape RADD: Snorkel for Science!
Become part of our passionate citizen science community. Help us track marine health, protect False Bay’s extraordinary wildlife, and contribute meaningfully to conservation research.
👉 Participate in One of Our Citizen Science Projects Today!
Together, let’s safeguard Cape Town’s marine ecosystems and the incredible wildlife that calls them home.
📚 Key References
🦭 Rabies in Cape Fur Seals
- Oberhosel, G. (2024, July 31). Rabies outbreak in Cape fur seals: Navigating a new South African reality. Daily Maverick. https://www.dailymaverick.co.za/article/2024-07-31-rabies-outbreak-in-cape-fur-seals-navigating-a-new-south-african-reality/.
- Western Cape Department of Agriculture. (2024). Rabies Awareness FAQ – Seals. Official guidelines and explanation of rabies in marine environments. View PDF
🧪 Harmful Algal Blooms (HABs) and Domoic Acid
- Bryce, E. (2022, May 25). What’s killing South Africa’s seals? Dialogue Earth. https://dialogue.earth/en/uncategorized/whats-killing-south-africas-seals/
- Thomson, J. (2023, January 17). Hyperaggressive seals likely poisoned with acid are attacking humans. Newsweek. https://www.newsweek.com/hyperaggressive-seals-likely-poisoned-acid-are-attacking-humans-1774551
- Ngcuka, O. (2023, January 4). Seal attack at Clifton beach could be linked to toxic algae bloom. Daily Maverick. https://www.dailymaverick.co.za/article/2023-01-04-seal-attack-at-clifton-beach-could-be-linked-to-toxic-algae-bloom/
- Hendrix, A. M., Lefebvre, K. A., Quakenbush, L., Bryan, A., Stimmelmayr, R., Sheffield, G., … & Marcinek, D. J. (2021). Ice seals as sentinels for algal toxin presence in the Pacific Arctic and subarctic marine ecosystems. Marine Mammal Science, 37(3), 1292–1308. https://doi.org/10.1111/mms.12822
- Li, Z., Wang, J., Yue, H., Du, M., Jin, Y., & Fan, J. (2023). Marine toxin domoic acid alters nitrogen cycling in sediments. Nature Communications, 14, 7873. https://doi.org/10.1038/s41467-023-43265-4
- OCIMS (Oceans and Coasts Information Management System).South Africa’s national tool for HAB tracking.
Visit HAB Monitoring App
🌊 False Bay Ecosystem & Human Impact
- Pfaff, M.C., et al. (2019). A synthesis of three decades of socio-ecological change in False Bay. South African Journal of Science.Comprehensive review of pressures on the False Bay ecosystem.
- Martin, R., et al. (2023). Anthropogenic noise impacts on Cape fur seals during breeding season. Reveals how boat traffic and human noise affect seal behavior.
- Department of Forestry, Fisheries and the Environment (DFFE). (2022). Results of investigation of the mass mortalities of seals along the West Coast released. www.dffe.gov.za
- Sea Search for scientific contributions on seal aggression, disease, and environmental stress.
- Gridley, T. in Joseph, S. (2022). Investigation into large-scale Cape fur seal die-off continues. IOL. Link
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