Great white sharks vanished from South Africa's most famous hotspots, and scientists can't agree why. In 1991 South Africa became the first country in the world to protect white sharks by law, and for two decades False Bay, Gansbaai and Mossel Bay were among the most reliable places on Earth to see one. Then the sightings collapsed. In False Bay, observers counted about 1.6 white sharks per hour from 2000 to 2015 and about 0.3 from 2016 to 2020, and one Gansbaai cage-diving boat went from more than six sharks per trip in 2011 to fewer than one in 2018. Marine biologist Andrew Lewin, host of Ocean Decoded and co-host of the Beyond Jaws podcast, walks through the public fight over what happened and shows why that fight is good for the sharks.
In 2015 two orcas known as Port and Starboard arrived in False Bay, and by 2017 white sharks were washing ashore near Gansbaai with their livers removed. A 2022 study led by Alison Towner of the Dyer Island Conservation Trust found that after orca attacks, individual white sharks stayed away from Gansbaai for weeks or months. In 2023 a team led by Heather Bowlby of Fisheries and Oceans Canada pulled together every abundance index available and found a relatively flat regional trend since 1991, with human-shark incidents shifting from the Western Cape toward the Eastern Cape. In March 2024 a group led by Enrico Gennari of the Oceans Research Institute answered in the same journal. They argued that the hotspot declines started before the orcas arrived and pointed to human-caused deaths: an estimated 44 white sharks a year killed in KwaZulu-Natal shark nets and drumlines and as demersal longline bycatch, about 5 to 10 percent of the population. Researchers documented 11 orca predations on white sharks between 2017 and 2025, and 18 of 21 sharks tagged in Mossel Bay since 2019 have gone silent.
Andrew lays out the common ground: the Western Cape hotspots emptied, the orcas played a part, and more than three decades of protection haven't produced a recovery. Then he shows how similar fights cracked other ocean mysteries, from the debate over whaling and North Pacific seal and sea lion declines, to the 2025 identification of Vibrio pectenicida in sea star wasting disease, to the replication work that reshaped research on ocean acidification and fish behaviour. You'll leave with three questions for the next scientific debate you see in the headlines, and two things both sides of this one support: long-term standardized monitoring along the whole South African coast and fewer white sharks dying in nets and on longlines. Join Andrew live on Ocean Decoded Live, Monday to Thursday at 5 PM Eastern, and go deeper with How to Protect the Ocean and Beyond Jaws.
Chapters:
0:00 - Two Orcas, One Viral Clip
2:22 - Stable and Shifting East?
4:56 - What the Headlines Missed
7:31 - Acidification and Fish Behaviour
9:40 - Why Debate Makes Science Better
Takeaways:
South Africa was the first country to protect white sharks by law, in 1991.
White shark sightings at False Bay, Gansbaai and Mossel Bay collapsed in the 2010s. Every side of the debate accepts those numbers.
Two orcas, Port and Starboard, began killing white sharks and taking their livers, and sharks fled the hotspots after attacks.
One research team reads the data as a stable population that moved east.
Another argues the declines started before the orcas and that human-caused deaths, about 44 sharks a year, are high enough to drive a decline.
Orca predation is natural and outside government control. Shark nets and longline fisheries are regulated by the state.
Both teams agree the hotspots emptied, orcas played a part and the population hasn't recovered after more than 30 years of protection.
What's still open: whether the total population is flat or falling, and how large the human share of deaths is.
Public scientific disagreement is how evidence improves. Whaling and sea lions, sea star wasting disease and acidification research all show the pattern.
Next time you see a science fight in the news, look for what both sides agree on, what data would settle it, and what can be done while you wait.
#OceanConservation #MarineBiology #SaveOurOceans #ProtectTheOcean #OceanAwareness #BluePlanet #ConservationMatters #ScienceForChange #SustainableOceans
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