Great white sharks vanish from Gansbaai

In Gansbaai, South Africa, a location once famous for its frequent sightings of great white sharks, the population of these predators has largely disappeared. Scientists point to the actions of two male orcas, known as Port and Starboard, who have been attacking great white sharks since 2017 by removing their livers.

Orcas target great white sharks

The orcas, identifiable by their drooping dorsal fins, have been systematically attacking great white sharks, removing their livers, which are rich in fats. This behavior has led to a significant decline in the local great white shark population, with multiple shark carcasses found in the area showing similar injuries.

Ecosystem changes follow shark decline

The disappearance of great white sharks has triggered a trophic cascade in False Bay. This ecological phenomenon has favored fur seals and seven-gill sharks, which now thrive at the expense of small fish and other smaller sharks in the region.

Shark control program may have worsened the situation

The lethal fishing program of the KwaZulu-Natal Sharks Board is mentioned as a possible factor that may have exacerbated the decline of shark populations along the South African coast. This program involves the use of nets and drum lines to capture or kill sharks.

Gansbaai was once a prime shark site

Gansbaai, once known as the world capital of the great white shark, was a popular site for cage diving experiences due to its frequent encounters with these sharks. The area had a seal colony and nutrient-rich waters that attracted a full marine food chain.

Orcas expand their range

Port and Starboard were first observed near Lüderitz, Namibia, in 2009. After 2015, they began to frequent Gansbaai and other coastal areas, including Port Elizabeth, Cape Town, and False Bay. Their presence coincided with a series of shark deaths, with multiple carcasses found with characteristic wounds.

Research confirms orca attacks

A study published in the African Journal of Marine Science in 2022 identified eight great white shark carcasses since 2017, all showing similar injuries. The wounds matched the method of attack used by Port and Starboard, confirming their role in the decline.

Orcas act alone in new attack

A 2024 study in the African Journal of Marine Science documented Starboard acting alone to kill a juvenile great white shark in under two minutes. Researchers combined data from multiple areas to confirm that the historical population of Gansbaai has indeed left the site.

False Bay experiences similar collapse

A 2025 study by the University of Miami, published in Frontiers in Marine Science, found that False Bay has also experienced a similar collapse in its great white shark population. The study used long-term tracking data to trace the decline and disappearance of sharks in the area.

Trophic cascade disrupts food chain

With the absence of great white sharks, which are a key predator, the Cape fur seals and seven-gill sharks have increased in numbers. These species now feed more heavily on small fish and smaller sharks, leading to a decline in their populations.

Shark control program adds pressure

Researchers remain cautious about the exact causes of the shark decline in False Bay but note that the lethal shark control program by the KwaZulu-Natal Sharks Board is a known factor. This program, combined with the threat from orcas, has created significant pressure on the great white shark population.

Orcas' impact is disproportionate

The story of Gansbaai highlights how a small number of predators, like the orcas Port and Starboard, can have a massive impact on an ecosystem. Their actions have led to the near disappearance of a once-thriving shark population, demonstrating how delicate the balance of nature can be.