Wildlife

Shark-eating killer whales move into Cape Town

Scuba divers diving along a popular site inside Table Mountain National Park discovered a broadnose sevengill shark graveyard within a protected area known to be home to an exceptionally large group of the sharks.

At any given time, divers in this area typically come across roughly 70 sharks in an hour-long dive, this is the only noted place in the world that is as populated by such a large concentrated number of sevengill sharks.

The cause of the mass deaths remained a mystery at first due to the inability to recover shark bodies for examination, and suspicions fell on great white sharks, humans and killer whales, or orcas.

Months later scientists managed to examine shark carcasses and determined that the culprit was indeed orcas.

After reviewing information on orca behavior, dietary specialisation and population delineation both globally and locally, it was decided these attacks might be due to the arrival of a different sub-group of killer whales that feed specifically on sharks.

At the same time as the dead sharks were first discovered, a local whale-watching charter documented the arrival of two new killer whales in the bay in January 2015. These individuals were easily identifiable by their characteristic bent dorsal fins, and were nicknamed “Port” and “Starboard”. They were sighted near the sevengill aggregation site at the time of both incidents of mass shark deaths in 2015 and 2016.

It is suspected that these same two orcas were also responsible for the deaths of five great white sharks further up the coast in Gansbaai in 2017.