Great white shark encounter SA’s first
IT’S A murder mystery the likes of which South Africa’s leading great white shark experts have never encountered: three carcasses washing ashore one after the other.
Their l ive r s were devoured, but little else was eaten. And the culprits? Pods of orcas on a killing spree in Cape Town’s waters, with a predilection for nutritious organs.
“We’ve never seen anything like this,” said Alison Towner, a great white shark biologist from the Dyer Island Conservation Trust, who helped perfor m the landmark dissections on-site, authorised by the Department of Environmental Affairs, with the Marine Dynamics Group and the White Shark Research Group.
The first shark washed ashore in Gansbaai on May 3. A dissection revealed its liver was gone. The next day, another 3.5m shark washed ashore and, on May 7, a third was spotted in Struisbaai.
“Today’s carcass is a 4.2m male and his injuries seem to match those of the previous two dead specimens,” wrote Towner in her blog.
“It seems likely that orcas are again the cause of death but we’ll confirm after the autopsy.
“Nature can be so cruel and the dexterity these enormous animals are capable of is mind-blowing, almost surgical precision as they remove the squalene rich liver of the white sharks and dump their carcass.”
Dr Alison Kock, a marine biologist working on top predators at Shark Spotters, tweeted. “Mind still blown that a 5m white shark ended up as a snack for an orca(s).”
This week, the DEA said examination of the carcasses showed all three had bite indentations consistent with a killer whale predation.
“Small pods of orcas were spotted in and around Gansbaai and False Bay in the preceding weeks. The fact that only the liver of each of these animals was consumed is a common occurrence in nature, where quality is more important than quantity.”
The DEA said it was a “natural phenomenon” and “should be taken in the context of an anticipated shift that occurs in an ecological system due to seasonal/ temporal incidence differing predator and prey regimes”.
Orcas are common to the region. “The sightings of pods appear to be increasing in South Africa, but this may be an artefact of increases in the number of water users and the extent of access along the coastline.
“Killer whales are apex predators and while we are accustomed to viewing great white sharks as occupying the top of the food-chain in our waters, orcas are more specialised hunters and consider almost anything in the ocean as potential prey.”
Towner said: “We’ve identified and matched each of the three sharks in our database. The fact is from now on this is a grey area and we don’t know how long the sharks will stay away from the area as a result of predation pressure.”