Fear at the top
Scientific publicationTwo Orcas began predating on white sharks at Gansbaai in 2017. This raised questions about their impact on the species presence. This paper aimed to answer some of those questions.
Fear at the Top: Scientific Publication Hello orcas, goodbye great whites
Invited by friend, colleague and shark scientist Oliver Jewell, I was attending the CATs white shark research expedition in Gansbaai, back in 2017.
A week or so before my arrival, a pair of Orcas named Port and Starboard made their presence known in the area. Shortly after, white shark carcasses started washing up on the local beaches with their livers removed – a telltale sign of orca predation.
The white shark population promptly disappeared – I mean almost literally. Before then, I’d never been to the seas surrounding Gansbaai and suffered a missed trip (ie: a trip where you don’t see a great white shark) once. I think we managed to tag maybe three over the following month and no shows became commonplace.
To put this into perspective – Gansbaai has long been considered the great white shark capital of the world, and with good reason. It’s where great white shark cage diving was born, supporting nine local operators on the back of the thousands of tourists who visit every year, specifically to see these animals.
These two orcas aren’t the only thing effecting the great white shark population, but its apparent depletion and their arrival are starkly coordinated.
Alison Towner, lead marine biologist at the Dyer Island Conservation Trust led this research project which also called on the talents of numerous white shark scientists in South Africa.
I created some figures for the project, assisted with data collection and also provided the promotional artwork.
More information: Results and related projects
I strongly encourage you to please read the full publication if you’re interested in more information. To summarise the results, our data suggests that great white sharks not only respond very quickly to the presence of top predators in their ecosystem, but that such scenarios are increasing.
What has been especially interesting to observe, is the response of other wildlife in the area. Almost as soon as the great white sharks moved out, bronze whaler sharks moved in. The species does reside in the area, but spotting them from the tour boat went from being an absolute rarity to a daily occurence.
If you’re interested in other great white shark projects I’ve been involved with in Gansbaai, please do check any of the following pages: