As of late quite a bit of research has been done on white shark behavioural patterns, more specifically white shark predation and deterrents by orcas, which have become a point of interest. The orca (Orcinus orca) has been known to be one of the most intelligent predators on the planet. We’ve learned that recently, thanks to a paper by Alison Towner et al, they’ve decided to spice up their menu. The specials? White shark livers.
Great white shark, via Wikimedia Commons
Battle of the Giants
The author has drone footage that captures interactions between killer whales and white sharks. The jaw-dropping footage reveals a meticulously well-thought-out strategy that orcas employ to hunt the great whites. A first orca dives underneath the shark and darts up bringing it to the surface. The shark is now incapacitated and is no longer a threat. The killer whales engage. One big bite into the pectoral fin area of the shark leaves a pool of blood, freeing up the orca’s target. They are after the nutritious shark liver. Seeing as white sharks are mostly cartilage, the only part worth the effort is the liver, the calorific value of which is enough to last an orca a day.
2 Orcas breaching, via Wallpaper Flare
The author then takes a look at different footage captured by a phone from a helicopter. In this particular interaction between killer whales and a white shark, the shark is observed using a defense technique. The shark circles one of the orcas closely, a similar technique used in turn by seals when being hunted by white sharks. Turtles have also been known in some cases to circle bull sharks to avoid being hunted. This technique, while creative, may however prove ineffective against orcas, given that they usually hunt in packs. The white shark circling one killer whale would subsequently result in it being in the path of another.
Fight or flight
An interesting fluctuation in sightings occurred following these two sightings of interactions between white sharks and orcas. On the one hand, a shark diving company noticed a severe decrease in white sharks in Mossel Bay. Sightings went from up to 5 a day, to none for a considerable amount of days afterwards. One can theorize that the orcas preying on white sharks may have triggered a flight reaction in the population of white sharks in Mossel Bay. On the other hand, a drone flying over the coastline for an average of 59 minutes after the day of the predation quotidianly, noticed a similar phenomenon. The absence of white shark sightings by the drone and the company indicates that orcas may act as a white shark deterrent.
Great white shark, via Flickr by Elias Levy
Although white sharks are often portrayed as man-eating monsters in the media and popular culture, they are vital to our oceans. In reality, white sharks are not the villains many people think they are. You are more likely to die at the hands of a vending machine than by a shark attack. They are apex predators and are essential to the ecosystems they find themselves in. At the top of the food chain, they keep the lower trophic level animals from becoming too abundant. For instance, without white sharks, the amount of fur seals would flourish an unhealthy amount. These seals in turn would eat more fish and further cascading effects may follow.
What are the consequences?
Due to orca predation on white sharks, they may be moving eastward. These raise certain questions about the ecology of the surrounding area questions arise.
For example, will the seal population increase? And if so, what does that mean for the fish population of False Bay? Would this then cause macroinvertebrate diversity to increase since there may be fewer fish? Uncertainty in marine communities and population dynamics means monitoring the ecosystem would be vital. Only time will provide answers to these questions but what remains certain is that we cannot underestimate the importance of sharks in our ocean.
Seal Island in False Bay, via Flickr
To conclude, orca predation is causing the white shark population to migrate. It seems after a white shark hunt occurs in a certain area, the other white sharks are aware and avoid the said area. If orca predation were to get worse and the white shark numbers in our waters were to decrease, it could alter our ecosystems. Nonetheless, the adaptation that orcas adopt time and time again to create new hunting techniques is astounding. More research on these interactions must be done to draw more concrete conclusions.
If you would like to learn about other groundbreaking discoveries happening along the South African coast and take part in monitoring projects for these species, consider joining our Field course or our volunteering course.
Towner, A.V., Kock, A.A., Stopforth, C., Hurwitz, D. and Elwen, S.H., 2023. Direct observation of killer whales preying on white sharks and evidence of a flight response. Ecology, 104(1).