Famous for a few things, False Bay on the south coast of the Western Cape is a mecca for tourists from around the world. The natural beauty and quaint seaside towns are enough to keep any visitor busy exploring for days. But it is the Marine Big Five that steals the show for most tourists. They arrive by the thousand, pen in hand, to tick these marine animals off their bucket lists.
Marine Big Five
For those of you who don’t know, the Marine Big Five are the Great white shark, Southern right whale, dolphin, Cape fur seal and the diminutive African penguin. It is possible to see these creatures from the land, from a boat in the sea, underwater in a cage, in a kayak (for the lucky ones) or from beaches like Boulders in Simons Town.
It is commonly accepted that the Great white shark is the top dog apex predator in these waters and Gansbaai has become a mecca for shark cage diving. Recently however the carcasses of White sharks have been washing up on the beaches of the Western Cape and what makes these findings super interesting is the surgical precision with which the animal’s livers have been removed.
Hunting the Hunter
What’s big enough to eat a 4.9 meter long White shark? In May this year, three carcases were washed ashore in the space of a week. A fourth carcass was confirmed by Marine Dynamics and the Dyer Island Conservation Trust on the 24th of July. That is a 4.9 meter female, 3.4 meter male, 4.5 meter male and lastly a 4.2 meter male. These are mature animals and for an endangered species this loss of life is tragic.
After conducting necropsies (or animal autopsies), the Marine Dynamics researchers concluded that all four sharks had suffered the same injuries “a large gaping hole between pectoral fins where they were torn apart to reveal the body cavity … and that their large livers were completely missing”. Marine biologist Alison Towner said at the time “We have never seen anything like this”. She concluded that in light of the similarity of injuries and the recent sightings of orcas in the area that it “provides convincing evidence that the orcas are responsible for the shark’s death”.
Orcas, Killer Whales … The Wolves of the Sea
Orcas are the true apex predators of the ocean meaning that they themselves have no predators. These marine mammals (Orcinus orca) are the largest member of the dolphin family and average around 8meters in length. They are known to have complex social structures and amongst pods even develop dialects.
Orcas are known for their intelligence and are therefore adept and adaptable hunters. They are above sharks on the oceanic food chain and as a result their prey can be just about anything from seals and dolphins to dugongs and turtles. Due to their social habits and the fact that they hunt together, they are also known as the Wolves of the Sea.
Sightings of Killer Whales in False Bay in Cape Town are rare but not unheard of. In early 2015, David Hurwitz of the Simons Town Boat Company was called out on an Orca spotting expedition and was lucky enough to see a pod of over 20 individuals. David says that Common dolphins seem to be their meal of choice and this is what he was expecting. Although he has sent hundreds of hours on the water interacting with marine animals he says that there is just “something extraordinary about Killer Whales”.
Port and Star Board
Hunting in pairs, Killer whales have been observed flushing sharks to the surface before splitting them open and alowing the liver to float to the surface where it is consumed. Unlike other fish which have swim bladders to control buoyancy, sharks use their liver which accounts for almost a third of its body weight!
The killings are being attributed to a pair of orcas called Port and Starboard due to the slanting of their dorsal fins. It is not known why these two are frequenting South African waters but it seems that the nutrient rich livers of the White sharks are just too good to resist.
The Bad and the Good
The Great white predation is unprecedented and Marine biologists and scientists just don’t have anything to compare it to.
The down side is that the appearance of a white shark carcass seems to correlate with a no-show of white sharks. Winter, usually the best time to see White sharks, has been very quiet. Both species, White sharks and Killer whales are transient, meaning that they migrate between areas and this could mean only a temporary interuption. Towner says that the worrying thing is that they just don’t know what will happen next.
On the bright side, who fancies an addition to their bucket list? The Marine Big Five + 1. Sightings of Orcas in South Africa, in general, are on the rise and this too could be an opportunity for some of the best land based orca sightings anywhere in the world!
Bring on the Marine Big Six – White shark, Dolphin, Southern right whale, Cape fur seal, African Penguin and The wolf of the Sea - the Killer whale.