What Is Responsible for the Harvesting of Great White Sharks' Livers?

Even those who haven’t seen Jaws are able to recognize the theme tune and will almost certainly know that it’s a movie about a deadly great white shark, also known by their scientific name Carcharodon carcharias. Great white sharks are recognized as being at the top of the natural food chain: they’re apex predators, and as such are usually the ones doing the killing. However, in recent years, the carcasses of several great white sharks have been washing up on the shores of the Western Cape in South Africa. Interestingly, the carcasses were all found to have their livers missing; their bodies had not been completely savaged but the liver had been tactically removed and harvested by another predator. It has been proven and is now known that orcas, also called killer whales, are responsible for this harvesting. It appears that a battle has commenced between two of the sea's greatest apex predators, and at the minute orcas seem to be winning the fight.

One of the big questions is: why would the orcas target the livers of these sharks?

Bony fish, known as teleosts, possess an organ known as a swim bladder. They fill this bladder up with gas that then provides them with enough buoyancy to stay floating at a particular level of the ocean, and they move up and down with the release or input of gas. Sharks are elasmobranchs and do not possess a swim bladder, so their liver has taken up this important function. The livers of great white sharks are rich in fat, protein, carbohydrates and vitamins and are reported to have more energy in them than whale blubber. It would, therefore, be very beneficial for orcas to consume shark livers, considering their high metabolism.

How are orcas able to attack one of the greatest predators of the sea?

Orcas, unlike great white sharks, hunt in groups and recent reports have noted that orcas may be using a trait of elasmobranchs known as tonic immobility in order to paralyze their vulnerable prey. Tonic immobility is a state of paralysis which occurs when you place an elasmobranch, such as a great white shark, on its back in the water. Great whites cannot pass water over their gills unless they are swimming. This means that if they are placed belly side up for too long, they won’t be able to gain enough oxygen to survive. Orcas are said to use this natural paralysis to reduce the exertion that is needed when pursuing and eating the livers of these sharks.

What does this mean for the tourism industry?

Areas such as Gansbaai are known to be hotspots on the South African coast for Great white shark activity. In fact, in previous years there have been guaranteed sightings of great white sharks on any trip taken to the area. However, with the increase in predation of great white sharks by the orcas, there has been a noticeable decrease in these sightings. If the sharks smell that another shark has recently been predated in the area then they will avoid it for a considerable amount of time. If orcas continue to predate in the area, great white sharks could become a rare sight.

I recently went on a university field trip and went on a trip that operated from the Gansbaai region in order to see some sharks. Indeed, in the past ten years that the trip has been running, bar one year, they have never failed to see great whites. However, this year there was no sign of them and I experienced first-hand the changing dynamics of the region and its tourism. Instead, we saw copper-head sharks that have only recently been coming up to feed at the boats. This new phenomenon of orcas harvesting Great white sharks' organs is a potential threat to Cape Town’s shark diving industry but ultimately is a natural phenomenon which really there is nothing we can do about.