The existence of sharks in the ocean dates back more than 400 million years, making them older than many well-known dinosaurs. They are a success story of evolution, as they are uniquely adapted to their ocean habitat, with six highly refined senses – smell, hearing, touch, taste, sight and electromagnetism. The king of all the sharks, the Great White Shark (Carcharodon carcharias), is the apex predator in the ocean, with great intelligence and a body designed for hunting.
Built to hunt
The shape of the great white shark – similar to that of a torpedo – allows it to swim up to 35 miles (50 kilometers) per hour. It has seven rows of teeth, with approximately 300 teeth in total. These sharks also have a well-developed and large brain that coordinates with highly-developed senses. The favorite prey of the sharks include seals and dolphins, which are very clever animals, and sharks have enough brains to outsmart them. Despite their famous reputation as lone hunters, sharks have been observed cooperating with other sharks, hunting in groups and sharing the prey.
Great white sharks became the top predators in the ocean through the evolution of highly-sensitive senses and physiology. The most acute sense used by great white sharks is their smell. They are able to smell a single drop of blood in 10 billion drops of water. Their nostrils are located on the underside of their snouts and lead to an organ called the olfactory bulb. The olfactory bulb of great white sharks is the largest of any shark species.
Sharks also have internal ears, which may be small, but are extremely powerful. These ears can sense vibrations in surrounding water, allowing them to detect prey. Despite their life underwater, these sharks also have great vision. Their retinas are divided into two sections – one adapts for bright light, and another for low-light conditions.
Apart from the same five senses that humans have – smell, taste, touch, hearing and sight – sharks have an additional sense that humans are amazed at. Sharks have electro-reception, meaning they can sense an electrical field. Small pores on the snout of the shark are filled with cells known as the Ampullae of Lorenzini. These cells can feel the power and direction of electrical currents and are used for navigation through the open ocean by using the Earth’s magnetic fields.
Despite their portrayal as ferocious hunters and apex predators, there is a sea creature that has in recent years started competing with great white sharks for these prestigious titles. Orcas (Orcinus orca), also known as killer whales, are known hunters in the oceans, working together as a group to hunt large prey such as whale calves. However, is it possible we underestimated these large cetaceans?
In 2017, two Orcas, affectionately known as Port and Starboard, were spotted along the south-west coast of South Africa. Orca sightings had been reported in these waters for many years before Port and Starboard came along, and were never of any concern. However, in 2017, their presence became significant. These male orcas were recognized by their collapsed dorsal fins – something only seen in 1% of wild orcas – leading researchers to suspect these orcas were possibly highly stressed due to being rejected from their pod.
The south-west coast of South Africa is well-known for the presence of great white sharks, and is a famous tourism destination for people wishing to go shark cage diving. In February 2017, a 2.7-meter female shark washed up fully intact on the beach. Fully intact, apart from a large hole where her liver was supposed to be. At this time, there was still little information available about the presence of the two orcas, so no connection was made, and scientists were baffled by the death of the female shark. In April 2017, another great white shark measuring 4.9 meters, who was tagged and known as “Khaleesi”, was found in the same condition. In May, three more sharks washed up in similar conditions, all with the livers missing. Between each of these attacks, no great white sharks were spotted, making observers wonder if the sharks have fled the waters along the coast. After the third shark was spotted in May 2017, no other sharks were seen for 45 days. At this point, sharks began to return, however Port and Starboard were still present. More sharks continued to wash up, and one thing was evident in all the sharks – they had their liver removed.
It became accepted that the deaths were linked to Port and Starboard, however, the method of attack was still uncertain. A commonly accepted theory is that the orcas stalk the shark from below, ambush the shark, and flips it over. When the shark is belly up, it enters a trance-like state of immobility and starts to drown. The orcas can then take the liver out in a single bite. Due to the liver being rich in nutritional oils, it is the only food the orcas required to survive.
With the absence of great white sharks in the region, another shark species, the bronze whaler shark (Carcharhinus brachyurus) was spotted regularly. Prior to the presence of the orcas, this shark species was very rarely spotted in the area. It appears that the removal of great whites allowed an ecological niche to open up, allowing bronze whale sharks to thrive, making it harder for great whites to return into the same niche.
The great white shark population along the south-west coast of South Africa did not fully reestablish until June 2018, and the presence of Port and Starboard continues to pose a threat to the local population of sharks. It does however appear that 2017 was the worst of it for the sharks.
Other threats to sharks
Despite being apex predators, great white sharks are threatened by another mammal species: humans. Shark nets that are installed along beaches to protect swimmers are entangling sharks, suffocating and killing them, as well as other marine animals such as rays, turtles, dolphins, and whales. Unfortunately, great white sharks can also be victims of accidental by-catch in commercial fisheries that use entangling nets.
The cumulative impacts of multiple stressors, such as contamination, bycatch, coastal development, ocean pollution and climate change are putting great white sharks at risk of extinction. The establishment of connected marine protected areas and regulating fisheries (both commercial and illegal) will greatly benefit the protection of these majestic ocean hunters.