The magnificent Great White shark (image from National Geographic)
Think of the Great White Shark, and you may hear the ominous tones of the famous John Williams score from the iconic 70’s movie Jaws, but there is so much more to Great Whites than the monster of Amity Beach.
Sharks are ancient, appearing in the fossil record before trees even existed and lasting through multiple mass extinction events! As long ago as 450 million years, shark like scales have been found in the fossil record, although teeth have been recorded from this time, suggesting early sharks were toothless. 410 million years ago, shark teeth turned up in the fossil record, followed shortly by the species Antarctilamna, which looked more like eels than sharks, but possessed the teeth we recognise today. When the carboniferous period arrived 369 million years ago, so did the golden age of sharks. Just prior to the arrival of this era, a global mass extinction event wiped put 75% of life on earth, leaving space in the ecosystem for sharks to dominate. During this time, some truly crazy looking sharks evolved, like the Stethacanthus with a huge anvil shaped dorsal fine, the Helicocoprion with a spiral buzz saw bottom jaw and the species Falcatus, the males of which had long spines protruding out of their backs. At the end of the Permian period 252 million years ago another mass extinction event wiped out 96% of all life, including most of the marine life, leaving just a few species of shark clinging to existence.
The bizarre looking helicoprion with it buzz-saw jaw! (image from https://www.sci.news)
In the Early Jurassic period around 195 million years ago, the genus Hexanchiformes or the sixgill sharks evolved along with other more modern shark species with more developed jaws and faster swimming. The earths fifth mass extinction arrived in the Cretaceous period, affecting even the sharks this time. Only the deepest water and smallest species survived the asteroid strike and took quite some time to evolve into larger species, eventually developing as big as the famous megalodon, the largest shark to have ever lived, hitting lengths as big as 18 metres.
Comparing the size of modern to prehistoric sharks (image from www.santacruzsentinel.com)
For a long time, scientists believed the great white shark was closely related to the megalodon with their morphological similarities (aside from the obvious size difference!), but the recent discovery of a new fossil species, dubbed the Caracharodon hubbelli, showed intermediate features between present day white sharks and prehistoric makos. Great whites were initially placed next to the Megalodon as their teeth were very similar, but the discovery of this very well preserved fossil of this intermediate species revealed that the closest relatives of Great Whites are actually the mako sharks.
The fossilized jaws of an ancient species of Great White. The discovery of this fossil enabled scientists to better plot the tree of shark evolution (image from www.floridamuseum.ufl.edu)
Great White Shark: Great Physiology
Great Whites are perfectly designed for life as a marine apex predator. Found in almost all coastal and offshore waters with temperatures between 12 and 24 degrees Celsius, Great Whites are concentrated particularly around the coasts of California and the Northeastern United States, South African and Japan. They are classed as epipelagic fish, living predominantly in the depths of water where light penetrates, although they have been recorded diving much deeper, as deep as 1200 metres, for periods of time. They congregate anywhere there is sufficient prey for them, including fur seal and sea lion colonies, cetaceans, other sharks and shoals of large, bony fish. Although they are predominantly seen feeding on the surface, these deep dives, reaching areas where the bioluminescent fish swim, could possibly be hunting trips. Some scientists hypothesize they might be feasting on squid down there, and there is more speculation that these deep dives might become more necessary with climate change affecting food webs in the ocean.
Although they are well known as coastal predators, tagging studies have revealed that sharks travel to an area between the Baja Peninsula and Hawaii, called the White Shark Café, and spend as long as 100 days there. They certainly aren’t heading there in droves to pick up an iced latte, so what exactly are they doing congregating in this specific area? They have been recorded reaching depths as deep as 900 metres, but no one knows exactly what they are doing; it could be some kind of social interactions with other sharks, or seasonal feeding or mating. More research is needed before we can say with any confidence why the White Shark Café is so important.
The paths taken by tagged Great Whites, showing the popular area between California and Hawaii, dubbed the white shark cafe (image from Whitesharkcafe.com)
Like orcas, great whites have countershading, with darker blue-grey colouration on the top, and white bellies. This means they can blend into the dark ocean when seen from above and can blend into the bright sunlight when seen from below. The mottling pattern on their side breaks up the silhouette of the shark. Aside from the basking shark and the whale shark, the Great White is the largest shark species, and there are some reports of truly legendary sharks that have been allegedly caught in the past, with some unconfirmed historical reports listing sharks as large as 11 metres! One of the largest sharks that has been confirmed is Deep Blue, a female shark that was spotted by shark researcher Hoyos Padilla and his team as they tracked hunting sharks of the coast of Gaudalupe Island. She is estimated to be over 50 years old and is 6.1 metres long and weighs 2.5 tons!
The beautiful Deep Blue, the largest Great White Shark recorded currently (image from www.surfertoday.com)
Sharks have several amazing adaptations that make them the super-efficient predators that they are. All sharks have specialised electroreceptors in their noses called the Ampullae of Lorenzini, which can detect electromagnetic fields that are emitted by moving animals. Great Whites can pick up on variations as small as one half of a billionth of a volt and can even detect immobile animals from their heartbeat. Great Whites can also maintain their body temperature exceptionally well in an example of a phenomenon called gigantothermy, where large animals can more easily maintain a constant hight body temperature due to their smaller surface area to volume ratio. They also have the rete mirabile (Latin for wonderful net), a web like structure of veins and arteries that we have seen in other animals, especially those living with extreme temperatures. This blood vessel structure conserves heat by warming cooler arterial blood with venous blood warmed by working muscles. This keeps their body temperature higher than the surrounding water, allowing them to hunt their fast, agile prey.
There is a reason why Great White prey especially on seals and sea lions. With their thick layer of blubber, these animals provide the Great Whites with a high fat meal. The sharks will pack this fat into their livers and use the high fatty content of their livers to sustain them on their long travels across the nutrient poor ocean to the White Shark Café.
Unlike many apex predators, great whites don’t seem affected by the accumulation of toxins in the marine food chain. Studies of blood samples drawn from white sharks in South Africa found lead, arsenic and mercury at levels that would be fatal to other marine apex predators, and yet the sharks were healthy, and their blood showed good levels of white blood cells. Sharks are known to be excellent at healing and avoiding age related ailments, and scientists are still studying their physiology to understand why they have such super immune systems.
Of Jaws and Judgement: the lethal legacy of the movies
One of the most famous and well-respected movies features the Great White, the 1975 Steven Spielberg thriller, Jaws. Sadly, this movie and the book it is based on, written by Peter Benchley, sealed the image of the Great White in the public’s mind as the savage man eater that terrorized the idyllic seaside town of Amity. Generations were left too frightened to enter the water, images of the bloody attacks from the movie fresh in their minds, in a public that at the time had had very little exposure to sharks. A study in Australia found that the ‘Jaws effect’ was at least partially behind the introduction of a controversial shark culling bill in Australia, as the general perception was that sharks were just killing machines that were deliberately hunting humans.
The poster for the famous and well loved movie Jaws, featuring a monstrous Great White as a villain (image from IMDb)
Unfortunately, it is a fact that most recorded bites are Great Whites, but most of them are test bites, when the shark is testing what the unusual creature in the water could be. After all, it’s not like they have hands to reach out and check! The sheer size of Great Whites and the power of their jaws, with an estimated 1.8 tonnes of bite force, can make these test bites fatal for the unfortunate individual involved, with fatalities often caused by severe blood loss. It was often hypothesised that sharks attacked humans, particularly surfers, as they mistook them for seals when silhouetted on the surface of the water. There has been some controversy over this, with other scientists suggesting that sharks can differentiate, but are attacking either over territorialism or curiosity over the humans in the water. However, a study using model seals and mounted cameras moving at the same speed as a hunting shark revealed that there is some likelihood that sharks could easily see a human as a seal and attack. Ultimately, sharks do not want to eat humans; we DO NOT taste good to them and are far too bony and not fatty enough for sharks that nee fat to travel huge distances. And the statistics remain that there are more deaths from cows annually than sharks and the chance of dying in a shark attack in the United States is as low as 1 in 3 billion. Between 2011 and 2017, 259 people died from taking selfies, in contrast to 50 shark related deaths! Perhaps we should be more careful of the phones in our pockets than the shark cruising past the beach.
Despite this, the terrifying legacy of jaws remained for years. Both Peter Benchley and Steven Spielberg have expressed deep regret for the distorted view of sharks Jaws created. Ultimately, we must remember as the audience that Jaws is a horror movie with a villain, no different to Freddy Krueger in the Nightmare on Elm Street and just as fantastical. Peter Benchley explained that the shark could have been anything but was merely a tool to explore how different people react to disasters. It could just have easily been a tsunami or a serial killer in place of the shark. Up until his death, Peter Benchley worked as a marine conservationist, championing marine protected areas and working to change attitudes towards sharks. He received many positive letters over the years, with people expressing how Jaws inspired them to learn more about sharks by becoming marine biologists. Although Jaws is undoubtedly his most famous work, he wrote another book called ‘The Girl of the Sea of Cortez’ about a young island girl who encounters a huge, benign manta ray, who she protects from ocean exploitation. He now even has a marine conservation award named in his honour.
Peter Benchley, author of Jaws, who became a dedicated marine and shark conservationist (image from www.peterbenchley.com)
Who is the real threat?
Ultimately, we must realise that although shark attacks do occur and are frightening and often bloody, they are rare. What is not rare however is the killing of sharks by humans; 100 million a year, in shark culls, as accidental bycatch in the fishing industry or the brutal slaying of sharks for their fins for shark fin soup. Shark culling, often referred to by the more benign term shark control, is the deployment of drumlines and nets around beaches to catch sharks swimming near the shoreline. If sharks are found alive on the drumline, they will be shot. Many of the sharks killed, particularly in the harsh culling schemes in Australia and Kwa Zulu Natal in South Africa are white sharks. These drumlines are rarely species specific and often kill turtles, fish and dolphins, massively harming the marine ecosystem. These harsh measures are not even shown to reduce shark attacks! A study of the 2014 shark cull in Australia revealed there was no correlation between this cull and a reduction in shark bite incidents.
The cruel reality of shark drum lines, which kill hundred to thousands of sharks and other marine animals each year (image from outdoorsqueensland.com.au)
Of relevance to white sharks, there is much discussion ongoing surrounding the popular practice of cage diving. It still remains a pretty controversial topic; on the one hand it brings education and money, but on the other there are concerns that it may increase harmful shark-human interactions, teaching great whites to associate humans with food. Especially in cases where the boat operators will chum the water or use decoys and hung baits to attract Great Whites, shark scientists worry this will increase shark attacks, although there is no direct evidence yet that this is the case. White sharks can also be deliberately hunted as trophies due to their size, which is particularly concerning as they are so essential as the top of the food chain.
Conservation optimism
Currently, Great Whites are listed as vulnerable on the IUCN red list, and charities like the WWF have implemented extensive research and monitoring programmes in the last few years to better understand how shark populations are faring against shark culls and changing oceans. The Shark Trust, a UK based charity, has three main goals for shark conservation; species protection through legislation, fisheries management to reduce bycatch and responsible trade to reduce the demand for non-sustainable shark products like shark fins through their stop shark finning campaign. You can learn about this campaign and more at Great White Sharks | Species | WWF (worldwildlife.org).
Stricter controls need to be brought in to reduce over-fishing and preventing shark by catch and the use of better fishing techniques that more accurately target commercial fish species and not vulnerable sharks and rays.
Sharks are well protected in American waters, but there is still a lot of ongoing controversy in Australia and South Africa over shark culling measures. Thankfully though, attitudes towards sharks are beginning to change. Often people are more fascinated than frightened. Even after shark attacks, often heavily sensationalised in the media, there is less of a public backlash than has been previously expected. People understand the importance of sharks in our oceans and protest harsh ‘control’ measures like shark culling.
Ocearch is another not for profit that facilitates research and the tagging of sharks around the world. All their research is conducted aboard the MV OCEARCH, which is an at sea laboratory with a specialised hydraulic platform to lift mature marine animals out of the ocean for tagging and study. They also have a tracker app that you can use to track sharks right from your phone! Check this out and more at About – Ocearch. You can see shark research in action right from your phone!
Awesome videos!
References
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MASSIVE THANK YOU TO RACHAEL DA SILVA FROM THE UK FOR THIS WRITE UP! PLEASE FOLLOW HER ON INSTAGRAM AND HER WILDLIFE ARTWORK AT TILLY_MINT08
