White sharks: Secrets of a Top Predator
SHOW NOTES
In all her time studying white sharks, one experience stands out in Alison’s memory [06.08]. She and her colleagues were tracking a large female white shark at night, when something very special happened. “There was no moon, it was very, very dark and we were tracking her as she was swimming through bioluminescence. All you could see was the outline of her shape gliding through the water. This perfect shape outlined in bioluminescence. We were so fortunate to see this, but then after a few minutes there was a huge breach! She breached completely out of the water and there was an explosion of light.” It’s an image that Alison has tried to recreate in the years since. “I tried to get AI to generate an image, but it didn’t really do it justice,” she says.
Alison’s journey to this moment started while she was studying for a degree in marine biology at the University of Cape Town, in quite an unexpected place – a car wash [11.41]. She was working for a car wash at weekends, and would check the cars for valuables prior to driving them into the bay to be washed. One day, while opening the boot of a car, Alison came across a stack of posters that showcased great white sharks jumping completely out of the water. “And I was like, ‘what is this?’” she laughs. “I’ve studied marine biology for three years, and nobody told me about breaching great white sharks?”. Captivated, Alison asked the owner of the car about the posters in his boot. It turned out they belonged to a friend of the car’s owner, who just so happened to be world-renowned shark photographer Chris Fellows. In exchange for a free car wash, Alison was introduced to Chris – an introduction that would lead her into a lifelong career: “That started my journey of working for Chris, and his partner at the time, Rob. And I was a field guide on their boat for two years, from 1998 to 2000.”
Alison’s time as a wildlife guide allowed her to start observing the behaviour of great white sharks in the wild, particularly around False Bay in Cape Town – one of the best places in the world to see white sharks at the time. This population would then become the focus of her research.
But before we learn about Alison’s studies on white sharks, let’s first dive into the animal itself [16.00]. The largest of all the predatory sharks, white sharks can reach up to six metres in size and are decidedly bulky. They have a pure white underside – which is where the name comes from – and light to dark grey on the dorsal side. “And they really just embody the word ‘shark’ in many, many ways,” says Alison. “They really have that quintessential shape of a shark, that torpedo shape…a very classic triangular-shaped head, big dorsal fins.”
White sharks tend to prefer cold, temperate waters, but have a wide-ranging distribution in most of the world’s oceans, including tropical and even estuarine environments [19.32]. “It’s probably easier to say where you don’t find them!” Alison says. The reason for this is that white sharks are one of the few endothermic species of shark, meaning that they can keep their bodies at a higher temperature than that of the surrounding seawater. This allows white sharks to tolerate many different conditions and inhabit a wide variety of ecosystems. “…they really are one of the most wide-ranging species of shark that you get, and they’re highly tolerant of a range of different water temperatures, adaptable to different ecosystems, habitats. And this is what really makes them such a successful predator,” explains Alison.
Alongside endothermy, white sharks have a number of other adaptations that really make them the ultimate predator [29.25]. One is their size and powerful, muscular body, which allows them to hunt and capture large, energy-rich prey. Another is their dentition. Adult white sharks have top teeth that are broad and serrated, like a steak knife, perfectly designed to slice through large prey like seals, dolphins and whales. “The bottom teeth act like the fork and knife, holding the prey in place,” adds Alison. An interesting fact is that a white shark’s teeth change throughout its lifetime as they take advantage of different prey opportunities. Younger sharks have more pointed teeth, made for grasping slippery prey like squid. As they grow and are able to hunt for larger prey, the top teeth broaden. “Collectively, these adaptations really mean they can occupy spaces all the way from the coast through to the pelagic environment and take advantage of prey opportunities that other species, like other big sharks – predatory shark species like bull sharks or tiger sharks – can’t do,” summarises Alison.
Alison’s research has focused primarily on the South African white shark population, namely in the iconic False Bay [31.50]. Located right at the tip of Southern Africa, it is the largest natural bay in Africa and, until recently, was the ideal habitat for great whites. It is influenced by two major ocean currents – the warm and fast-flowing Agulhas current and the cold, slow-moving Benguela current – which results in high biodiversity. “There’s no extremes…the temperature’s quite mild, lots of different species occur there. So, at the foundation of it all, you’ve got really favourable habitats for white sharks all year round,” explains Alison. “You’ve got seasonally abundant prey that’s available all year round, and it’s a relatively sheltered area as well.” There is also Seal Island, which is home to over 70, 000 fur seals – a favourite dining spot of white sharks.
Alison’s early work involved observing the predatory behaviour of white sharks around Seal Island [37.35]. She found that there were very specific times of day, mainly the first two hours of sunrise, where sharks were the most focused on hunting seals and were the most successful. “We believe that this had to do with the low light levels, which gave the sharks advantage over the seals swimming at the surface,” says Alison. During this time, negative interactions between humans and sharks occurred closer inshore, causing Alison to broaden her focus to the wider False Bay area. She expanded her work to tag and track sharks in the inshore coastal areas, and found that many of the tagged animals were spending their time inshore. “And this really busted down many theories about rogue sharks,” recalls Alison. “We were able to use science to very clearly demonstrate that [the negative interactions were] very unlikely a rogue shark scenario, and that the sharks were literally there almost every single day during the summer.” She also found that only female sharks made the move inshore. During the autumn and winter months, both male and female white sharks would visit Seal Island when the Cape fur seal pups were learning how to swim, and therefore easier to catch. Come spring and summer, the males would leave the bay completely, but the females would start to head inshore, where they would remain until the following autumn. These findings led to some interesting headlines in the local newspaper. “I remember seeing one of the best headlines I’ve ever seen…it was “we see she sharks on the seashore!” laughs Alison.
It was important to communicate these findings to the general public before they were published in a scientific journal, as there was a real human safety issue [41.34]. “I think that once people understand a little bit more, once they understand that it’s not one rogue shark swimming around with a taste for blood…that they’re mostly female sharks that are coming inshore and that the females are really important for the future of the population and we know that they play really important roles in how the ecosystem looks and functions…I think it countered this negative narrative around sharks at the time,” says Alison, of sharing her findings more widely. At the time, people were calling for a mass culling of sharks to reduce the risk of shark bite incidents. It was a challenge for a young shark researcher, but Alison’s findings helped foster understanding and awareness around these animals. Then, in 2008, Alison started working with Shark Spotters, a pioneering organisation aiming to foster coexistence between people and sharks. Forethinking surfers and local authorities put forward the idea to hire local car guards and fishermen to stand on the mountainside overlooking False Bay, and monitor the water for sharks. If they spotted a large shark, they would alert the surfers, and people would leave the water. And the programme was very successful. “I then started to collaborate more closely with Shark Spotters as well, and bring the research program into Shark Spotters so that we could use that evidence to inform management, policy, awareness and understanding. So you had this combination of actually doing something that was working, i.e. shark spotters, combined with science and understanding, and then also education and awareness. And that’s kind of the core principles of Shark Spotters. And that is this multi-pronged approach to looking at this challenge between conserving this important top predator, which is also potentially dangerous to people.”
But False Bay is changing [54.19]. The white sharks have all but disappeared, and have gone from a familiar fixture to a rare occurrence. Evidence suggests that there are a few reasons for this, but the primary cause is predation by orca – specifically two individuals that, in the last 10 years, have specialised in predation of large, coastal sharks. What exactly this means for the False Bay ecosystem is difficult to say at present, but it has highlighted the influential role of white sharks. “With [the disappearance of white sharks], we’ve seen quite a few changes and that includes some of [the other] animals becoming much more bold(er)… It’s that fear factor,” explains Alison. “And to kind of give you another example of this, we, in addition to our tagging research, (we) also did aerial surveys along the coast. And when I would see lots of white sharks on the inshore…I saw nothing else. Nothing else. When I did flights when the white sharks weren’t around, I counted stingrays, seals, schools of fish. Now that doesn’t mean that those animals were not there. They’re there, but they’re a lot less bold than when they are with white sharks present.” In short, the removal of such an apex predator has had knock-on effects throughout the whole ecosystem, and the real implications of that is yet to be seen.
These changes aside, white sharks are a species that continues to surprise Alison, even 20 years after her first encounter [60.01]. For example, she has just discovered that one of the white sharks she tagged in False Bay in 2012 was caught and killed in Indonesia. While the fate of this animal is sad, it really demonstrates how far they can travel. “Indonesia is 38 000 kilometres away from where it was tagged…so again, surprising us with one of the longest ocean migrations,” says Alison. She also recalls a time with National Geographic, when they attached cameras onto the dorsal fins of white sharks, allowing Alison to see through the eyes of the species she has studied for so long:
“Seeing what the shark is seeing for those few hours just showed me that they really are so incredibly inquisitive, investigatory, interested in the environment, and they’re certainly not swimming around mindless with, you know, not having an idea of where to go and what to do…They know exactly where they want to go. They’re exploring everything in their way, in their pathway. And it just really speaks to the successfulness of this species of shark, and why it really is the quintessential shark.”
ABOUT OUR GUEST
Dr Alison Kock
Dr Alison Kock is a marine biologist at the Cape Research Centre, South African National Parks (SANParks) and an Honorary Research Associate with the South African Institute for Aquatic Biodiversity and the Institute for Communities and Wildlife in Africa at the University of Cape Town.
Alison’s research interests are broad and include investigating the socio-ecological role of top predators, particularly large, coastal sharks, and evaluating the effectiveness of marine protected areas. She leads research and long-term ecological monitoring in four marine protected areas in the Northern and Western Cape of South Africa under the management of SANParks.
Alison completed her PhD in biological sciences at the University of Cape Town in 2014 during which time she also co-established the Save Our Seas Foundation Shark Centre in Kalk Bay and helped to strategically grow the non-profit organisation, Shark Spotters, whose vision is the sustainable co-existence of people and sharks. She currently serves on their executive committee.
Alison is committed to ensuring that scientific information is effectively translated into management and policy actions and thus also serves on several national scientific working groups including the National Marine Biodiversity Scientific Working Group, the Top Predator Scientific Working Group, the South African Whale Disentanglement Network, the Seabird Technical Team and the Scientific Authority of South Africa.
Follow Alison on Instagram here.
