The Hunt
From above the tiger shark’s grey silhouette stands stark against the sun-drenched sands of the sea-floor below. With flowing, almost lethargic, strokes of its tail the shark cruises slowly through the water. As it drifts past a sea turtle, its behaviour suddenly shifts. This time the shark doesn’t continue on its way, as it has done during previous turtle encounters, rather its attention locks in on the reptile.
Directed by senses which have evolved over millions of years for this exact situation, the shark effortlessly closes the distance to the now-alarmed turtle. As the shark hones in on its prey, both animals show a breathtaking display of agility and ingenuity during the ensuing battle. Early on in the encounter, the juvenile tiger shark manages to latch onto one of the turtle’s pectoral (front) flippers in what seems to be a swift end to the affair. Unbelievably, the sea turtle breaks free from the shark’s toothy grip and makes a dash for the safety of the shallow reef – at one point even swimming upside down over its pursuer to keep its shell between vital organs and foe. Although its first potential victim escapes, the shark is undeterred and quickly hones in on another turtle. Once again, the predator grabs a pectoral flipper, yet again the turtle slips free and manages to escape.
This encounter “is not like anything I’ve ever seen”, says drone operator and cinematographer, Carlos Gauna, in the voiceover to his footage posted on his YouTube channel ‘The Malibu Artist’. These are strong words from someone who spends much of his time capturing mesmerising (and often thrilling) drone footage of great white sharks off the coast of southern California.
Gauna, who is “constantly on the search for places that are not necessarily well-known as shark hotspots”, was drawn to the Fernando de Noronha archipelago when he learned about a series of shark attacks which occurred in Sueste Bay, where this footage was captured. Gauna retells that he was immediately stunned by the number of sharks he observed during his first flight over the island. He saw ten lemon sharks hunting anchovies just off the beach. “My first thought was, ‘this is amazing, I wish I could have this water clarity in Southern California’” he told me over email.
The Islands
Rising steeply from the deep ocean floor, an immense undersea volcano dominates the underwater world about 350 kilometres off the coast of Brazil. Four thousand metres above its base, the summit just barely breaks the water’s surface, forming the emerald-green Fernando de Noronha islands embraced by the cobalt backdrop of the southern Atlantic Ocean. Flora and fauna have congregated in this tropical refuge over the 1.5 million years since its formation. As a result, the archipelago boasts a near pristine measure of biodiversity. In fact, 70% of the island’s area is a protected national park and UNESCO World Heritage site.
The tiger shark population of the islands is globally unique. It boasts the highest genetic diversity of any known tiger shark population, and a recently published study suggests that sharks from far and wide congregate in these nutrient-rich waters to reproduce. Dr Bianca Rangel, an author of this study, tells me that the Fernando de Noronha archipelago “is the only area in the Southern Atlantic Ocean proven to play this role in the life cycle of tiger sharks”.
A New Hypothesis
The region, particularly Sueste Bay, may play another important function in the life cycle of tiger sharks – one which is only coming to light through the unique insights drone-based data collection offers. After observing the behaviour of sharks in the bay during his visit, Gauna suspected that juvenile tiger sharks may be using the bay’s shallow waters as ‘practice grounds’ to develop turtle-hunting techniques. His footage and insights prompted Rangel and Fabio Borges – drone documentarian and president of the NGO ‘Instituto Vida na Oceano – to begin utilising daily drone flights as part of their project ‘Tubarões e Raias de Noronha’. Borges tells me that their preliminary observations may support the hypothesis that juvenile sharks are using the area to practice hunting. The researchers almost exclusively see juvenile tiger sharks operating in the bay and although they have recorded dozens of predation attempts on turtles, none have been successful.
Hunting and eating a turtle is no easy feat. The hard, keratin-coated shells of sea turtles are specifically designed to protect the soft internal tissue from attacks by predators. Although tiger sharks are often called ‘generalist’ predators – they’ll indulge themselves on a wide variety of food (and non-food items such as metal, tires, etc.) – they are, in fact, the only extant shark species which has evolved a specialised ‘tool-kit’ to hunt turtles. Their jaws are reinforced with calcium and fused at the centre, allowing the sharks to withstand the immense pressures of biting through turtle shells. These same jaws are lined with strong, heavily serrated teeth, and are able to extend out from the tiger shark’s skull to latch onto difficult-to-grab turtles. Once the sharks have secured their prey, they oscillate their jaws in a unique back and forth motion, effectively ‘sawing’ through the turtle’s shell.
Elsewhere in the world, a recent video captured by Ruth Gaw off the coast of Western Australia shows a tiger shark almost beaching itself in an attempt to catch a turtle.
These adaptations are a result of ‘co-evolution’ between tiger sharks and turtles which has taken place over hundreds of millions of years. A primordial back-and-forth between predator and prey has equipped each with weapons, defences, and strategies that offer an edge over the other. Interestingly for turtles, the asset which most influences their likelihood of surviving a bump-in with a tiger shark is not necessarily any physical defence – like the strength of their shell – but rather, it's their ability to outmanoeuvre the speedy shark. As we see in the video, once the turtle breaks free from the shark’s grasp on its flipper, it displays remarkable agility in dodging the tiger shark’s attacks. From spinning in tiny circles to swimming upside down right above the shark’s head at one point, the turtle manages to keep its shell between itself and the predator before eventually out-swimming the shark to safety.
One can understand why, after watching this impressive display of manoeuvrability from this seemingly ‘lethargic’ sea reptile, more experienced adult tiger sharks may choose a different tactic when hunting turtles. Rather, according to a previous study, the ambush predators generally surprise the marine reptiles from below, incapacitating the turtle before it is able to mount an escape.
Borges explains that before any conclusions can be drawn about habitat usage or differences in hunting techniques between juvenile and adult tiger sharks, more research is needed. He is, however, optimistic, claiming that using drones to capture shark data “is pioneering in Fernando de Noronha, and the preliminary results are very encouraging.”
A new era for research
Clearly, collaborations between videographers like Gauna, scientists like Rangel, and conservationists like Borges can provide the creative impetus to utilise new technologies in innovative ways to the benefit of all. Borges summarises this nexus quite well, “Just as the drone opened up an entirely new approach in generating images for documentaries a few years ago, we realise that there are many new possibilities to be explored in scientific research. The drone allows for new perspectives, both literally and figuratively.”
Top header image: Barry Skinstad
Sharks
Predator vs Prey
Sharks
