Whether it caused by is how different their bodies are to ours or the fact that they live in such remote, alien worlds, there is a pervasive misconception that sharks are unintelligent killing-machines; reacting viciously to any stimulus in their environment and not capable of any type of sophisticated thoughts. This belief is so ingrained that I am very commonly asked why it is that I like sharks so much... many people are afraid of sharks, they do not understand them, they believe they are mindless, soulless, man-eaters, that are out to get us. They are the horror movie villain, the scourge, the monster... assumed to be cold and heartless. But this is simply not true. Over recent decades, research into shark neurobiology has come on leaps and bounds, and we now know that - far from being 'mindless killing machines' - sharks are much more cognitively advanced than we ever imagined...
Only Human
One of the reasons why people fear sharks is because of the terrible human habit of "anthropomorphising" - that is to say, projecting our human traits onto animals. We might imagine that our dog is smiling when he looks up at us or think a cat is being spiteful by continuously peeing on the floor, for example. Whilst it is very possible that many creatures are intelligent, sentient and potentially even capable of emotion in some form, it is foolish to attribute human traits to other animals because they have evolved under a completely different set of circ*mstances to us and therefore, their senses, behaviours and cognition are adapted to a completely different world (Darwin, 1872; Wynne & Udell, 2020).
When it comes to sharks, our anthropomorphising has lead to us assume that sharks have some malign, malicious intent when they attack humans (as a person would), rather than simply presuming they must be hungry and that they have confused us with something good to eat. This has lead to the comical, yet disturbingly pervasive idea of the vengeful, man-eating 'rogue shark' that was made famous in the movie Jaws (to learn more about this issue, head over to The Jaws Effect).
This is completely inaccurate. In reality, sharks do not initiate assaults on humans out of spite or some need for revenge, and they do not hold a grudge. Those are human traits!
Size Matters
Whatsmore, as sharks are nothing like a cute, engaging dog or a soulful-eyed tiger, people often think they are simple, unintelligent or vacant. Yet this could not be further from the truth.
As a general rule, animals with a relatively larger brain are more cognitively advanced. This does not mean that larger-bodied animals, like elephants, are necessarily smartest, as it is actually the size of the brain in relation to the size of the body that matters. So animals with a large brain-body ratio are usually the most intelligent (excepting birds). This is known as the "encephalisation" (Jerison, 2002; Brown & Schuessel, 2023).
When we measure sharks up against other types of animals using this method, it's obvious that they have very large brains compared to their bodies. So sharks may be more similar to dogs and cats - in terms of their level of mental acuity - than they are to other fishes. They even have a larger encephalisation quotient than many reptiles and even some birds (Jerison, 2002; Brown & Schuessel, 2023).
Thinking It Through
These big brains means that sharks are very intelligent. In fact, far from being mindless, sharks are known to be as cognitively advanced as mammals or birds, and they are capable of many highly evolved tasks. Sharks can learn to solve mazes, be trained to do basic arithmetic, use tools, recognise visual cues and follow internal "mental maps" for navigation, and form long-standing, stable relationships with "conspecifics" (other sharks of the same species) that are akin to friendships (Schluessel, 2015; Brown & Schuessel, 2023). To learn more check out Jaws and Brains.
Sharks need this broad suite of cognitive skills because they are predators living in dynamic, complex environments. So, over millions of years of evolution, they have developed enough brain power to be able to continuously monitor, assess and respond to their environments, so that they can solve problems, avoid predators, track down prey and mates, and navigate through their habitats (Schluessel, 2015; Brown & Schuessel, 2023).
Picky Eaters
So we have debunked the absurd idea that sharks are 'mindless', but are they 'killing machines'? Well there is no doubt that sharks are magnificently well-adapted predators, yet the indication that they thoughtlessly consume anything and everything that they come across in their environment is simply ludicrous. There are some species that are "generalists" and eat quite a broad range of prey, but many species of sharks have quite strict dietary preferences and are actually very picky about what they eat. In fact, in several species, sharks have been observed spitting out low value prey in favour of saving space for a better quality meal (Compagno, 1984).
As an example, dusky smoothhounds (Mustelus canis) are "specialists", whose feeding behaviours, jaws and teeth morphology make them perfectly adapted for catching and crushing the skulls of crabs. They are not exactly the fearsome beasts of monster movies (Gerry, 2008).
The classic movie villain, the white shark (Carcharodon carcharias) is a generalist with a broad diet (including squid, octopi, fishes, other sharks and marine mammals), but even they are selective in what they eat. Scientists have proven that great whites behave very differently around different types of baits. High quality food items elicit predatory attacks from the sharks (such as "horizontal strikes" and vertical "breaches" to take the bait at the surface of the water), but lower value items or those that are frozen, are treated more with curiosity. Instead of eliciting feeding responses, the sharks "mouth" at these foods to investigate them until they discern they were not palatable and they leave (Becerril‑García et al, 2020).
It's Lonely at the Top
Additionally, only a small handful of the 540 plus species of sharks that we know about today are "apex predators" - most are much lower in the "food chain". In fact, the majority of shark species, in fact, are less than a metre in length when fully grown and fall prey to many other, larger predators. They are simply too small to even be capable of swimming around killing everything in their way (Compagno, 1984). See Myth Busted: NOT ALL Sharks Are Apex Predators! for more information.
At the other end of the spectrum, some of the biggest sharks species - whale Sharks (Rhincodon typus), the basking shark (Cetorhinus maximus) and megamouths (Megachasma pelagios) - are filter-feeders. Swimming about sedately and living on only microscopic "zooplankton", you could hardly call these animals 'killing machines' (Compagno, 1984).
I'm Full
Finally, the term 'killing machine' is just absurd because sharks simply do not kill for the heck of it (it's humans that do that!). Sharks only kill to eat, when they are hungry. Full stop. End of.
On average, sharks require 2 - 3% of their body weight in food per day, but this statistic varies between species. For instance, the sedate, slow-growing Greenland shark (Somniosus microcephalus) consumes less than 0.2 kg of food daily, but a typical 1,000 kg white shark needs to eat over 18 kg of prey a day in order to fuel their active lifestyle. Yet, no species of shark will eat when they are not hungry and they will stop eating when they reach their limits. They are not insatiable machines with an endless lust for flesh (Compagno, 1984).
In fact, as sharks generally eat less consistently than humans do - some going days or even months between meals - and they are incapable of getting fat, one could say that the term 'eating machine' might better describe human beings than it does sharks.
References
Becerril‑GarcíaEE, Hoyos‑Padilla EM, Micarelli P, Galván‑Magaña F & Sperone E (2020). Behavioural responses of white sharks to specific baits during cage diving ecotourism. Scientific Reports, 10:1. Access online.
BrownC & SchluesselV (2023). Smart sharks: a review of chondrichthyan cognition. Animal Cognition,26:1. Access online.
Compagno LJV (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. FAO Species Catlogue: Rome. Access online.
DarwinC (1872). The expression of the emotions in man and animals. In: Porter DM & Graham PW (Eds.).The Portable Darwin. Penguin Publishing Group: UK, pp. 364–393.
Gerry SP (2008). Feeding Mechanics of a Trophic Generalist and a Specialist Shark Species: A comparison of Diet, Behavior and Function. University of Rhode Island Dissertation. Access online.
Jerison HJ (2002). Evolution of the Brain. In: Encyclopedia of the Human Brain. Access online.
RoffG, Doropoulos C, Rogers A, Bozec Y-M, Krueck NC, Aurellado E, Priest M, Birrell C & Mumby PJ (2016). The ecological role of sharks on coral reefs. Trends in Ecology and Evolution, 31:5. Access online.
SchluesselV (2015). Who would have thought that ‘Jaws’ also has brains? Cognitive functions in elasmobranchs. Animal Cognition, 18. Access online.
Wynne CDL & Udell MAR (2020). Animal Cognition; Evolution, Behaviour & Cognition. Bloomsbury Academic Press: UK.
By Sophie A Mayco*ckfor SharkSpeak
