Mindless... Souless... Primitive... Killing machines... are all words that have regularly been used to describe sharks in the past. But on the contrary, we now know that sharks have very well developed brains and are capable of many more advanced cognitive functions than we ever realised. If fact, they may be on par with many other vertebrates, like birds. Sharks are intelligent and inquisitive creatures, with a broad repertoire of capabilities and complex behaviours. So how does a shark's mind work? What advanced cognition are they capable of? And why have sharks evolved such advanced brains?
A Tale as Old as Time
Sharks have been around for well over 400 million years and during that time, their brains (just like an other part of their bodies) have adapted in response to a myriad of different "selection pressures". As a result, their cognitive abilities and behaviours have all evolved and advanced in order to help sharks survive in their habitats. These changes have almost certainly contributed significantly to sharks' evolutionary success (Schluessel, 2015).
Today sharks have adapted to fit a myriad of "ecological niches" in many different habitats; from coral reefs to mangrove forests; from offshore waters, to the deep seas, to freshwater habitats in rivers and lakes. Some hunt big marine mammals, others eat microscopic organisms and some forage in packs. Where some are solitary, others have complex social lives; living in large communities or forming dense aggregations. This diversity is reflected by broad variations in cognitive functioning and behaviour between the species (Brown & Schuessel, 2023).
It's All In Your Head
Generally speaking, how cognitively advanced - or smart - an animal is, is related to how big their brain is compared to their body. A bigger animal will generally have a larger brain, but this does not mean they have a relatively big brain. If their brain makes up only 0.1% of their body weight, they are likely not as cognitively advanced as a species where 2% of their body weight is their brain, even if that animal is much, much smaller. The only group for whom this pattern does not hold true is the birds. Their brain structure is very different and so the size of the brain does not necessarily reflect their cognitive abilities (Brown & Schuessel, 2023).
It might come as a surprise to you, but sharks actually have big brains! Across all species of sharks, they generally have a large brain size relative to their bodies, suggesting they should be quite intelligent. The species with the largest brains of all are those that live in dynamic, complex habitats or have complicated lifestyles, that require advanced cognitive functioning. For example, sharks that live on reefs or species that have elaborate social lives (Yopak et al, 2007; Brown & Schuessel, 2023).
When we look at the shark family tree, "Galeomorph" sharks tend to have larger brains than "Squalomorphs". Notably, the hammerheads (known as "sphyrnids") and requiem sharks ("carcharhinids"), like reef sharks, have some of the relatively largest brains. Mako sharks (Isurus species) have the greatest brain to body ratio of any species, implying that they could be the most smart (Yopak et al, 2007; Brown & Schuessel, 2023).
Thinking It Through
Just like dogs or rats, sharks can actually be trained and this means that we can teach them how to do things in the lab, in order to determine how intelligent different species are. These assessments have shown us that sharks and their close relatives are capable of some very advanced cognitive tasks (Schluessel, 2015; Brown & Schuessel, 2023).
Starting with the basics, it is clear that sharks can recognise their environment, identify landmarks and cues, and learn to navigate their way around. They have excellent spatial memories and have easily defeated complex maze experiments (to learn more, check out Making Memories). Port Jackson sharks (Heterdontus portusjacksoni) can even be trained to recognise different genres of music and use these as cues for navigation (see Move to the Music). Bonnethead sharks (Sphyrna tiburo) can even use the Earths geomagnetic fields to build a "mental map" in their minds, which they can use to navigate (for more information, you can check out Animal Magnetism). This is a highly evolved cognitive ability (Schluessel & Beckman, 2012; Keller et al, 2021; Brown & Schuessel, 2023).
This makes perfect sense when you think about it because "spatial learning" would be critical for their survival in the wild. If sharks were not able to learn and remember, how could they go back to safe hidey-holes to avoid predators, or return back to an area where there is a lot of food to eat (Brown & Schuessel, 2023).
Sharks are also capable of "time-place learning", where they can identify a particular area and remember what time of day something happens there. This skill has allowed sharks to learn when fishing vessels or ecotourism boats will arrive, so they can show up promptly and collect an easy meal. In a more natural setting, this ability would be vital for finding food (Brown & Schuessel, 2023).
Sharks that live in groups are able to recognise specific individuals and form something akin to friendships; preferring to spend their time with particular "conspecifics" (members of the same species). This allows them to form strong, stable social groups, providing them protection from predators, and advanced mating and foraging opportunities (seeYou've Got a Friend in Me for more details). As many fishes have been proven to be capable of feeling emotions, scientists also suspect it may even be possible that sharks have feelings of some sort - possibly aiding in social cohesion (Schluessel, 2015; Brown & Schuessel, 2023).
Whatsmore, sharks are capable of learning from others and imitating their behaviours. This allows them to grasp new skills by watching each other, similar to how a child will imitate your actions in order to master a new skill. Believe it or not, scientists have even shown that sharks are able to communicate "social information" amongst themselves; teaching other sharks how to find food or how to avoid being caught in fisheries. To learn more, see The Social Network (Brown & Schuessel, 2023).
Now we come onto the truly mind-blowing stuff... Recent research has shown that sharks are capable of arithmetic. Yes, you read that right... sharks can do maths! Lab studies have shown that they are capable of identifying 'more than' and 'less than', so they have some concept of relative quantities, and stingrays have even been taught how to do addition and subtraction! This might sound bonkers, but logically it makes sense... Understanding amounts is vital for foraging. If you are able to grasp that there were more tasty fish in one place versus another, this gives you the ability to visually identify good hunting grounds. This may be one factor in why sharks are such incredible predators that have survived for so many millions of years (Brown & Schuessel, 2023).
Mindless?
It is not only humans beings and great apes that are capable of remarkable intelligence, and in fact, we are learning more and more that a huge range of animals are capable of remarkable cognitive feats. Where many people in the past thought that sharks were cold or stupid, it is now becoming increasingly clear that that is simply not the case and they may be equally as (or even more!) intelligent than many other clever animals (Schluessel, 2015; Brown & Schuessel, 2023).
Scientists have proven that bamboo sharks are actually capable of mastering discrimination tasks - where they must identify a specific button or plate by recognising a colour / shape / symbol - almost as quickly as dogs can! The spatial learning abilities and orientation strategies of bamboo sharks and stingrays are as well developed as many other fishes, and even some other vertebrates. Freshwater stingrays (Potamotrygon castexi) have even been shown to use tools - something that was thought to be limited to only the most cognitively advanced species, like chimps and corvids (Schluessel, 2015; Brown & Schuessel, 2023).
We already know that sharks are far from stupid, and it is becoming clear that they may be as evolved and advanced as other creatures to which human beings attribute 'intelligence' And yet we have only just started to scratch the surface of what sharks' brains are capable of! As we continue to investigate, who knows what other abilities we will discover that sharks have been masters of all along...
References
Brown C & Schluessel V (2023). Smart sharks: a review of chondrichthyan cognition. Animal Cognition, 26:1. Access online.
Keller BA, Putman NF, Grubbs RD, Portnoy DS & Murphy TP (2021). Map-like use of Earth’s magnetic field in sharks. Current Biology, 31. Access online
Schluessel V (2015). Who would have thought that ‘Jaws’ also has brains? Cognitive functions in elasmobranchs. Animal Cognition, 18. Access online.
Schluessel V & Bleckmann (2012). Spatial learning and memory retention in the grey bamboo shark (Chiloscyllium griseum). Zoology, 115. Access online.
Vila Pouca C & Brown C (2018). Food approach conditioning and discrimination learning using sound cues in benthic sharks. Animal Cognition, 21. Access online.
Yopak KE, Lisney TJ, Collin SP & Montgomery JC (2007). Variation in brain organization and cerebellar foliation in chondrichthyans: sharks and holocephalans. Brain, Behavior and Evolution, 69:4. Access online.
By Sophie A Maycock for SharkSpeak
