Long term study of the behaviour of individual sharks has shown that they are not just acting on instinct. They are thinking and highly intelligent, and likely conscious too.
So as the Year of the Shark in 2019 begins, here is a review of how their actions reveal some of their mental states.
The usual methods for studying sharks are through tagging and dissection rather than through observing their actions underwater. However, direct observation of the actions of many individuals is the method, termed “ethology” normally used to study wild animals on land. So over a period of fifteen years, I searched out and observed the reef sharks on different islands in the South Pacific and for seven years studied the population of blackfins intensively as individuals. By recording their actions I was able to access a dimension of their lives that had not previously been documented. My records ultimately included 581 individuals and I could recognize 300 different sharks on sight.
Their complex behaviour soon showed that the sharks were using reasoning, rather than reacting automatically to their environment as had been assumed. Cognition, the process of knowing through thinking, is the term used for thinking in animals. An animal shows that it is using cognition, rather than trial and error, when it must have referred to a mental representation in order to act as it did. Many life forms, including invertebrates, are increasingly found to be using cognition in their daily lives, and cognition in fish has been well studied.
Wild animals are always vigilant, always on the lookout for danger, and sharks are no different. Whenever anything was different about my visit, whether it was in a different place or at a different time, their behaviour became more cautious.
All of the species of sharks I observed use the visual limit to conceal themselves. Once out of sight, they continue to pay attention from beyond visual range, by listening and through their lateral line sense. Occasionally they pass into view to look. If the shark is interested enough, its approaches bring it closer each time. Some species, such as tigers, pass above the object of their interest—for example, a diver—while others tend to approach horizontally.
In the case of blackfin reef sharks, the approach becomes more direct with each repetition and the shark turns away at a more acute angle each time. Its closest approach may bring it up to the diver’s mask before it turns away. This close approach is occasionally done very fast in order to intimidate, for example when the shark is trying to force a spear fisherman to give up his fish, however, the sharks who came to know me best would perform it slowly, one after another, when I first arrived, as if it were a sort of greeting.
The older female sharks, which are the largest individuals, were the shyest. Elderly blackfins would often linger out of visual range, making few passes into view and never coming close, while excited bands of males coming into the shallows to mate after sunset would zoom straight up to me on first meeting.
Other species tended to approach by making repeated passes in a straight line, coming closer to the diver each time, but rarely closer than two metres.
On the few occasions that I brought another person with me, the sharks sometimes vanished beyond visual range when the visitor appeared underwater. Many minutes would pass before they came back and they would arrive in long lines led by the boldest among them. In single file, they would glide straight up to the stranger, after which they milled around and if I had brought food, they would not eat.
This behaviour demonstrated their alertness to changes, and their ability to make quick decisions based on unexpected findings. Memories of events that can be called upon for decision-making are called declarative memories and are considered to be evidence that the animal is conscious.
Fishermen who complain that shark feeding dives cause sharks to harass them have failed to understand this crucial point―sharks easily discern the difference between a shark feeding event and a spearfisherman. It is the fishermen themselves who attract sharks, by holding dying fish underwater and trailing scent.
Knowing Others as Individuals
Individual differences marked each shark’s behaviour. Each one had a unique pattern of roaming, under the dual influences of the lunar phase and the reproductive cycle. Some were nearly always present in their home ranges, while others travelled for months at a time. Individual sharks demonstrated different rates of learning, and they varied greatly in their responses to different situations. They had complex social lives and their behaviour was flexible depending on the circumstances.
The sharks recognized each other as individuals, which is the prerequisite for the complex social lives in which cognition is most evident. Blackfins travelled widely, and tended to go with preferred companions. At times they joined with others residing in the regions they passed through. There was always excitement when travellers and residents met, and since they are not territorial, there was no aggression. They would follow each other and swim side by side for long periods, often in a state of excitement, before the companions moved on.
Companions were individuals of the same gender, and usually the same age as well. Some sharks usually travelled alone, some always with the same companion, and others changed companions. Due to the circular paths in which they move, they repeatedly crossed each others’ scent trails, and thus remained in loose contact as they roamed, together, yet not usually within visual range.
As far as I was able to determine, such friends came from the same region. The reef sharks were acquainted with the other individuals whose home ranges overlapped theirs and their travelling companions were usually neighbours at home.
Bonnethead sharks, too, have been shown to recognize each other as individuals, and at least some species of sharks and rays choose their mates, providing further scientific evidence that individuals know each other.
Memory and Learning
Learning plays an important role in the lives of sharks, as has been well documented. Learning is closely involved with memory, and the sharks I knew showed an ability to remember events far back in time. Familiar sharks recognized me in the lagoon as much as two years after their last meeting with me, and their behaviour, of greeting and travelling with me, was unchanged.
Like people, different sharks had different rates of learning. For example, among those who accompanied me most often, one of them never learned to take a treat I threw for her, while only a few caught on immediately without practice.
Often a shy shark who appeared briefly in visual range would suddenly pass close behind me, but dart away if I turned and saw her—she had come to look without being seen. Sharks easily understood the direction in which a person was looking. In other ways, too, they showed that they were aware of whether or not they could be seen. When I was with another person, for example, they would swiftly approach for a closer look when we raised our heads above the surface to talk.
Once I was swimming with my step-son, and he climbed on a dead coral structure to look around above the surface. The shark who was accompanying us swam over to sniff his legs, and with his head above the surface, the boy never saw her.
Sharks also surprised me by swimming between my face and hands when I was drawing their dorsal fins for identification purposes; this never happened when I was paying attention to them. One unusual shark passed me nearly every time I went to the lagoon, drifting by from left to right, always and only when I was looking the other way. She did this for eight months before relaxing her vigilance and moving around me more freely.
Always on the alert, the sharks used their awareness of whether or not a person could see them to their advantage.
Therefore, it is not surprising that you never see the shark who bites you. As with other predators, it is best to face them, and pay attention to them when you are with them. But, that said, shark bites are very rare. Sharks were the only wild animal with which I was in intimate contact for many years, and who never bit me, either through accident or irritation.
I eventually concluded that sharks have an inborn inhibition against biting companions, or others of their own species. This is well known among species that have evolved dangerous weapons, though not in humans, the only large predator who invented, and did not evolve, its weapons. During fights, for example, no wolf or dog will bite another who rolls on his back in submission, but humans will kill people who are begging for mercy.
Attention, Curiosity and Observation
The sharks were very curious and investigated anything new. If a coconut floated across the surface, one would notice and rise to sniff it, followed by the others. They would often follow me for long distances, sometimes for hours, while remaining hidden beyond visual range. From time to time I checked to see who was with me by suddenly stopping, whereon they came into view and I could check their identities. It was surprising that they would remain concentrated on one thing for such a long time.
Sometimes unexpected events revealed patterns I might not otherwise have seen. When one of the sharks became ill, each evening I tried a different tactic to give him a piece of food in which antibiotics were inserted. The other sharks seemed to anticipate each of my attempts, and their actions made it very difficult for me to medicate him.
One of the tactics they used after several nights of missing out on this piece of food, was to wait beyond visual range. When the time came to medicate the sick shark, and I went to the kayak and threw his chunk of food into the water, seven sharks, whom I thought had left an hour earlier, soared in, and the fastest one snatched the treat in mid-water.
Since they had been out of view, they had based their decision to act on a signal they had heard. They had understood the sounds of me getting the treat and throwing it, and their actions were effective because one of them did get the food!
This example shows their ability to predict something that might occur in the future and to concentrate on it. Cognition is indicated because they must have held a mental representation of possible food coming, the signal that would trigger its imminent arrival, and what they planned to do when it came.
It often seemed that the sharks tried to be one step ahead of me. In long-evolved predators who catch swift and evasive fish for a living, the strategy of watching and waiting, and trying to predict from past experience what the prey would do next, could well have been selected for.
Cognitive ethologist Donald R. Griffin pointed out that when an animal hid from view, it was demonstrating self-awareness. He described how Lance A. Olsen had reported that grizzly bears sought places from which they could watch hunters while remaining hidden. Other observers had reported too, that bears tried to avoid leaving tracks.
The researchers concluded that these bears were aware of being present and observable, as well as creating effects―their tracks―through their movements, which could be seen by others. The sharks’ habitual way of remaining concealed beyond visual limit until an opportunistic moment, or approaching from behind to avoid being seen, is in the same category of behaviour and indicates that they are aware of being present and observable.
This is the reason why the so-called ‘shark counts’ that divers are asked to participate in, have no scientific validity. Since sharks are either attracted to divers or avoid them, the numbers of sharks seen by divers are not representative of the true numbers on the reef. Where sharks are habituated to divers and come to see them, such counts may give the impression that there are many sharks, when actually, their numbers are few.
Further, once the information is published, the sharks are vulnerable to being fished for their fins.
Occasionally reef sharks would flip on their backs to wriggle in the sand, presumably to scratch or to free themselves of parasites. On other occasions, a shark would turn to whip the side of its body against a sandbank. The floor of the lagoon was made up of sand interspersed with reef flats and coral, and the sharks invariably chose only sandy places for such manoeuvres.
Sometimes a shark carefully positioned himself to use a smooth, flat surface of dead coral on which to rub himself. Apparently, he had intentionally surveyed the environment and chosen a suitable structure to use. He must have held a mental image in mind of what he wanted, and referred to it while looking for a formation of the right shape.
Though this may not seem to be very impressive in terms of thinking in sharks, the availability of surfaces to use in this way does not mean that the animal will realize how they can be of benefit. For example, mynah birds (Acridotheres tristis), and junglefowl (Gallus gallus), the wild ancestor of domestic chickens, both spend much of their time foraging for insects on the ground, and both have strong feet for walking. However, mynah birds have not discovered that they can use their feet to help them uncover these insects, while junglefowl do so instinctively.
I was lucky to witness a clear decision made by two sharks, between two possible choices. One day near my study area, I saw the fins of many sharks slicing the surface and found a spawning event underwater. Sharks were gliding among the clouds of dancing fish, occasionally snapping one up. Two blackfins came over when they saw me, and returned from time to time to circle me over a fifteen-minute period. When I left and travelled another kilometre into the lagoon in my kayak, these two sharks followed from the spawning site.
They decided to follow me even though they had not seen me for several months, and they made the choice that was based on a mental reference—a thought or memory—that sometimes I brought food. Yet, they were already in a situation in which they could see, hear, and smell food, moving in a stimulating way, and I had not fed them in that location before. This decision to leave, based on a memory many months old, indicated that they must have made such memories, and referred to them, a clear act of cognition that indicates consciousness.
I could not see evidence of communication between sharks except through body language. Yet occasionally, companions acted in concert, leaving the other sharks, and swimming in formation to perform a specific act together. How they communicated the decision to do this was not clear, but likely body language played a role.
In his book, The Secret Life of Sharks, Professor Peter Klimley described how great white sharks ritualize their conflict when a seal that one of them has killed comes under dispute. Each slaps the water at an angle with its tail, and the shark who raises the most water and blasts it farthest wins the prey. For this ritual to be effective, each shark must view its opponent’s gesture as a communication, and understand it, since the winner gets the seal without a fight, which could badly hurt both sharks.
Sharks often passed the same place at the same time repeatedly. One young visiting male passed by my observation post about five meters to the right, between ten and fifteen minutes after sunset each night for several weeks. Each time, he saw me and came for a closer look, then turned and went on his way.
Another rare visitor’s first four visits, though months apart, occurred precisely at the moment that the sun touched the horizon, four days before the dark of the moon.
Intrigued, when one of the residents who had habitually met me on my arrival in the lagoon, began coming instead at the end of the feeding session and missing out on the food, I kept careful track of the time of her return. For reasons known only to her, she had suddenly begun to spend her days in the ocean. Over a period of many months, she returned about ten minutes before sunset, night after night. Sometimes, she still met me when I arrived at the study site, yet other times, I saw her return from the sea when it was nearly dark and pass in the distance without coming to the feeding session.
Besides illustrating a remarkable ability to follow a daily schedule, and yet be flexible about it, her actions indicated that she had not become dependent on my weekly feeding sessions, though she had known about them since she had been a juvenile.
The sharks seemed to have no trouble catching a fish when they wished to, and often came to the feeding sessions only to socialize. Resident sharks routinely left for months at a time, and visitors did not remain in the area because of the food. Though many came to my feeding site at the proper time, their long-term schedules were unaffected by the few scraps I provided once a week to facilitate my observations.
The resident sharks learned in time that the fish scraps I brought to the feeding sessions were in the back of my kayak. Though this species has not been documented breaching the surface to eat or to look around, these sharks found that the food could be accessed by leaping from the water, and leaning towards the boat, while snapping at whatever they could locate. The sound of their jaws snapping shut made loud clapping sounds, and some of the kayak’s straps were cut, punctured and sliced by their sharp little teeth.
This behaviour pattern was a new foraging technique they had discovered, that was initiated by one or two sharks and instantaneously copied by the others present. They used it from then on. This discovery happened twice, in different locations, under different circumstances, with different groups of sharks, and is an example of social learning, which is basic to the development of culture.
Under normal circumstances, the space above the surface is not something that these sharks would have reason to consider. But they were presented with an artificial situation in which I came from above the surface and returned there, and so did the food in which they were interested. They would doubtless have stored memories about the surface from the occasions, particularly when they were small, when they swam through it or up against it while chasing a fish, though it is unlikely they could have formed more than a vague impression that there was a space above, from such brief events. Yet, their behaviour suggested that they were aware of a volume above the surface in which things could exist, and from which I came and went.
A question in cognition is whether an animal knows that something continues to exist when he or she can no longer see it. An object apparently ceases to exist for dogs, for example, when it disappears from view. So few people would agree that sharks could understand that I was in my kayak, even when I had just left their company and climbed into it. Yet they were aware. Indeed, the many ways that sharks took advantage of the opportunity to hide beyond visual range, strongly suggests that they understood very well the idea that something continues to exist, in spite of being out of their view.
Sharks have exquisitely coordinated senses, and their behaviour indicated that they used this sensory input alertly to make moment-to-moment decisions, and respond flexibly and appropriately to changing circumstances. They remembered the events in their lives and referred to these memories in decision making. They were curious, but cautious, and learned quickly. Their versatile behaviour, individual differences, and different ways of handling various circumstances were not indicative of a set of stimulus/response reactions.
I have observed sharks underwater in the Bahamas, including bull and tiger sharks, and found that their behaviour was remarkably similar to the behaviour of the requiem sharks I had known in Polynesia. This is to be expected since sharks have been evolving for four hundred twenty million years, and many species travel widely and are found around the globe. The essential qualities that sharks evolved to be so successful would already have developed in the ancestral forms before they evolved into modern species occupying the ecological niches we know today.
Though fish may seem primitive when looking down on them from the altitude of Homo sapiens, in fact, they are highly complex and evolved life forms. And no brain is simple, as anyone who has observed the activities of a spider will appreciate.