The Social Life of Sharks

Posted on October 27, 2011
Written by: Mary Chipman

Image Gallery

In her book, My Sunset Rendezvous, Crisis in Tahiti, Ila France Porcher describes the social relationships between the various blackfin reef sharks (Carcharhinus melanopterus) that she observed over a period of seven years during her ethological study. What is interesting and unique about her study is that she was able to interact with the same individuals over an extended time period, identifying sharks by drawing their distinctive fin patterns, and naming them. It would have been impossible to keep track of hundreds of sharks without naming them, and the names have the effect of making her account of their social interactions become very personal and immediate. As one progresses through reading the book, certain sharks come to seem like old friends who you might run into on a street corner or at a café.

Ila observed that certain female sharks tended to travel together, arriving together in her study area at certain times of the year, and leaving together1. The way that these sharks appeared to know each other as individuals suggested a surprisingly high degree of social organization. Over time, Ila identified distinctive personality traits associated with individual sharks, and as she became accepted by the sharks, a few became "friends" in the sense that they sought her out and seemed to enjoy interacting with her.

Ila's rich and varied account of the social relationships between herself and the sharks she studied reveal new information about the closed world of sharks. Most of us who are fortunate enough to dive with sharks travel to a remote location, dive with a variety of different sharks, and leave. The sharks tend to blur together, making it impossible to pick out relationships or patterns of behavior between sharks, and we are not able to interact with the same sharks on a regular basis.

Sharks have swum the oceans for almost 450 million years2, whereas modern humans have been around for a mere 200 thousand years, depending on when you start counting. Up until the last few decades when scuba became popular, our relationship with sharks has been limited mainly to the surface of the ocean, blurry-eyed free diving, pulling them up as a food source, or for an unfortunate few, being bitten by one of the larger species. Humans in various cultures had varying relationships to sharks as deities or a source of food, but no species of shark has had any kind of ongoing, co-evolutionary relationship to humans. We simply never existed in their world until the advent of scuba, venturing into the ocean too infrequently to be a reliable meal ticket. They have no idea what we are, in our wetsuits and bulky scuba tanks, floundering clumsily along the reefs, or sitting eagerly on the bottom clustered a safe distance from the bait box.

As two species separated by our inability to exist in each other's environment, sharks and humans have no shared history of interacting with each other, picking up on each other's signals and body language, or interpreting the subtle signs that indicate peaceable intentions, or attack.

In order to protect ourselves from large predatory species such as white sharks (Carcharodon carcharias), we are slowly unraveling the sharks' body language and cognitive abilities3, correcting the long-held assumption that sharks were too primitive and stupid to learn anything. Sharks have proven to be curious and quite smart, which isn't surprising given their long evolutionary lineage. A stupid, incurious species would not have been able to survive multiple global extinctions. Sharks have had to uncover and exploit new habitats and food sources, and also resolve conflicts among their own kind. They needed to recognize themselves in a social context relative to others and to cooperate and interact in mutually beneficial ways.

There is much evidence that various species of sharks have evolved social hierarchies and ritualized behaviors to eliminate conflict and potential damage to conspecifics (sharks of the same species). One such example is white sharks resolving conflicts over food with non-violent agonistic displays3, such as tail slapping behavior where the shark that creates the biggest splash wins. Sharks possess an excellent sensory system that provides them with visual, acoustical, chemical and electrical information about their environment4. Sharks doubtless use these senses to calibrate their social interactions both with other sharks and with divers, picking up subtle electrical and chemical clues in their social decision-making processes.

The rich sensory world of the shark is lost on us humans, who are limited primarily to our vision under water. In addition, our vision is impaired and partially obscured by a face mask, and we need to turn our heads around, up and down in order to assess whether a shark is approaching and what its intentions might be. On land, when interacting with terrestrial species and other humans, we send and receive both overt visual cues expressed as body language, as well as subtle visual cues in micro expressions, which help us form social bonds and avoid threats5.

In My Sunset Rendezvous, Ila reports that sharks would often circle just outside of her field of vision, and that they exhibited different behaviors when a stranger entered the study area. They clearly recognized her, and exhibited both caution and curiosity with the stranger. One can only wonder which sensory cues sharks might use to determine whether it is safe to approach a stranger, even when accompanied by someone they have already accepted.

In addition to our awkward swimming style under water, we emit audio and electrical signals with our muscles, including our heartbeats, and we may even emit chemical signals in our pheromones. It seems reasonable to assume that sharks who become habituated to divers learn to read a wide variety of human emotional states over time. Jim Abernethy has been diving with the same population of sharks over many years, and inHow to Friend a Tiger Shark: The Making of a Supermodel, Jim describes how he gradually overcomes the natural reticence of the wild tiger sharks (Galeocerdo cuvier) he interacts with, building trust over an extended period of time. With the sharks' exquisite senses, it is not unlikely that they "read" Jim's emotional state, which is one of respect and affection, much the same way you do when a person enters a room – you usually know instantly if they are happy, sad, angry, or fearful. The fact that Jim can even get close enough to remove hooks without being attacked is evidence that an unspoken social contract of mutual trust and respect is possible between people and large, potentially dangerous shark species.

In this video clip Emma finds Jim Abernethy after two months walkabout:

Emma finds Jim Abernethy after two months walkabout

For more on Emma, see Tiger mom-Emma the shark) The fish attached to the white jugs shown in the video release a scent trail into the water toattract the sharks, but Emma clearly prefers the social interaction with Jim over investigating the bait. Jim and Emma display the same degree of mutual affection and enthusiasm for each other that you might have interacting with your pet dog after a long absence. Lest you think that forming a social bond with a wild shark comes easy, consider that for the last decide, Jim has averaged 11 months a year on his liveaboard, going to the same place, and diving with the same group of tiger sharks every day.

During her study in French Polynesia, Ila consistently visited the same general area and, out of the 600 blackfin reef sharks she identified, she became "friends" with the sharks who lived in the lagoon, and was recognized by others who passed through more infrequently. Ila proved that the sharks she studied are not at all the cold and vicious creatures portrayed in the media. Others should be able to validate her findings with similar studies, given time, patience and a kind attitude. However, few people can afford to spend the time necessary to gain the trust and respect of a wild animal—it's not an experience that the casual day tripper or resort diver, or even a scientist on a field trip, could hope to replicate.

Whatever social contracts may evolve between human and shark are fragile, and trust can be eroded or broken. Ila France Porcher describes an instance of this in My Sunset Rendezvous when she altered her routine towards the sharks she was studying in order to care for a sick shark and ended up alienating the other sharks. Scientists avoid resorting to anthropomorphizing animal behaviors with emotional descriptions such as "friendship" or "love" or "anger". However, our vocabulary is limited when describing our own emotional and cognitive responses, so we have no alternative but to fall back on familiar terminology when describing the social behavior of sharks. Ila writes that:

"the violent slamming of the boat always appeared as a negative emotion, something akin to rage, expressed towards me. I kept coming back to the conviction that the seed of change had been planted when, day after day, I had tried different ways to get medicated food to Meadowes [the sick shark], sometimes only bringing scented water, but no food for them. They had known that I had food but that I was not giving it to them, and now they behaved as if they thought I could be tricky."7

This incident was just one episode in the evolution of Ila's relationship with the 30-odd resident sharks, not the final outcome. Over time, their suspicion faded. Ultimately we can only guess what a shark knows, senses, feels or thinks, because we can only interpret their behavior within our own narrow context. Similarly, it seems clear that after accepting Ila, the sharks had no way of interpreting her altered behavior in a human context, only in their own. Ila also observes in No Bite Reflex in Sharks? Surprising Observations from Tahiti that the blackfin sharks she studied never bit or nipped at her, or each other, the way that terrestrial species are likely to do as a way of expressing aggression or negative emotions.

The fact that social relationships between humans and sharks can be established at all is fascinating, and worthy of further study. Ila's blackfin reef sharks and Jim's tiger sharks represent the only two instances that I am aware of where humans have been admitted into the social world of sharks, forming relationships, and yes, friendships, with individual sharks over many years. Sadly, Ila's sharks were killed for the shark fin trade, and only survive in her marvelous book, My Sunset Rendezvous: Crisis in Tahiti. Fortunately, however, the tide now appears to be turning toward protecting sharks, banning the shark fin trade, and establishing shark sanctuaries. As we work to ensure that shark populations can rebuild, we can also hope that in the future there will be many more opportunities for humans to study the social behavior of these marvelous, ancient creatures who seem willing to get to know us too.

References

  1. Porcher, I. F., My Sunset Rendezvous, Crisis in Tahiti pp. 342, 444 and 557.
  2. 450 million years of sharks.
  3. Instinct and Learning in the White Shark http://www.elasmo-research.org/education/white_shark/instinct.htm
  4. Guttridge, T. L., Myrberg, A. A., Porcher, I. F., Sims, D. W. and Krause, J. (2009), The role of learning in shark behaviour. Fish and Fisheries, 10: 450–469.
  5. Ekman, Paul. "Lie Catching and Micro Expressions" The Philosophy of Deception, Ed. Clancy Martin, Oxford University Press, 2009. Google books:http://bit.ly/mQjobg
  6. You can see more examples of this behavior in the recently-released This is Your Ocean: Sharks.
    Read about Emma's recent pregnancy in Tiger Mom: Emma the Shark
  7. Porcher, I. F., My Sunset Rendezvous, Crisis in Tahiti pp. 316.