Discovery Channel's Shark Week has become wildly popular with one main strategy: making people terrified of sharks and casting them as cold-blooded killing machines (and occasionally making things up to accomplish this goal).
As a result, the network overlooks all sorts of fascinating things we've learned about shark intelligence in recent years.
In experiments, scientists have learned that individual sharks have distinct personalities. They appear to develop closer relationships with certain sharks over others. They can be trained to recognize shapes and colors, remembering how to complete a task months or years later — and can even teach other sharks how to do things.
"Experiments on the intelligence of bony fish have been conducted for decades, but it's logistically been a lot more difficult to experiment with sharks," says Tristan Guttridge, director of the Bimini Sharklab in the Bahamas. "But we're now beginning to catch up — and we're finding that, if anything, they're even more intelligent."
Sharks are social animals — and they make friends
For years, scientists noticed that sharks often formed groups in the water, but it wasn't widely interpreted as evidence of social behavior. "No one really thought that they were forming groups because of an affinity to each other," Guttridge says. "It was thought they were just chowing down on a carcass together."
But his experiments over the past few years with lemon sharks have dispelled that idea. He and his colleagues have determined that in both pens and in the wild, these sharks prefer to spend time in near contact with others, even in the absence of food and predators.
In the wild, he's observed these sharks following closely behind one another for hours, or circling each other in a tight doughnut. By tagging individual sharks and tracking their interactions over time, he found something even more fascinating: They seem to make friends.
"We found that these sharks have persistent partnerships. It's not random who they choose to follow," Guttridge says. "You don't want to anthropomorphize too much, but in reality, they had preferred buddies."
Other species seem to be similarly social. Great whites, for instance, appear to have social hierarchies based on size and sex — and they use the underlying relationships to hunt prey cooperatively. As Leonard Compagno, director of the Shark Research Institute, told Smithsonian, "One great white will draw the attention of a seal, allowing another to come from behind and ambush it."
Sharks can be trained to recognize shapes and colors
Shark training experiments go back to the 1970s, but most of this early work involved negative conditioning, like training a shark to associate a flash of light with an electric shock.
More recently, though, scientists have begun probing sharks' abilities to be trained in more complex ways — and they've found they're quite capable of it.
"You can train a shark, just like you can train a dog, to touch a target and get a piece of food," Guttridge says.
Much of the work has been done by Vera Schluessel, a biologist at Germany's University of Bonn. Initially, she trained gray bamboo sharks to recognize particular shapes — for instance, pushing their snouts into squares but not other shapes on a screen to get food.
She's also trained the sharks to navigate a simple T-shaped maze. Over the course of five to 10 trials, they learned to consistently turn either left or right — associating the correct direction with specific shapes and colors on the walls:
Sharks have surprisingly long memories
Schluessel also tested the sharks weeks or months after both experiments. They remembered the maze for up to six weeks. With the shape experiment, they did even better: The majority were capable of recognizing the correct shape six months later, and some where even able to do so after nearly a year had passed.
Guttridge, meanwhile, has carried out conditioning trials with Port Jackson sharks, training them to associate LED lights or streams of bubbles with food dropped into their tank. After repeated trials, the sharks learned to search for food once they saw lights or bubbles and when retested up to 40 days later still displayed the same behavior. Guttridge speculates this sort of spatial memory might be useful for remembering feeding spots with plentiful prey.
Sharks can teach each other
In a more involved training experiment, Guttridge found that lemon sharks are even capable of teaching other how to solve these sorts of tasks.
To start, he and colleagues taught a group of sharks how to get a food reward: by swimming back and forth between a pair of delineated areas in the water and bumping a target with their nose each time. Then, they paired each shark with a new one who hadn't been trained at all.
"You could see the naive one following the trained one, and starting to bump the target and move between the zones," Guttridge says. Then they removed the trained sharks, timed the other ones, and found they figured out the task more quickly than sharks that hadn't had a teacher.
Sharks have individual, distinct personalities
One of the main ongoing projects at the Bimini Sharklab involves tracking the behavior and personality of specific sharks over time. In one experiment, a group of wild lemon sharks are collected in large pen in the water and individually tagged. Scientists monitor their interactions with each other, then release them, and catch them to repeat the same process weeks or months later.
By doing so, they've found that, much like humans, some sharks are relatively extroverted and some are more introverted. "There's consistent, individual variation in different traits," Guttridge says.
In another experiment, individual sharks are taken into a large pen split into zones, and researchers monitor how many zones they explore and how quickly. When they repeat these trials months or years apart, they similarly find that some individual sharks seems to be more likely to explore their surroundings, while others tend to be more timid.