Click here to watch the TEDTalk that inspired this post.
Sharks have been ruling the world's oceans for 400 million years. That's a couple hundred million years before Pangea busted up and the continents started slipping all around the globe! Sharks were on the scene way before the age of dinosaurs, birds or mammals, and long before humans appeared on the face of the earth to wreak havoc with every other living creature in the natural world and increasingly invade shark habitat and complain about sharks being sharks. Ancient sharks were eating odd sea creatures that are now extinct; do you think they are flummoxed by stripes?
In contrast to most animals, people rely heavily on vision. Most animals rely on other senses that work much better in their environment. Vision under the ocean, if you haven't actually been underwater outside a swimming pool, is typically lousy. Other senses that work very well in water, including some that only work in water, are what sharks and other marine creatures rely upon. The sense of smell and taste, for example, work fantastically well in water, as every fisherman knows.
Sharks and other fish also have a unique sensory system that we do not have -- the lateral line system -- which allows them to sense tiny water displacements created by an object moving through fluid, such as a surfer in a striped wet suit paddling on the surface.
Sharks, unlike most fish, have an even more remarkable ability to detect prey. They can sense the minute bioelectric field created by living creatures in seawater -- people included. This special sense of electroreception, not vision as the TED Talk asserts, is what guides the shark in the final moments of attack. If they used their eyes as their primary sense, as stated in the TED Talk, all they would see is the inside of their eyelids. Sharks close their eyes to protect them as they tear into their prey. I've seen this in my own field research where we found that blue sharks would divert from the actual food source at the last moment and attack an electrode a meter away emitting a weak field like the one surrounding any fish. Electroreception works in the dark, in murky water and even when prey are buried under sand. Imagine -- sharks were using electricity for targeting prey 400 million years before Ben Franklin got a clue by flying his kite in the rain.
The "science" in this TED Talk is also problematic. Where's the control experiment? Both the striped and the unstriped target need to be presented to the shark at the same time so each one has equal chance of being selected by the shark. Moreover, the target needs to accurately model an actual prey item, such as the ones that wear Speedos, and generate all the sensory stimuli sharks enjoy.
And what are the objective criteria? "This is the banded one," Jolly says describing the shark probing their plastic bait-filled barrel. "Where it's more tactile, it's more investigative, it's more apprehensive and shows a reluctance to come straight in and go."
I'm not sure this is as conclusive as we're led to believe. I've seen many shark attacks and what impresses me is how wary and cowardly sharks are. They typically circle and check out their prey from a safe distance, then ease in closer to gain more information. Then, they frequently probe it in a swift passing bump before something switches in their brain and they attack in a way that the word used to describe sharks at supper portrays -- a frenzy. At that point the sharks mob and chomp down on anything, including the hull of your fiberglass boat.
In experiments on electroreception done in the middle of the night off the coast of Woods Hole, Marine Biology Labs, I remember several large blue sharks distracted by a sea turtle from the experimental apparatus suspended beneath our boat. The sharks circled. Then, one bold one finally swept in and bumped the creature splashing desperately on the surface. Then, another shark charged in and clipped off one of the turtle's front flippers. Then, another did the same to the other flipper, then the other flipper was amputated. When the animal was nothing but a helpless creature that could not possibly threaten the sharks, they all charged in and the water boiled with froth and blood.
Sharks are not stupid. They probe the world with many different sensory systems and they "see" it in exquisite detail that we will never know, using only our eyes, ears plugged with water and no sense of smell. If you present sharks with a plastic barrel full of bait that lacks all other natural stimuli that excite their senses and especially lacking the primary sense of electroreception, how do the results with painted plastic barrels relate to a real prey item? The stripes do nothing to the shark's sensitive electrosensory and lateral line systems. Sharks are not that stupid. People...well that's another kettle of fish.
Dr. Fields is a neuroscientist with an MA degree in Marine Biology from San Jose State Moss Landing Marine Labs, and a PhD degree in Biological Oceanography from the Scripps Institute of Oceanography in San Diego. He has studied electroreception and seen several white sharks in the wild but has never been attacked by one. On the contrary, as a starving graduate student he and his wife were sustained one winter by eating one the size of a truck. Why let the specimen go to waste?
We want to know what you think. Join the discussion by posting a comment below or tweeting #TEDWeekends. Interested in blogging for a future edition of TED Weekends? Email us at firstname.lastname@example.org.