IM Interview: A Shark's View of the World

The scoop: Sharks are not only misunderstood, but also possess sensory abilities that seem almost magical. Did you know, for instance, that some sharks can feel the Earth's magnetic field and use it to navigate? Shark researcher Jelle Atema chats with me about this and other things you wouldn't expect of the oceans' ancient and most infamous predators...

LarryO': hello. I see you now

jelle.atema: where do I see you?

LarryO': That's the chat window. We're chatting now!

jelle.atema: In that little box?

LarryO': yup

jelle.atema: OK we are on

LarryO': You can enlarge it by clicking on the little diagonal arrow above the text box

jelle.atema: better

LarryO': Great! First of all, let's start with where you work and what you work on.

jelle.atema: I am a professor at Boston University and a scientist at the Woods Hole Oceanographic Institution. I work on shark sensing, lobster communication and population structure, and reef fish sensing. All underwater sensing is fair game but I specialize on chemical sensing and flow detection, closely linked information channels.

LarryO': That's a lot. I'd love to get into lobster communication if we have time. As for sharks, is there anything that can be said about sharks in general and their senses? Or are they too varied?

jelle.atema: There are many species of sharks and they all do different things, some are more visual, others more electrosensory and some more olfactory. We work with the smooth dogfish as an example of a small shark that seems to be using all of its senses for food localization. My impression is that sharks in general have very acute sensing abilities that helps them be such efficient predators.

LarryO': So speaking about the smooth dogfish then, how do they sense their world? Is there any way for a human to grasp it?

jelle.atema: With some imagination I think we can grasp underwater sensing except electroreception. Any diver knows the limits of underwater vision even in the clearest water; this is the result of light scatter as in a fog. We also experience hearing underwater and have a problem knowing the sound direction, a problem due to many factors but one being the speed of sound which is 5x faster in water.

LarryO': Water is pretty foreign for us. We're sort of blind and deaf down there compared to a shark, right?

jelle.atema: Smelling is essentially not different in air and water strange as it may sound: molecules are transported by currents (wind) and reach their (our) nose where one identifies the kind of odor it is, that is: who or what produced that odor, an identifier for the source of the odor. To locate odor we all need to use other senses, primarily flow detection. We are not so good at this but imagine standing on a cliff and pointing your nose into the wind...you will be turning your head all the time to accommodate the slightly shifting wind directions. These are caused by turbulence; following the mean flow of air or extracting a mean direction from the turbulence is the art of many animals that depend on odor to locate food or home or mates.

Electroreception we must try to imagine as the ability to "see" at close distance the shape of a "vortex" leading directly into the electric field generator: a living fish (or human). Sharks and some other animals can sense this at distances of say 3 feet; in complete darkness and without other sensing they know where to direct their final strike on the prey. It can be camouflaged and buried under sand but the electric field is there and gives the prey location away. It only works under water due to conductivity.

LarryO': I remember something at an elasmobranch meeting about this electroreception perhaps being the reason hammerheads have such a strange-shaped head -- it's more of an antenna. This related?

jelle.atema: Correct. The very many pores of the ampullae of Lorenzini allow the animal to reconstruct the shape of the electric fields they encounter. From that shape (I simplified it into a vortex) they can determine how to steer toward the prey. There is a second electrosensory function besides prey detection: extracting earth magnetic field information through "induction", the close link between electric and magnetic fields as discovered by Faraday. Changing magnetic fields cause electric currents that sharks can detect. It allows them to determine magnetic direction and magnetic field variance that can be helpful in navigation over large distances.

LarryO': Wow! So sharks really know where they are. They must have a pretty interesting feel for their location. Seems like a lot of going on, yet sharks aren't known for their large brains. How to they process all this information?

jelle.atema: You'd be surprised by a shark brain! Among fish they are actually quite large and what animals can do with small brains always surprises me. Take a look at a lobster brain. A small pea between the eyes. Yet their sensing and social behavior is amazing. Did you know they can remember the individual odor of another lobster after a 10 minute fight? And remember it a week later after having interacted with may other lobsters. They also can learn the structure of their environment with all its shelters and inhabitants in a matter of hours. So what do we need such a large brain for?

LarryO': Ha! I guess we just have unnecessarily swollen heads in more ways than one. That is amazing about lobsters. I'm always amazed at how "intelligent" even insects and spiders are. Fascinating stuff.

jelle.atema: Besides chatting with you personally, what is the audience for our conversation?

LarryO': General public. We tend to get a lot of men between 25 and 50, in particular, but it's pretty broad. Any misconceptions about shark perception that you'd like to dispel for readers?

jelle.atema: We must keep emphasizing that sharks are not a major threat to humans, whereas the opposite is unfortunately all too evident: we are wiping out sharks at an alarming rate. The number of shark attacks world wide is very small and often the result of human negligence and incompetence, swimming in areas that are theirs and areas where humans know nothing and thus expose themselves to danger. Fortunately the tide is beginning to change and I am getting more and more students , young students, who are fascinated by sharks and want to work with them and understand them. I am quite happy to help out here. They are beautiful animals as you see them in their own environment. In addition I am learning from them how we humans could sense the environment with application in robotics and navigation. We also learn from animals what kind of information exists under water. The ocean is a most complex and dynamic three-dimensional environment even when all we see is "water". We cannot smell the differences or sense all the subtle water flows that inform animals that live there.

LarryO': I get the impression that even when I scuba dive, my experience of the underwater world is utterly impoverished compared to what sharks sense. Glad to hear that there are young folks so interested in sharks. That's a nice change. So, if you have a few more minutes, I'd like to get a quick list of shark senses that I'll use to put together a slide show on the matter. If you have any sources you would like to refer me to, that'd be great and much appreciated. By sources I mean papers, etc.

jelle.atema: Olfaction, taste, lateral line (=flow detection), vision, hearing, electroreception (including electromagnetic induction).

I think some key (older) papers are by Kalmijn on electro reception and lateral line. My paper with Jayne Gardiner deals with the critical function of flow sensing to locate an odor source (seeming contradiction, but I referred to it in our chat). Of course there are so many. If you want I can send you the bibliography of my shark grant with Bob Hueter and Phil Motta.

larryO': That'd be great! Just email it, if you can. I appreciate your time this morning on this. The whole thing ought to be posted online (with copy-editing done) in two weeks. I have my work cut out with the slide show. Thanks and have a great day.

jelle.atema: Thank you too. I have little time this time of year but happy to participate. All the best.

Article posted July 27, 2009.

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