Shark Week’s Not Really My Thing …
So this weekend, I saw my first ever episode of Shark Week. And it was all right. Interesting, if a little heavy on the bloodlust and pointy teeth.
But Shark Week did give me the perfect excuse to call up shark expert Dr. Jelle Atema, of the WHOI (also BU), one of my top two favorite marine bio centers ever. And take it from me: picking the expert’s brain is even more fun than watching a drama-heavy shockumentary with an unnecessary number of Jaws refs.
Here are just a few of the things he had to say:
The electrical sensitivity mentioned in the Shark Week episodes 1 and 2 is more amazing than they show. Atema was on the team that first discovered this extra sense that sharks possess. How does it work? Sharks have an elaborate series of small canals called ampullae of Lorenzini dotting their faces, each canal filled with a clear jelly (which will, by the way, leak out if you squeeze a shark head hard enough). The jelly acts as a highly effective electrical conductor, carrying minute electrical signals (like from a body) to receptors, then up to the shark’s brain, which can sense the exact center of the field. This is how a shark knows exactly where to strike once it’s within about a meter of prey.
What about that whole drop-of-blood-smelled-from-miles-away thing? Myth. Yes, sharks have an excellent sense of smell, heightened by their sensitive ability to detect currents (thanks to their lateral lines — movement sensors sort of like a super-sensitive version of our inner ear, only running down the sides of their body), but the chemical signal of a single drop of blood carried over miles of current is way too dilute even for sharks to detect. A rotting whale carcass, on the other hand, is not.
Despite the above, we still know next to nothing about shark behavior. The fact was mentioned in the Shark Week documentaries I saw, but not the reasons why. Most of what we know about other large animals — dolphins, whales — actually comes from their study in captivity. You can’t do that with sharks, Atema says, because they usually die when confined. Sadly, he adds, many aquariums routinely replace their sharks for this reason.
We also know very little about their brains. We know the rough neuroanatomy, and that it’s mostly comprised of the equivalent of our limbic system on down (say, our amygdala, hypothalamus, etc., on down to the deep brain areas, like the brain stem), and we know where the main nerves connect the brain and body. But at a deeper level? Not so much. The shark’s brain function is so poorly understood that Atema won’t even rule out that sharks have no other brain areas that might be functioning at a higher level than we give them credit for.
Shark Week has it right: sharks are here to stay on the Cape. As long as we protect one of their favorite foods (seals), sharks will stick around. “… in a way, it is an accident waiting to happen — people are swimming around the same areas as the seals. Great white sharks are not human hunters, but if they take a little bite and, oh sorry, I thought you were a seal, it’s still going to be too late for the human.” But, hey: don’t blame the shark; he’s just doing what he was meant to.