By Dave Sigworth, publicist of The Maritime Aquarium
We know that sharks are cool. Every once in a while, we find out that they’re even cooler than we thought.
This week’s “reputation boost” came from researchers at the University of Western Australia, who described how baby sharks can detect a threat from predators even before they’re born.
Before the details, let’s back up for some background.
Backgrounder No. 1: The species of shark that was studied – brown-banded bamboo sharks – aren’t born. They hatch.
Bamboo sharks and many other species don’t have “live” births. Instead, the females deposit their embryos into the water within leathery egg cases. (Skates and rays – which are cousins to sharks – do this too.) If you’ve visited The Maritime Aquarium, you’ve encountered these empty egg cases at the Intertidal Touch Tank. They’re nicknamed “mermaid’s purses.”
The baby sharks develop in these egg cases and then hatch out. Prior to hatching, they’re vulnerable to fish, large mollusks and other predators.
Backgrounder No. 2: Sharks have a sort of sixth sense that lets them detect electrical impulses given off by living things. (That’s how they can “see” a flounder buried in the sand.) Receptors for this ability are visible as a series of tiny holes on the shark’s snout called the ampullae of Lorenzini.
Now, back to what the Australians found: According to news reports, the researchers discovered that “even within their egg cases, the embryos could apparently detect electric fields in the lab created to mimic those of predators, such as fish. Video recordings showed the developing shark babies responded by ceasing all movements of their gills and keeping their bodies perfectly still.”
They played dead. Clever baby sharks!
Visit The Maritime Aquarium’s Shark & Ray Gallery and you can see baby chain cat sharks developing in their egg cases. They’re backlit, to reveal the embryos inside. You can watch them wriggling and breathing. And, because they’re behind glass, they won’t detect you and play dead.