Sharks possess uncanny skill at tracking down prey, but it's unclear how the animals sense their surroundings so acutely. New studies suggest that a clear jelly under a shark's skin keeps the animal informed about minute changes in seawater temperature that may serve as signposts to feeding grounds.
Brandon R. Brown, a physicist at the University of San Francisco, set out to characterize this mysterious gel. The salty brew of glycoproteins fills hundreds of electrosensory canals, called ampullae, that connect skin pores to subsurface nerve cells in sharks, skates, and rays.
After collecting gel from black-tip reef sharks and white sharks that had recently died at aquariums, Brown placed each sample in