MELBOURNE, Fla. — They rarely get cancer. Their wounds heal much faster than humans'. Their unique skin makes for a low-drag glide through the water that engineers envy. Scientists say sharks have much to teach us: from how we treat illnesses to how to make better ships, undersea robots or even swim suits.
But despite the huge popularity of sharks as research subjects, the wonders of their physiology and behavior remain mostly a mystery.
Among the more notable "holy grails" of ongoing shark inquiry:
• Ship building. Boat makers marvel at how sharks have incredibly low drag relative to other fish, a hydrodynamics enabled by scales that resemble tiny backwards-pointing shark teeth. Something in their skin mucus also keeps sharks free of barnacles and other so-called "biofouling." Shipbuilders hope to mimic similar engineering and "anti-fouling" feats so fleets can save on fuel.
• Neuroscience. Researchers are studying shark brains to see what they could teach us about human brains or about improving how undersea robots navigate. Could brain implants in sharks one day enable the military to remotely control sharks or train them to secretly track enemy vessels? The Defense Advanced Research Project Agency funded experiments attempting such tactics in 2006. Scientists say it went nowhere, but similar research into how sharks navigate continues.
• Cures. Could sharks harbor compounds with essential clues for curing cancer, other diseases, or rapidly healing human wounds — infection free? Maybe what we learn from the awesome immunity of sharks could one day save millions of lives.
"Within hours after a wound is opened up on a shark's body, a coating of cells begins to grow over, faster than anything that mammals do," said Bob Hueter, director for the Center for Shark Research at Mote Marine Laboratory in Sarasota.
That cell coating is complete within a day.
"The immune cells of sharks and rays also create substances that selectively kill human tumor cells in culture," he said.
Some research at Mote, funded by the U.S. Department of Defense, aims to tap that healing ability to develop better antibiotics. Compounds in the mucus layer of rays and sharks might yield new medicines to heal wounds on the battlefield and elsewhere.
Researchers at Florida Institute of Technology also want to unlock the secrets of shark "slime."
Nothing much seems to stick to sharks. Properties of their skin give them a slick, clean, low-drag glide through the water that makes shipbuilders envious.
Kaikea Nakachi, a senior at FIT pursuing a degree in biological oceanography, is studying why barnacles and other tiny marine crustaceans don't cling to sharks.
For his summer senior field project at FIT, he wanted to do something with sharks. FIT associate professor Kevin Johnson, who focuses on invertebrate planktonic larvae, had a thought: Could shark slime yield better ship hull coatings?
"Think barnacles on a boat," explained Johnson, a biologist at FIT's Marine and Environmental Systems Applied Research Laboratory. "There's a huge industry in anti-fouling."
Maybe the chemical properties of shark slime discourage biological growth and could yield similar, environmentally friendly substances that could be added to marine paints to prevent barnacles and other miniature marine life from clinging to ship hulls.
But there's more to sharks' clean, smooth glide than slime.
Decoding the physics of shark skin could, in a way, help win wars, or fight climate change by teaching engineers more fuel-efficient designs for ships, reducing the carbon footprints of military and commercial fleets.
Sharks' tiny, razor-sharp scales, called denticles, are formed from the same embryonic tissue as their teeth. The scales point toward the tail, so if you rub a shark from nose to tail, it's smooth, and from tail to nose, it's like sandpaper.
The scales alter waterflow over the shark's skin in a way that's been likened to dimples on a golf ball and that helps generate thrust when the shark moves.
Boat and swimsuit makers want to emulate that.
Using 3-D printing, scientists at Harvard recently fabricated the first faux shark skin and calculated its hydrodynamic benefits. They used sophisticated computer imaging to scan skin from a mako shark.
Manufacturing materials that can mimic shark skin could yield more hydrodynamic boats, swimsuits and aircraft designs.
But the most uncanny shark trait is its sensory perception.
Their ability to smell, feel or otherwise home in on targets from afar stands unparalleled at sea.
Using a series of sensory pores in their snouts — called ampullae of Lorenzini — sharks can sense extremely weak electric fields, as small as 1 millionth of a volt per centimeter of seawater.
A 2007 Scientific American article likened this to sensing the field created by a 1.5-volt AA battery, with one pole dipped in waters off Jacksonville and the other into the Long Island Sound. A shark swimming between the two could, in theory, easily sense whether the battery was on or off.
Sharks can sense the electric activity that moves muscles and makes hearts beat in prey.
Theoretically, once scientists figure out what makes sharks' minds tick, they could mimic certain stimuli to control them.
In 2006, research funded by DARPA put neural implants in sharks brains to learn more about how they navigate to their targets.
The idea was to stimulate the parts of the brain triggered by the odor plumes that sharks sense from their usual prey, turning the shark left or right at will.
"It was kind of hush-hush work," said Hueter, of Mote Marine.
Mote conducted similar research in the 1960s and early 1970s for the Office of Naval Research, Hueter said, exploring the possible use of sharks for military applications. The work was classified, he said.
The brain implants in the DARPA-funded study failed, said Jelle Atema, a biology professor at Boston University, who studies sharks at Woods Hole Oceanographic Institution. The moment the shark would wake up from anesthesia from the surgery, its brain would move in its skull, breaking contact with the electrodes, Atema said.
But beyond undersea espionage, there are plenty of other ways sharks can help humanity.
"I think the most important thing for us is just basic biology," Atema said. "We would really like to know what the shark knows about its environment and how it knows that information."
Understanding how sharks find their way around could improve navigation for Autonomous Underwater Vehicles, which could be programmed to use the same sort of sensory cues to locate targets.
Watching where sharks go might even lead to better hurricane forecasts.
Researchers at University of Miami are tracking sharks via satellite to see if their warm-water travels can help improve hurricane intensity forecasts, by providing more information about ocean temperature.
The list of what sharks can show us seems endless, with much more to come.
"We'd like to know — what can the shark really do," Atema said.
