The remarkably clever dolphin has amused us with its tricks and intrigued us with its intelligence, and now it turns out that it routinely defies death. It can ignore a wound that would kill a human within hours. Dolphins, according to a new study, are frequently attacked by sharks that leave gaping holes bigger than a basketball.
"Why don't they bleed to death?" asks Michael Zasloff, professor of surgery and immunology at Georgetown University Medical Center. "Why don't they get infections? Why aren't they eaten after the injury? Why doesn't the shark finish the job?"
Zasloff thinks he may have at least partial answers to those questions, although much more research needs to be done.
"I have concluded that what we see when we look at the dolphin is a medical miracle," he said in a telephone interview. And if scientists can figure out exactly how the dolphin cheats death, maybe humans can eventually learn how to do it too, through better treatment of all sorts of injuries, not just shark bites.
Zasloff is a surgeon, not a dolphin expert, but his interest in this sea-going mammal began nine years ago when he was visiting a marine lab in Scotland. He was told that 70 to 80 percent of the dolphins that swim in the waters near Australia have shark bites.
"When I heard that I was taken aback," he said. "How in the heck does a mammal, like you and me, survive a shark bite in the ocean, unattended, with no antibiotics?"
A shark bite involves more than just ripping out a large chunk of flesh. The shark leaves "the worst collection of toxic organisms" in the wound, so infection should follow. A human being would die of infection and shock within two or three days if not hospitalized. So how does a dolphin heal itself without medical treatment?
That question haunted Zasloff for nine years, but a few months ago, he began working with Australians who are in constant contact with bottlenose dolphins, including Trevor Hassard, director of the Tangalooma Wild Dolphin Resort on Moreton Island. The resort is different from most aquatic parks in that the dolphins are free to visit, where they get an easy meal, or leave and return to the wild whenever they so desire.
No Obvious Pain, and No Scars
Over the years Hassard and others who care for wild dolphins have seen hundreds of dolphins that have been attacked by sharks. If the attack was recent, an open wound, usually on the backside of the dolphin, seemed to have little effect on the animal. It swam normally, did not show any sign of pain -- though dolphins clearly can experience pain -- and acted as though nothing was wrong. And within about 30 days the wound was gone. There were no scars. No signs of the injury. Even the natural contour of the body was back to its normal shape.
So the dolphin doesn't just recover from the attack. It regenerates the blubber and refills the hole.
"That's impossible," Zasloff said. "It's truly impossible."
How could it regenerate the blubber - which is actually a complex matrix of fibers, not just fat -- to heal itself?
Zasloff theorizes -- and this is just theory at this point -- that the injured dolphin can produce stem cells that can morph into whatever is needed to fill in the wound. Perhaps, he speculated, it has some sort of a growth hormone that stimulates the production of stem cells, and maybe that same hormone would work for other mammals, including humans. A lab with access to injured dolphins should be able to isolate the hormone, if it's there, he said.
During that month-long healing process, the dolphin is exposed to all sorts of pathogens that should cause potentially fatal infections, but that doesn't happen. Zasloff has a theory about that, too, but it seems incredible. Perhaps, he suggested, the dolphin carries its own packet of antibiotics.
There is a lot of research on the composition of the blubber, and it includes "compounds that look a lot like the antibiotics that other sea creatures have to protect themselves," like algae and plankton, Zasloff said.
Maybe when the dolphin consumes those other creatures, it doesn't metabolize the natural "antibiotics" and return them to the sea. It could be that it stores those vital compounds and deploys them to an injury inflicted by a shark.
"It's not breaking them down," Zasloff said. "It's storing them in the blubber. It's as if the dolphin has decided to keep the good stuff that is made in the ocean by other creatures to fight bacteria."
But what about the pain? The Australian caregivers say dolphins attacked by sharks don't act as if they are in pain at all.
"The animal will have a gaping wound in its back, and yet it shows no evidence of any change in behavior," Zasloff said. "The animal doesn't look disturbed. It is eating as though nothing happened. That's what amazed Hassard initially."
He suspects the animal not only carries antibiotics -- it also comes equipped with built-in painkiller.
"I propose that the wound itself is releasing a pain-relieving substance, and it must be unbelievably powerful. It has to be activated at the site of the wound, and it is not going to be addictive. I would say that is perhaps the most miraculous of all," he said.
It carries its own anesthesia?
"I would call it morphine," he added. "I think we'll find it in the tissue."
But that leaves us with a final question. Why didn't the animal bleed to death in the minutes after the attack?
"That's the easy one," Zasloff said.
The dolphin probably goes into a deep dive right after the initial attack in an effort to escape, and during the dive it will need all its available blood to pump oxygen to the brain. So it shuts off the blood flow to much of the rest of its body, including the wound. By the time the animal surfaces -- maybe 20 minutes or so later -- the small amount of blood in the wound would have coagulated, closing down any possible bleeding.
Zasloff published his findings in the Journal of Investigative Dermatology, and although he says he is not a dolphin expert, he has consulted others who are. Brent Whitaker, deputy executive director for biological programs at the National Aquarium in Baltimore, described Zasloff's work as "thought provoking." Leigh Ann Clayton, director of the department of animal health at the aquarium, called his proposals "fascinating."
It will be a while before we know if he's right. If so, the dolphin is much more fascinating that we ever imagined.