the shocking truth about Piranhas
In the languid news week after Christmas, hungry media outlets swarmed over a report of piranhas attacking swimmers on a river in Argentina. “Massive Piranha Attack” cried The New York Post. “70 Christmas Day Bathers Are Savaged” added The Daily Mail, promising “the truth about the fish with a bite more powerful than a T. rex.” ABC News called it a “Christmas Day feeding frenzy.” In fact, the injuries ranged from minor cuts to at least one missing finger part — not exactly as newsworthy as, say, the 800,000 Americans who require medical treatment for dog bites each year.
Piranhas have always been among our favorite subjects for sheer, sputtering nonsense. Theodore Roosevelt, on a 1913 expedition in South America, called piranhas “the most ferocious fish in the world.” More recently, multiple “Piranha” movies have ridden this hysteria to the bank.
This is an awful lot of hype for piranhas to live up to, and predictably, they disappoint. To test the colorful mythology of the ferocious piranha, I once climbed into a tank of hungry red-bellied piranhas at the Dallas World Aquarium. (They fled to the opposite corner.) In the Peruvian Amazon, I stood waist-deep in the Rio Napo while catching and releasing piranhas on a hook-and-line. (The nibbles were strictly of the usual kind.) In the flooded grasslands of Venezuela, I drove around tossing a chicken carcass into various bodies of water to time how long it took for the flesh-maddened swarms to strip it to feathers. (There was enough chicken left at the end of the day to feed a family of four.)
The point of this exercise, recounted in my book “Swimming With Piranhas at Feeding Time,” was that piranhas do that swarming, blood-crazed, flesh-ripping thing only in a couple of rare circumstances, both involving a highly concentrated food source: They will swarm around bird rookeries, where the fledglings leaving the nest often tumble straight down into the water. And they’ll do it around docks where fishermen clean their catch and heave the guts into the water.
Otherwise, you can swim without fear.
I didn’t worry about piranhas, for instance, when the only place to bathe, on a recent trip deep into the backcountry of Suriname, was the river running past our camp.
Then one day, sitting in a canoe, I watched the fish biologist on our expedition, Jan H. Mol of the University of Suriname, pull a 12-inch-long black piranha out of the same water where we took our daily baths. As this extremely toothy creature wriggled in his hands, Mr. Mol started talking, in his somewhat ponderous way, about a paper he had published on piranha-bite incidents, complete with color photos of amputated toes.
Like me, Mr. Mol believes the piranha threat is wildly exaggerated. He has spent more than 20 years wading in South American rivers and hauling up every imaginable fish without ever being injured by free-swimming piranhas. “Free-swimming” is, however, the operative phrase there: If you get careless while trying to untangle one from a net, or you let one flop around the bottom of the boat, things can get painful.
As he spoke, Mr. Mol was using the soft pad of his index finger to hold down the piranha’s sharply serrated lower jaw and give me a better view. It was a formidable mouthful. But that index finger rather spoiled the effect of another recent study, in the journal Nature, which found that the black piranha’s bite is more powerful, pound for pound, than that of a great white shark or a killer whale. Yes, yes, that article also mentioned T. rex, but “pound for pound” (or as the authors put it, “removing the effects of body size”) turns out to be another of those pesky operative phrases.
We chatted briefly about the classic studies by the Brazilian researcher Ivan Sazima, who observed piranhas in the clear-water ponds and creeks of South America’s vast Pantanal wetlands. Mr. Sazima found that these generally timid little fish mainly feed by nipping off fins and scales from passing fish, not by ripping their flesh. Mr. Sazima is also an author of a paper with the lovely title “Scavenging on human corpses as a source for stories about man-eating piranhas.” It concluded that when human bodies turn up in the water with signs of piranha attack, it’s almost certainly because the piranhas were scavenging on people who were already dead.
Even piranha specialists would struggle to come up with a dozen cases over the past half-century in which multiple living human victims were injured. In the two cases Mr. Mol investigated in northwestern Suriname, one in the 1950s and the other in the early 2000s, most of the victims suffered a single relatively minor bite on the feet or legs. He found that in each case, there was a factor that attracted piranhas to the area — fishermen gutting their catch nearby or holiday visitors spilling food in the river. Mr. Mol theorized that the piranhas bit humans by accident at first, and then, recognizing a newly abundant food source, began to take advantage of it. Other fish specialists I spoke to or emailed the other day argued that those incidents, and the more recent one in Rosario, Argentina, were all cases of defensive biting.
Christmas Day was unusually hot in Rosario — about 100 degrees Fahrenheit — and people were crowding into the river. It’s also mating season for the three local piranha species. It’s likely, said Prosanta Chakrabarty, a fish biologist at Louisiana State University, that bathers inadvertently wandered into male breeding territories, provoking a brief but hostile response.
None of the attacks escalated into a classic piranha swarm. It wasn’t, as The Daily Mail reported, “like a scene from a horror film” with swimmers being “savaged by shoals of the razor-toothed fish,” which ripped away “chunks of their naked and exposed flesh.” Victims were able to walk back to the beach without being attacked by other piranhas. Other beachgoers were back in the water a half-hour later.
So what’s the bottom line on piranhas? “If something is potentially dangerous to humans, it will be dangerous in certain conditions,” Mr. Mol told me, as we sat in the canoe that day in Suriname. But those conditions are extremely rare, and the danger tends to be highly limited.
We ate the piranha for dinner that night, and I continued to bathe in the river.
But — this is the thing about human nature — now and then I also paused to count my toes.
Richard Conniff is the author of “The Species Seekers: Heroes, Fools, and the Mad Pursuit of Life on Earth.”
A version of this article appears in print on Jan. 5, 2014, Section SR, Page 5 of the New York edition with the headline: Shocking Truth About Piranhas Revealed!.
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In the languid news week after Christmas, hung first appeared on My Blog.
