The truth about piranha attacks

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Piranhas aren't the man-eaters folklore would suggest; you're much more likely to lose a toe, according to the results of a new survey of piranha attacks in Suriname.

Humans are much more likely to be bitten when piranhas are removed from the water when fishing than they are while bathing in the water, the study claims.

"Many human deaths attributed to piranhas are probably cases of scavenging on drowned or otherwise already dead persons", says Jan Mol of the University of Suriname, who has just published the results of a study on human attacks by piranha.

"In 15 years of field work in Suriname, often wading for hours through 'piranha-infested' streams and catching piranhas with hook and line while bathing in the river, I was never injured by free-swimming piranhas.

"Piranhas are usually more dangerous out of the water than in it and most bites occur on shore or in boats when removing a piranha from a gillnet or hook, or when a 'loose' piranha is flopping about and snapping its jaws."

Other studies have come to similar conclusions, but Mol suggests that under some situations the risk of piranha attack is very real.

"In the low-water season, when hungry fishes become concentrated in pools, some piranha species may be dangerous to any animal or human that enters the water."

Serrasalmus rhombeusMol studied Serrasalmus rhombeus attacks at three locations in Suriname; the villages of Donderkamp and Corneiskondre on the Wayombo River and a recreation park at Overbridge on the Suriname River.

Dozens of people had been attacked at each location, with most injuries resulting in bites to the heel, soles of the feet and toes.

More serious deeper wounds were also inflicted to the legs, arms and body. Some bites were so severe that the fish completely removed the toes, including the phalange bone.

Reader Mike Rizzo suffered this bite from his rhombeus last year. Full story

The recovery of toe phalanges, complete with human flesh and bits of toenail, identified the culprits as Serrasalmus rhombeus, one of the largest and most aggressive piranhas.

"Individuals of this species tend to remain several weeks at one site and this may explain why the respective piranhas were caught at exactly the same spot after their attacks on bathers", says Mol.

"Also, characteristics of wounds of victims from Overbridge resembled bite marks previously documented as caused by S. rhombeus. Furthermore, no Surinamese freshwater fish other than a piranha could be responsible for the injuries reported here."

None of the three locations surveyed had reported any human deaths due to piranha attacks.

Two epileptic bathers whose badly mutilated bodies were retrieved from the water are believed to have suffered seizures and then been scavenged by the fish.

Villagers interviewed by Mol claimed that piranha attacks in the small villages were unheard of until the population of the village began to rise in 1990.

When the human population peaked, the number of piranha attacks increased.

Feeding, not defenceWhile piranha attacks in other areas have been attributed to attacks by breeding piranhas defending their eggs and fry, Mol believes this is not the case in Suriname.

"In Surinamese rivers most of the reproductive activity of S. rhombeus occurred in the long rainy season of April to July, while most piranha attacks in Overbridge and Donderkamp occurred during the low-water (dry) season of September to November.

"Nevertheless, there is a small possibility that some individual piranhas were reproducing and guarding their spawn and/or spawning sites out of the main season."

The sites not only lacked stereotypical spawning sites for the species, but the surveys revealed only sexually immature juvenile piranhas, so Mol believes that the attacks stem from feeding behaviour, not the defence of offspring.

How to avoid being eaten1. Piranhas are only found in certain rivers in the Amazon basin. Avoid swimming in South America, unless you have to. If you must bathe there, fill a bucket and wash on land. But look out for Centromochus!

2. Piranha attacks are greatest during the dry season when water levels are lowest and the fish breed, resulting in thousands of hungry young piranhas in the water.

3. Human attacks are most common in areas where human densities are highest in the water, such as popular swimming spots.

4. Noise and splashing attracts piranhas, so try to avoid making a commotion while you're taking a dip. Piranha most commonly attack children for this reason.

5. If you're a menstruating woman, don't swim in the water, as any leaking blood may attract piranhas. In Amerindian villages, women in menstruation are not allowed to bathe for this reason, says Mol.

6. Don't throw dead fish, offal or other food into the water. Piranhas are not strictly carnivorous, so any food in the water might attract them into the area.

7. Piranha attacks are not isolated incidents. If you spot any signs erected by locals saying "Warning Piranhas", it's probably sensible to avoid bathing there.

For more information see the paper: Mol JH (2006) - Attacks on humans by the piranha Serrasalmus rhombeus in Suriname. Studies on Neotropical Fauna and Environment, December 2006; 41(3): 189-195.