27 May 2010
Shark attack stats highlight risk of monochromatic Speedos
by Kate Melville
An analysis of shark attacks by researchers from the University of Florida (UF) has found that attacks are most likely to occur on a Sunday, in less than 6 feet of water, during a new moon and involve surfers wearing black and white bathing suits.
The analysis was conducted using statistics from attacks that occurred in Florida's Volusia County, dubbed the "Shark Attack Capital of the World," between 1956 and 2008. The researchers also spent a year observing people between Daytona Beach and New Smyrna Beach, said George Burgess, director of the International Shark Attack File at UF.
"It's basically an analysis of why, where and when in an area that traditionally has had more shark-human interactions than any other stretch of coastline in the world," Burgess said. "One of our students, Brittany Garner, essentially camped out there, counted the number of heads on the beach and took photographs."
While this 47-mile-long section of Central Florida's Atlantic coast leads in human-shark skirmishes, making up 21 percent of all global attacks between 1999 and 2008, most are "hit and run" incidents that seldom cause serious injury and no fatalities occurred.
"Calling them attacks is probably a misnomer because the consequences are usually no more severe than a dog bite," Burgess explained. "They're not the same kind of bites made by 10- to 20-foot-long white sharks that you have off the coast of California. Here we see a different style of attack, primarily perpetrated by smaller fish-eating sharks such as spinners and blacktips that are less than 6 to 7 feet long, which because of their size normally seek smaller prey."
There have been 231 shark attacks between the first one reported in 1956 in Volusia County and 2008. According to Burgess, human, shark and environmental factors combine to create a perfect storm of favorable conditions in Volusia County for attacks, particularly near Ponce Inlet between Daytona Beach and New Smyrna Beach.
The more people in the water the greater the chances they will encounter a shark, and New Smyrna Beach south of the inlet is a "hot spot" for surfers. "Hand splashing and feet kicking provoke sharks, which bite and release what they mistake for normal prey items in the turbid waters," Burgess noted.
Young white males were attacked most because they spend the most time in the water, Burgess said. Ninety percent of victims were male, 77 percent of 196 victims were between 11 and 30 years old and in the 171 cases where race was known, 98 percent were white.
Well over half of the 220 victims were bit on the leg, more than five times the number bit on the arms, the second highest body part to be injured. Surfers were the most frequent victims, making up 61 percent of the total. They tended to be bitten more in the early morning and late afternoon when waves were highest and they spend more time surfing.
"At the time of the attack, most of the surfers were sitting or holding onto the board waiting for a wave, which explains why most surf victims were bitten on the legs," Burgess said.
Human leisure habits led to the fewest number of human encounters on Wednesdays and the highest on Sundays, followed by Saturdays. The greatest number of attacks occurred during new moons, followed by full moons, the edges of the lunar extreme when the moon has its biggest pull on the tidal phase. "Probably the moon's phases influence the movements and reproductive patterns of fish, the shark's food source, just as they affect human behavior," Burgess explained.
Most incidents involved one bite, occurred in turbid, murky or muddy waters and were at the water's surface. More victims wore swimsuits that were black and white than any other color combination, followed by black and yellow, attesting to sharks' abilities to see contrast.
Source: University of Florida