Imagine swimming in crystalline ocean waters shot through with sunlight when one of Earth's most notorious predators swims into view — a very close view.
Such pulse-quickening encounters are, in fact, the whole point for visitors to Tiger Beach, an idyllic spot in the Bahamas where eco-tourists can get up close and personal with tiger sharks — indiscriminate eaters known to devour everything from sea turtles to kegs of nails (and occasionally a few unlucky humans).
Yet it is by playing to the sharks' voracious appetites that dive operators are able to lure them into view, courtesy of generous offerings of chum — minced fish.
However, some have argued that the free meals — and resulting close encounters between humans and sharks — could have bad consequences for both species.
"People are concerned that it could be causing sharks to associate people with food," said shark researcher Neil Hammerschlag, an assistant professor at the University of Miami. Some worry that, like cartoon castaways eyeing each other hungrily in a boat, tiger sharks might, essentially, begin to see humans as giant pork chops with legs.
"Shark attacks are so very rare, so it's really hard to draw conclusions," Hammerschlag told OurAmazingPlanet.
Another concern, he said, and one that is easier to test, is that all the free food might disrupt the sharks' natural wanderings, and artificially limit their movements to areas close to tourist sites. (Why go hunting out at sea when the bipeds regularly serve up snacks?)
Since sharks are apex predators — a bit like the Godfathers of the ecosystem — and keep potentially disruptive ecological usurpers in check, such a change could have negative effects.
"They help keep balance," Hammerschlag said, "so if this really changes their behavior long term, it could have ecological consequences."
Neither idea has been properly tested, he said. To that end, Hammerschlag, heading up a team of researchers, designed a study to investigate.
They used satellite tags attached to the sharks' dorsal fins to track tiger sharks in areas where eco-tourism packages offer plenty of free food to the sharks — the Bahamas' Tiger Beach — and an area where the practice is forbidden — Florida.
All told, they tracked 11 Floridian tiger sharks and 10 Bahamian sharks, in near-real time, for spans of six months to almost a year. Hammerschlag said he expected the Bahamian sharks, with access to cushy meals, to travel far less than their Floridian counterparts.
"But, in fact, we found the opposite," he said. The Florida tiger sharks traveled, at most, 620 miles (1,000 kilometers) from their tagging site.
In contrast, "the tiger sharks from the Bahamas diving site moved massive distances," Hammerschlag said. "Definitely that area was important, but they didn't rely on it."
Some swam as far as 2,175 miles (3,500 km) out into the middle of the Atlantic and spent seven months there. The researchers noted that the difference could be related to size: The Bahamian sharks are bigger, and bigger animals tend to travel larger distances.
Their research is published today (March 9) in the journal Functional Ecology.
Hammerschlag said that the work indicates that eco-tourism, when done right, may not be all bad for sharks — crucial predators that are disappearing from oceans around the world, many falling victim to the lucrative and devastating shark-fin trade.
With proper policies, he suggested, people could continue to see economic benefit from sharks, but in a way that keeps the animals alive.
"In the Bahamas, they've encouraged shark diving because it's good for the economy, and because of that they're protecting sharks in their water," he said — something that Florida policymakers might want to keep in mind.
"I would say that before we ban these things outright, we should do some research," he said. "Rather than basing our decisions on fear, we should base them on fact."
Reach Andrea Mustain at email@example.com. Follow her on Twitter @AndreaMustain. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.