Great white sharks don't just cruise the ocean and happen across some seals, they have a clever plan of attack.
Credit: Neil Hammerschlag
BRISBANE: Using a tool developed to investigate serial killers, researchers found that great white sharks don't search for prey randomly - they have an 'anchor point' from which they launch attacks.
Seal-hunting sharks in False Bay, South Africa, consistently launch their attacks from an area that balances prey density, water clarity and depth, according to a report published last week in the Journal of Zoology.
"Sharks are not mindless killers, but use sophisticated hunting strategies," said study co-author Neil Hammerschlag, an ecologist at the University of Miami.
"Not mindless killers"
Although it's usually difficult to study marine predation in the wild, researchers were able to document the precise location, water depth and success of 340 attacks in a single winter because of the sharks' unusual attack method.
The sharks at False Bay stalk young seals by keeping to the ocean floor, where the seals can't detect them, before launching a strike from below that propels shark and seal out of the water vertically.
These highly visible attacks often happened so close to the researchers' boats that they could also estimate the size of the sharks.
Inspired by CSI
The researchers analysed their data with geographic profiling, a tool co-author Aidan Martin first read about in a CSI novel, Hammerschlag said.
Once a series of crimes is linked to a single offender, criminal investigators use geographic profiling to analyse the location of the crimes. This often identifies the 'anchor point' from which a criminal launches their attacks, usually their home or workplace.
Hammerschlag and his colleagues used geographic profiling to show that the sharks had an anchor point 100 m south of the place where the seals entered and left the water, a rocky outcrop called the launch pad.
Hammerschlag think that the anchor point represents the optimum balance between proximity to the launch pad, water visibility and dept. The seals are not too spread out, but the water is clear and deep enough for the preferred vertical attacks.
Although apex predators such as great white sharks are thought to have an important role in regulating marine ecosystems, their hunting strategies are little understood, Hammerschlag said. Geographic profiling could help shark conservation efforts by identifying critical hunting and feeding areas to protect.
Iain Field, a marine ecologist at Charles Darwin University in Alice Springs, Australia, said that although the use of geographic profiling in ecology was an interesting concept, its usefulness might be limited by the need to physically see the organisms involved. "It's a pretty cool idea, but I'm not sure it's applicable to other marine species," he told Cosmos Online.
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