Linda Geddes, New Scientist 22 Jun 09;
Great white sharks have more in common with serial killers than just their fearsome reputation. It turns out that their hunting strategies are far from random. When deciding where to launch their attacks, they balance prey availability with factors such as finding a good hiding place – just serial killers do.
Little was know about great whites' hunting strategies, except that they are more successful at hunting in low light conditions, and that large sharks tend to be better a catching prey than smaller younger sharks. So Neil Hammerschlag of the University of Miami, Florida, and his colleagues used geographical profiling, a tool more commonly used by police tracking down serial killers.
To investigate how sharks hunt for Cape fur seals off Seal Island in South Africa, the team used the locations of 340 shark attacks to determine whether the sites of such attacks were random, and if not, the most likely "anchor point" from which attacks were being launched.
When the team fed their results into computer model, it suggested that great whites don't attack at random, but from well-defined anchor points or lairs.
"This wasn't where the seal concentration was greatest," says Hammerschlag. He suspects it was a balance between prey detection, competition with other sharks, and environmental conditions that let them launch a quick vertical attack where the water is clear enough to see the seals.
Larger, older sharks also seemed to have more defined anchor points than younger sharks. "This could mean two things. Sharks could refine their hunting with experience. It could be that as they get older, the sharks learn which are the best hunting spots," says Hammerschlag. Alternatively, the larger sharks could be deliberately excluding the smaller sharks from the best hunting spots, leaving them to take their chances elsewhere.
Journal reference: Journal of Zoology (DOI: 10.1111/j.1469-7998.2009.00586.x)
