June 22, 2009

The Great White Shark’s Criminal Mind

According to a new study to be published in an upcoming issue of the Journal of Zoology, great white sharks appear to have a "serial killer" hunting strategy as they stalk their victims while skulking in the distance, rather than at random as was previously believed.

Predatory behavior is one of the most intriguing interactions seen in nature, with sharks being one of the most ferocious and violent on Earth.

Until recently, the predation of sharks has been difficult to observe and therefore greatly mysterious. Now, researchers from the United States and Canada are using geographic profiling in order to follow the predatory interactions between white sharks and fur seals in South Africa.

Geographic profiling is a method of investigating criminals that analyzes the locations in a connected series of crimes to determine where the offender most likely resides.

They found that sharks have a specific anchor point or search base for hunting. Most large sharks would stake out about 100 yards south of where the seals were on the island shore. While the anchor point did not give the shark the best chance of intercepting the seal, it did provide a great balance between detecting pray and seizing it.

"Sharks are apex predators, so studies of shark hunting behavior are important for understanding their ecology and role in structuring marine communities," explained Neil Hammerschlag, Ph.D. candidate at the University of Miami's Rosenstiel School of Marine and Atmospheric Science and co-principal investigator of the study. "Our need for more knowledge of these fascinating animals has become critical because of recent drastic declines in their populations globally."

With unbelievable strength and acrobatic power, the shark stealthily ambushes unsuspecting seals by coming at them from below with such a great force that it propels the prey from the water. "They hunt solitary juvenile Cape fur seals when light levels are low, stalking them from near the ocean floor to remain undetected, before launching a vertical attack," Hammerschlag said.

Hammerschlag and his collaborators from the University of British Columbia and Texas State University gathered data on 340 natural predatory attacks by sharks on seals in False Bay. They were then able to observe natural predatory behavior by great white sharks because attacks happen at the water's surface, making them visible from a distance.

The researchers found that spatial patterns of the sharks' hunt at this site were strategic, and that smaller sharks had less defined search patterns and lower kill success rates than larger sharks.

This could mean that white sharks base their hunting strategy on experience, and learn to focus on locations that give them the best advantage in capturing prey.  It might also suggest that larger sharks beat out the smaller sharks for choice hunting areas. 

In addition to being used in law enforcement, geographic profiling has been useful in many diverse and surprising applications, including studies of the foraging behavior of bats and bumblebees, the spread of infectious diseases in Africa, and the structure of terrorist cells in the Middle East.


Image Caption: University of Miami's Neil Hammerschlag and collaborators from the University of British Columbia and Texas State University collected data on 340 natural predatory attacks by white sharks on Cape fur seals in False Bay, South Africa. They found that spatial patterns of shark predation were not random and that smaller sharks had more dispersed prey search patterns and lower kill success rates than larger sharks. Credit: Neil Hammerschlag


On the Net: