isquiotibiales

Sarasota - How sharks hunt prey — from the first whiff to the final chomp — will be revealed as never before in a new study about shark senses that was supported by the National Science Foundation and will be published March 27 in the peer-reviewed journal PLOS ONE.
The study, led by scientists from Mote Marine Laboratory, the University of South Florida (USF) in Tampa and Boston University, is the first to show how vision, touch, smell and other senses combine to guide a detailed series of animal behaviors from start to finish.

Results show that sharks with different lifestyles may favor different senses, and they can sometimes switch when their preferred senses are blocked. That's hopeful news for sharks trying to find food in changing, sometimes degraded environments.

Understanding how sharks sense and interact with their environment is vital for sustaining populations of these marine predators, which support the health of oceans around the world. Overfishing is the greatest known threat, but pollution and other environmental changes may affect the natural signals that sharks need for hunting and other key behaviors. In addition, understanding the senses of sharks and other marine life could inspire new designs for underwater robotics. However, before shark senses can teach us anything, scientists must gain a basic understanding of how they work.

Past studies have suggested that sharks sense the drifting smell of distant prey, swim upstream toward it using their lateral lines — the touch-sensitive systems that feel water movement — and then at closer ranges they seem to aim and strike using vision, lateral line or electroreception — a special sense that sharks and related fish use to detect electric fields from living prey. However, no study has shown how these senses work together in every step of hunting, until now.

"Our findings may surprise a lot of people," said Dr. Jayne Gardiner, lead author of the study, who is a Postdoctoral Fellow at Mote and whose doctoral thesis at USF included the current study. "The general public often hears that sharks are all about the smell of prey, that they're like big swimming noses. In the scientific community it has been suggested that some sharks, like blacktips, are strongly visual feeders. But in this study, what impressed us most was not one particular sense, but the sharks' ability to switch between multiple senses and the flexibility of their behavior."


The researchers placed blacktip, bonnethead and nurse sharks — three species found along Florida's coast that differ in body structure, hunting strategy and habitat — into a large, specially designed tank where the water flowed straight toward them. The researchers dangled a prey fish or shrimp at the opposite end of the tank, released a hungry shark and tracked the shark's movements towards the prey.

Next, they made the hunt more challenging: They temporarily blocked the sharks' senses one by one using eye coverings, nose plugs to block smell, antibiotics to interfere with their lateral lines that detect water motion and electrically insulating materials to cover the electrosensory pores on their snouts.

Then the researchers took high-speed video — lots of it. "We had hundreds of video clips to sort through, and we had to get just the right angle to see when the shark was capturing the prey," Gardiner said.