- Associated Press - Wednesday, April 2, 2014

SARASOTA, Fla. (AP) - What happens when you plug a shark’s nose? Will it still be a lethal killer without its legendary sense of smell?

The answer, surprisingly, is yes - at least in some shark species.

In a study published Wednesday in the journal Plos One, researchers used eye coverings to block sight, nose plugs to block smell, and insulating materials to cover the electrosensory pores on the sharks’ snouts. They took high-speed video of the impaired sharks and found that some can still find their prey even without smelling it.

The scientists - from the University of South Florida, Mote Marine Laboratory and Boston University - were trying to better understand how sharks use all of their senses when hunting for prey.

USF biology professor Philip Motta said that past research has focused on solely one sense, but the research that was released Wednesday shows how sharks can be flexible in the senses they use to track down prey.

“It’s really a multi-modal set of signals that guides the shark toward its prey,” he said. “They’re much more complex than we thought.”

Mote Marine researcher Jayne Gardiner said the team worked with three different Gulf of Mexico shark species - nurse, blacktip and bonnethead. They put the sharks in a specially outfitted tank at Mote’s Sarasota research facility, where the water flowed straight toward them. Then they dangled a prey fish in the water and released the shark.

They blocked different senses in each shark species. Along with eyes, nose and pores, the researchers used antibiotics to interfere with their so-called “lateral lines” - the touch-sensitive systems that allow the fish to feel water movement.

Each shark responded differently.

Nurse sharks didn’t recognize their prey if their noses were blocked, but the blacktips and bonnetheads did. When the scientists blocked vision and lateral lines, the blacktip and bonnethead sharks could not follow the odor trail to locate prey - but nurse sharks could. During normal feeding, the prey’s electric field triggered all of the sharks to opening their mouths at very close range. When researchers blocked the vision and lateral lines, the sharks didn’t strike, even when they were close enough to sense the prey’s electric field.

“It does tell us that they’re certainly motivated to feed, like many, many animals are,” said Gardiner. “But it tells us they’re very flexible in terms of which sensory cues that they’re using. It tells us that they’re adaptable to some changing conditions, as far as some available sensory information.”

Motta said the information will help researchers figure out how pollution and degraded marine environments affect sharks - say, if chemicals interfere with a shark’s sense of smell, for instance.

“When we disrupt habitats, it may have long term effects of the feeding behavior of these sharks,” he said.


Follow Tamara Lush on Twitter at https://twitter.com/tamaralush

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