New study finds sharks can switch among multiple senses to hunt prey

skennedy@bradenton.comApril 3, 2014 

MANATEE -- A new study has found sharks have the ability to switch among multiple senses in order to hunt prey.

The comprehensive study showed how vision, touch, smell and other senses combine to guide a detailed series of shark behaviors, including some caught at Terra Ceia Bay.

The surprising results revealed different sharks species favor different senses when on the hunt and sometimes switch when preferred senses are blocked, the lead author said.

"They can go to an alternate sense," said Jayne Gardiner, a postdoctoral fellow at Sarasota's Mote Marine Laboratory.

The study tracked exactly how the various shark senses work together while hunting.

Three shark species -- blacktip, bonnethead and nurse -- were studied in a large, specially designed tank at Mote Marine Laboratory, where water flowed straight toward them.

Dangling a fish or shrimp at the opposite end of the tank, researchers released a hungry shark and tracked its movement toward prey.

Next, they temporarily blocked the shark senses one by one, and in combination, using eye coverings, nose plugs to block smell, antibiotics to interfere with lateral lines that detect water motion, and electrical-insulating materials to block elec

trosensory pores on their snouts.

Then they captured the action with high-speed video.

Gardiner said the most surprising aspect of the study "was the flexibility of the behavior use of sensory cues, the fact they were able to switch when the preferred senses became unavailable. They could switch to an alternate sense."

"We were surprised at that, that the behavior was so flexible," she said.

Another surprise was, contrary to common wisdom, it's not all about smell.

"We often talk about sharks as swimming noses ... all sorts of things about their incredible sense of smell, but not all sharks need smell to feed," Gardiner said. "A nurse shark relies on smell. It can locate a fish, but it won't eat the fish unless they can smell it. But the blacktip and the bonnethead did just fine without smell. They did it visually."

The findings are important because it means sharks can feed in a wider variety of environments, Gardiner said.

Although she could not estimate the cost of the study because it was part of a larger project, Gardiner said it was paid for with grants from the National Science Foundation and from the Porter Family Foundation, and using funds provided through a University of South Florida Presidential Doctoral Fellowship, along with various research awards and support from professional societies.

The study is undoubtedly the most comprehensive multi-sensory work on any shark, skate or ray, said co-author Philip Motta, a professor at the Tampa campus of USF.

"Perhaps the most revealing thing to me was the startling difference in how these different shark species utilize and switch between the various senses as they hunt and capture their prey," he said. "Most references to shark hunting overemphasize and oversimplify the use of one or two senses. This study reveals the complexity and differences that are related to the sharks' ecology and habitats."

Other researchers included Boston University's Jelle Atema and Robert Hueter, director of Mote Marine's Center for Shark Research.

Gardiner, 34, of St. Petersburg, holds a Ph.D. in biology.

She became interested in fish as a child growing up in Canada, where she went trout-fishing with her father and grandfather.

"I became interested in fish and behavior in animals in general," she said. "...there's still a lot we don't know about these animals. There's lots of room to study these things.

"I got hooked on them."

Sara Kennedy, Herald reporter, can be reached at 941-745-7031. Follow her on Twitter @sarawrites.

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