Study Shows Sharks Combine All Their Senses to Hunt
A first-of-its-kind study of how sharks hunt has found the long-feared fish are truly complete predators, using all of their senses in an array of different combinations and ways.
Findings from the work, which was supported by the National Science Foundation, were published in the peer-reviewed journal PLOS ONE.
Led by scientists from Mote Marine Laboratory in Sarasota, Fla., the University of South Florida in Tampa and Boston University, the research sought to better understand how a shark's vision, touch, smell and other senses seem to combine and guide a detailed series of behaviors from start to finish.
Basically, the results demonstrate that sharks with different lifestyles may favor different senses, but can sometimes switch which ones they use when their preferred senses are blocked.
The researchers explained in a news release that knowing how sharks sense and interact with their environments is critical in trying to sustain the populations of predators, which are in turn vital to the health of the globe's oceans.
Past research suggested sharks sense the drifting smell of distant prey, swim toward it using their lateral lines, sensors that feel water movement, and then at closer ranges aim and strike using their vision, lateral line or electroreception -- another ability that allows sharks and related fish to detect the electric fields produced by living prey.
No study before, though, set out to show how these senses work together throughout the hunting process, until now.
"Our findings may surprise a lot of people," said Jayne Gardiner, lead author of the study and a postdoctoral fellow at Mote, whose doctoral thesis 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 -- all three of which are found along Florida's coast but 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. They next made the hunt more challenging by blocking the sharks' senses one by one, first with eye coverings, then nose plugs, followed by antibiotics to interfere with their lateral lines that detect water motion and finally employing electrical insulating materials to cover the electrosensory pores on the fishes' snouts.
"This is landmark work," said co-author Jelle Atema, a professor of biology at Boston University and an adjunct scientist at Woods Hole Oceanographic Institution. "Back in 1985, world experts in underwater animal senses met at Mote, and at that time we emphasized that sensory studies were focusing on one animal at a time, one sense at a time, and we needed to start combining this information. Now we have."
Undoubtedly, asserted Philip Motta, a USF professor an study co-author, the researchers ended up with "the most comprehensive multisensory study on any shark, skate or ray ... 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. 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."
The research team "sought to discover how sharks use their highly evolved senses to hunt and locate prey, knowing it involved more than just a good sense of smell," said Bob Hueter, director of Mote's Center for Shark Research and another study co-author. "This also could help explain why most shark 'repellents' may work for a short time but are eventually overcome by persistent sharks."
Said Hueter: "What we found was amazing."