Researchers have gained insight into how sharks expertly sniff out their prey.
A research team looked at how "vision, touch, smell and other senses" combine to drive the sharks' behavior, a Mote Marine Laboratory news release reported.
The team found that the shark's lifestyle had a large effect on which senses they favored; they also found the sharks may have the ability to block certain senses.
The researchers hope these findings will help work towards the preservation of the dwindling shark species. Understanding shark senses could help researchers better-understand how factors such as pollution and overfishing could affect their behavior.
Past studies have shown that sharks use their sense of smell to sniff out prey from far away, and swim upstream towards the appetizing scent using their lateral lines (the touch-sensitive systems that feel water movement). Once the shark reaches its prey at a close distance it is believed to use its sense of vision to strike; it could also use lateral line or electroreception ("a special sense that sharks and related fish use to detect electric fields from living prey").
"Our findings may surprise a lot of people," Doctor Jayne Gardiner, lead author of the study, who is a Postdoctoral Fellow at Mote and whose doctoral thesis at USF included the current study, said in the news release. "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 observed how captive blacktip, bonnethead and nurse sharks blacktip, bonnethead and nurse sharks reacted to bait dangled at the opposite side of their tank to make their findings. They also tried the experiment after blocking certain sense, such as covering one of the shark's eyes and plugging its nostrils.
The team found that blacktips and bonnetheads were able to recognize prey when their nostrils were blocked, but nurse sharks were not able to recognize the prey. Nurse sharks often feed in the dark, which could explain their increased reliance on smell.
When both vision and lateral line were blocked, the blacktip and bonnethead sharks were not able to follow the scent trail to the prey, nurse sharks were able to.
When electroreception was blocked most of the sharks were not able to capture their prey, but some did open their mouth at the appropriate time.
"We 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," Doctor. Bob Hueter, Director of Mote's Center for Shark Research and co-author of the current study, said in the news release. "What we found was amazing, not only in how the various senses mesh together but also how one shark species can vary from another. Not all sharks behave alike."
"This is undoubtedly the most comprehensive multisensory study on any shark, skate or ray," Doctor Philip Motta, a USF professor who co-authored this study, said in the news release. "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."
