Sharks Use Several Senses to Track Prey

Sharks employ multiple senses while tracking a prey, a new study has found. The research shows that the fish can switch between its senses and doesn't rely only on its legendary sense of smell.

The study, by researchers at Mote Marine Laboratory and colleagues, was based on an experiment conducted on blacktip, bonnethead and nurse sharks. These sharks were placed in a large, specially designed tank. Researchers controlled water movements and placed a prey in the tank. The team then monitored shark movements using several cameras.

Sharks are known to have lateral lines, which are the touch-sensitive systems that detect movement in water.  Past research has shown that sharks smell their prey and then follow it using lateral lines. At close range sharks can even use electroreception to track prey.

The team wanted to see whether blocking vision, smell or electroreception affected sharks' hunting ability. Researchers found that each species of shark responded differently.

Blacktips and bonnetheads were able to detect prey even when their noses were blocked while nurse sharks could not. But, nurse sharks could hunt even when they couldn't see the prey. According to the researchers, the three species of shark hunt in different environments, which could explain why one species needed vision to hunt while another needed smell.

When researchers in the current study blocked sharks' vision and lateral lines, nurse sharks could still find the prey while blacktip and bonnethead sharks could not track the prey using only odor. According to the researchers, nurse sharks often touch the bottom with their pectoral fins, which might have helped them sense the direction.

A failed electroreception system prevented all three species from catching their prey. However, blacktip and nurse sharks sometimes opened their jaws at the right instant when the prey touched their nose, according to a news release.

"This is undoubtedly the most comprehensive multisensory study on any shark, skate or ray," said Dr. Philip Motta, a USF professor who co-authored this study. "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 study was supported by the National Science Foundation and was published in the peer-reviewed journal PLOS ONE.

The study results show that sharks rely on several senses to hunt, meaning that the high level of pollution in the oceans might be limiting their ability to catch a prey. The findings could also help engineers design underwater robots that mimic sharks' movements to locate objects.