April 7, 2014
A Collage Of Senses Help Sharks Hunt For Food: Study
[ Watch the Video: Sharks Sense Prey In Surprising Way ]
Brett Smith for redOrbit.com - Your Universe OnlineSharks are highly-evolved killing machines and a new study published in the open-access journal PLOS ONE has compiled a comprehensive picture of how these marine predators hunt – from start to finish.
The study portrays the collage of senses used by sharks to detect, track and strike their prey with ruthless efficiency. The research team – from the University of South Florida, Mote Marine Laboratory and Boston University – discovered that different sharks favor different senses and sharks often switch from relying on one sense to another if the situation calls for it.
“This is undoubtedly the most comprehensive multi-sensory study on any shark, skate or ray,” said study author Philip Motta, a USF biology professor.
“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,” Motta continued. “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 team noted that the sharks’ capacity to adapt to changing circumstances is a positive sign during this time of global climate change. While overfishing is the best known threat to sharks, marine pollution and other ecological transformations may affect environment that sharks assess for hunting and other necessary behaviors.
Past research has indicated that sharks sense the drifting scent of faraway prey, swim up-current toward it using tactile systems called lateral lines sense – which feels water movement – and then aim and strike using vision, lateral line or electroreception – another sense that some fish use to find electric fields surrounding living prey.
“The general public often hears that sharks are all about the smell of prey, that they’re like big swimming noses,” said study author Jayne Gardiner, a post-doctoral researcher at Mote. “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.”
To understand the hunting behavior of sharks, the team placed blacktip, bonnethead and nurse sharks into a specially engineered tank where the water flowed directly at them. The scientists then put a prey fish or shrimp at the reverse end of the tank, released the hungry shark and followed the shark’s motions towards the prey.
Next, the team briefly blocked the sharks’ senses individually during a series of experiments using eye patches, nose plugs, antibiotics to hinder their lateral lines and electrically insulating materials to hide the electrosensory pores on their snouts.
“We had hundreds of video clips to sort through, and we had to get just the right angle to see when the shark was capturing the prey,” Gardiner said.
The researchers saw, unlike the other two species, nurse sharks did not identify their prey if their noses were clogged. The study team said this finding makes sense as nurse sharks identify prey in the dark and often suck hidden prey out of cracks in rocks. The other two sharks scoop up prey in daylight – explaining their reliance on vision over smell.
The study team also found that when the sharks’ vision were blocked, they could somewhat align their strikes at close range using their lateral lines. When both vision and lateral lines were blocked, blacktip and bonnethead sharks could not locate prey, but nurse sharks could using their sense of smell. With electroreception blocked, sharks often did not capture prey.
“Sharks (…) are not unique in their sensory guidance of hunting: They exploit information fields available to all marine species. Thus, the results may be seen as a general blueprint for underwater hunting, modifiable by habitat and by the behavioral specializations of many different aquatic animals from lobsters to whales,” the study team wrote in their report.
“I think the sharks’ abilities to switch between different senses may make them more resilient in the wild. They may be more flexible and better adapted to deal with environmental changes – but not all human impacts. Overfishing is still overfishing," Gardiner said.