Famous for their acute sense of smell, sharks have long struck fear into the hearts of swimmers with their incredible predatory skills. However, a new USF study suggests that it is not the potency but the pace with which a scent reaches a shark that determines their path.
Jayne Gardiner, a Ph.D. candidate in USF’s Department of Integrative Biology, discovered that sharks can detect which nostril first receives the scent of food and then swim in that direction – a discovery that not only sheds light on their hunting process, but also could provide the information needed to help humans hunt for underwater sources of pollution using odor-guided robots.
“There has always been an interest in having underwater vehicles that we can use to locate chemical sources like explosives, a chemical leak or an oil spill,” Gardiner said. “We can send them into an environment that humans can’t go into and because animals – sharks in particular – are so good at sniffing things out, people have tried in the past to make robots that mimic these animals.”
One such attempt was based on research conducted 25 years ago by colleagues of Jelle Atema, Gardnier’s master’s adviser at the Boston University Marine Program and co-author of the article published in Current Biology last week on the study.
That robot was unsuccessful because it attempted to track the concentrations of underwater odors – a popular idea among researchers that has some flaws, Gardiner said.
“Most people would expect that odor be very strong at the source and weaker as it moves away, but that’s really not the case when you have flowing water,” she said. “It really breaks up the odor and mixes it around and becomes a crazy chaotic plume so an animal could be really mislead as to where an odor is coming from.”
When analyzing previous studies that charted the effects of odor concentrations on sharks, Gardiner noticed that the speed with which an odor was received was the biggest factor in determining their routes.
“I had for a long time been intrigued by the idea that even very small fishes have two nostrils that are separated by maybe only one millimeter and this whole notion that animals would use concentration differences seemed unattainable,” Atema said. “We know that, in hearing, arrival time differences are very important and the brain is very capable of extracting very fast time differences, so I was always very interested in discovering how that would work – how animals could rely on time differences and that’s when we decided to do the study.”
Their study, which was funded by the National Science Foundation, began two years ago, Gardiner said, and outfitted eight small dogfish sharks with equipment stitched to their heads with a piece of Velcro.
“It almost looks like head gear,” she said. “It’s basically a frame that attaches to the top of the head of the animal and wraps around the snout so tubing can fit just inside the nostril of the animal. It’s connected to two syringe pumps that push the odor through and control odor and timing, synched by a computer.”
They found that the animals have between 0.1 and 0.5 seconds to determine which direction to turn on the hunt for food or else they leave it up to chance. This may provide the information necessary to create maneuverable underwater robots, but it has yet to provide any implications for the animals’ interactions with humans in the water, she said.
However, Gardiner and Atema’s work is not finished yet.
“I’m still working with sharks,” Gardiner, who came to USF after earning her degree from Boston University and working for the Canadian government, said. “This is just one small piece of a much larger comprehensive approach at shark sensory biology and how they integrate information from all of their senses while feeding.”