Sharks have a rep for hunting alone. They're like killer whales, for example, who hunt in pods like a pack of wolves. But a group of researchers studying lemon sharks in Bimini, Bahamas, have found that juvenile lemon sharks spend more time in close proximity of each other than previously thought.
The study, conducted by biologist Tristan Guttridge, who recently received his PhD from the University of Leeds, and renowned shark biologist Samuel "Doc" Gruber, was meant primarily to test how acoustic transmitters and receivers could work to quantify interactions of sharks in the wild.
The information gathered from this kind of tech could not only lead to a deeper understanding of shark behavior, which is still largely unexplained, but also make it easier to protect populations of this animal.
Electronic transmitters are not new to shark research. Scientists have attached GPS or other electronic tags to sharks to track their movements in the ocean. But these devices are different. Instead of communicating with a fixed receiver located on a researcher's boat, for example, they communicate with other devices attached to other sharks.
Developed by Sonotronics, an ultrasonic tracking equipment manufacturer based in Tucson, AZ, the prototype acoustic receivers are designed to listen for a signal from another transmitter, and when it finds one, record it using a unique timing sequence, so that each shark can be easily identified. The devices log the date and time they encounter another transmitter, and can be programmed to communicate with each other at specific distances.
At this time, sharks have to be recaptured in order to obtain the data collected on its receiver. But other techniques are possible. For example, some researchers use sensors that have a mechanism, which detaches the device from the shark after a programmed amount of time. The device floats to the surface and emits a radio signal that can be tracked by equipment on a boat, which then navigates to the device to retrieve it.
In field trials performed earlier this year (full article), the sonic sensors were set to relay information within a distance of four meters, which is equivalent to four body lengths of a shark. The team hypothesized that if the receiver worked within that distance and for a significant amount of time, it would indicate unique behavior, said Sonotronix president Marlin Gregor.
In fact field trials showed just that. And "although there wasn't enough data to make any firm conclusions about juvenile lemon shark grouping behaviour in general, it did provide some interesting preliminary results enhancing the claim for the technology's future use," write the researchers in their study. Namely, that one juvenile lemon shark made contact with nine other juvenile on multiple occasions and for up to seven minutes at a time.
While there is no way to know exactly what the sharks were doing during those close encounters, Guttridge says that from his observations he has seen the sharks follow each other, circle each other and hang out.
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The unique part of the biologists' work is the combination transmitter-and-receiver setup. Making the shark the receiver improves the scientists' ability to determine how much time the animals spend together and how close they are, and that could ultimately help protect them.
"On a bigger scale, sharks that form aggregations are especially vulnerable to overfishing. Understanding where and why they’re forming will help with habitat management," Guttridge told me.
Another group of scientists has been making headway with shark transmitters and receivers, too, although with different gains. Last year, Kim Holland at the University of Hawaii led a team that affixed prototype transmitter/receiver tags on four free-swimming sharks to discover the remote areas the sharks traveled to, and published their findings (PDF) in Endangered Species Research.
The more we learn about shark behavior, the less they'll be perceived as rote killers, Gregor says.
Photos: Adult lemon shark (top). Tristan Guttridge and Bimini Biological Field Station manager Katie Gledhill implant a juvenile lemon shark with a proximity receiver (bottom). Credit: Rene Frederick/Getty Images (top), and Matt Potenski (bottom).
Tags: Conservation, Green Tech, Sensors, Wearable Computers
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