Handout photo of tasselled wobbegong shark lying on the sea floor with the head of a brown-banded bamboo shark in its mouth at Great Keppel Island (Photo : Reuters)
In pursuit of crafting effective shark repellant technology, Ryan Kempster of the University of Western Australia tested the impact of electromagnetic fields on brown-banded shark embryos and discovered that fetuses in the later stages of development play dead in the presence of potential predators.
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"Despite being confined to a very small space within an egg case where they are vulnerable to predators, embryonic sharks are able to recognise dangerous stimuli and react with an innate avoidance response," says Kempster. "Knowledge of such behaviours may help us to develop effective shark repellents."
The brown-banded shark gestates in an egg case independent of its mother, a curiosity among the many species of sharks. Once the embryo's ampullae of Lorenzini form, the shark is able to detect nearby electrical currents which will later play an integral part of its hunting behavior.
Kempster exposed the embryos to electrical signals that mimicked the signature of larger predators and found that the sharks ceased moving and minimized any cues that would alert any creatures on the prowl to its location.
"[The embryo] shuts down any odor cues, water movement, and its own electrical signal," says University of Washington neuroecologist Joseph Sisneros.
Ryan explains his methodology, noting that "It's very hard to test this in the field because you need to get repeated responses. But we could use embryos because they're contained within an egg case."
As for the study's practical use, Kempster hopes that his research will help preserve dwindling worldwide shark populations by setting up weak electrical barriers around fish nets to reduce what is known as bycatch. The student's research also found that the signal must be altered over time to retain its usefulness.
"If you were using a shark repellant, you would need to change the current over a 20 to 30 minute period so the shark doesn't get used to that field."
The research was originally published in the journal PLOS One.