January 10, 2013
Shark Embryos Use Natural Repellent To Avoid Predators
[Watch Video: Embryonic Bamboo Sharks Respond To Predators]
Brett Smith for redOrbit.com - Your Universe Online
Drawing on the same electroreceptors that adult sharks use to find prey, tiny embryonic bamboo sharks can sense predators and completely stop any movement, essentially ℠playing possum,´ according to a new report by Kempster and his Aussie colleagues, which was published in the latest edition of the open access journal PLOS ONE.
Previous research on the spotted catshark suggested this type of behavior in shark pups, but the new study reveals this reaction to a perceived predator in great detail.
"This is the first study that shows a shark embryo's ability to detect and 'hide' from a predator by staying completely still and stopping its breathing," Kempster told Michelle Warwicker of BBC News.
All living creatures give off a small electrical field and upon detecting one from a potential predator the shark embryos stopped gill movements and curled their tails around their bodies. The developing sharks use their gills and beat their tails as part of their respiration process. However, these processes generate odor cues and small water currents that can give away the embryo's position.
Kempster, who was looking for a better shark repellent, decided to investigate how sharks react to weak electronic fields. Adult sharks make for poor test subjects, so the Australian biologist used embryonic sharks that were confined to small leathery egg sacs.
"Despite being confined to a very small space within an egg case where they are vulnerable to predators, embryonic sharks are able to recognize dangerous stimuli and react with an innate avoidance response,” Kempster said.
Kempster and his colleagues also found that the tiny sharks remembered the electrical field signals if they were exposed to them again within 40 minutes. These subsequent responses were notably not as strong as the sharks´ initial ones. This finding would have ramifications for the design of a new electrical field-based shark repellant as the current would need to be changed over a 20- to 30-minute period.
"This means that sharks may become conditioned to current repellent devices if the signals that these devices produce do not change substantially over time," Kempster said in his BBC interview.
The Aussie scientist said that a new shark repellent would not only protect humans–it could also prevent sharks from harm as well. As frequent, yet inadvertent, victims of commercial fishing efforts, shark populations have often been on the wrong end of their relationship with humans. A more effective repellent could help to keep sharks from being in the wrong place at the wrong time.
Keeping sharks out of harm´s way is one goal for Kempster´s research. He is also founder of the shark conservation group Support Our Sharks and said his findings may provide "a stepping stone" to producing more effective repellents.
"It is my goal to show the world that there is more to sharks than just a sharp row of teeth, and that we have so much more to learn from these amazing animals,” he said.