Sharks like the brownbanded bamboo shark have photoreceptors that let them search for potential prey while lurking through the ocean, but when they're still embryos these receptors can also help prevent them from becoming the prey. According to new research from the Oceans Institute at the University of Western Australia, the sharks, which spend up to five months inside a tiny egg-like sac outside of their mother's body, can still sense danger and react by keeping very still. It's what the researchers call an "innate avoidance response."
This was determined by stimulating embryos with "very weak" electrical fields and studying their reactions. However, the sharks were also able to recognize when they were repeatedly subjected to the same electrical field, and their response lessened with each subsequent exposure. According to study author Ryan Kempster, this could be very useful information when it comes to developing shark repellents. "This means that sharks may become conditioned to current repellent devices if the signals that these devices produce do not change substantially over time," he told the BBC.