To block a nose, they'd use pieces of cotton soaked with petroleum jelly. To block the sharks' vision, the researchers covered the animals' eyes with small pieces of black plastic.
In addition to sight and smell, sharks use their head and body (or lateral line system) to sense water movements, so researchers treated those senses with an antibiotic to destroy the hair cells that make up the receptors. (The cells grow back after a couple of weeks.)
The researchers also used electrically insulating material to cover the electrical connections between the skin and the water, which sharks also use as a sense. (Electrosensory systems are used to find naturally occurring electrical stimuli, and is common among creatures in water since water is a much better conductor than air.)
Building better shark repellant
The sharks were even more adaptable than the researchers had expected. For example, blacktips and bonnetheads found the prey even after their sense of smell was blocked. The nurse sharks did not find the prey, which shows they do rely on their sense of smell in the wild. In captivity, nurse sharks can retrain their systems to rely on visual cues, Gardiner said.
However, human impacts on sharks' environment are affecting the animals' senses, scientists say. For instance, pollutants are hard on the sharks' eyes and noses, and heavy metals and antibiotics can damage the lateral line system.
Gardiner hopes to use her findings to understand how adult sharks navigate back to their birthplace when they are ready to give birth.
Gardiner's work, which was a part of her doctoral research at the University of South Florida, was published today (April 2) in the journal PLOS ONE.
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