Researchers at the University of Florida have been working with rescued dolphins to help determine why they became beached or entangled in fishing nets despite their highly advanced sonar abilities.
They found almost 60 percent of stranded bottlenose dolphins now recovering in Florida rescue facilities were severely or profoundly deaf.
“We used the same methods to test the dolphins as is used to measure hearing in human babies,” said the study’s lead researcher, Dr. David Mann of the University of South Florida. “Like human babies, some dolphins are born deaf and can probably survive well with their mothers until weaned, but hunting on their own can be problematic, although some do seem to adapt and manage.”
“The researchers affixed sensors to the creatures’ heads with suction cups, which could detect electrical activity in the brain. They then played a series of tones: If the animals could hear them, the sensors would detect millions of neurons firing to process the sound” reports the Washington Post.
Causes of deafness in whales and dolphins are similar to those in humans and range from exposure to chronic noise from busy shipping lanes, disease, trauma and ageing, reports EarthTimes.
Although conservationists might be inclined to blame Naval sonar activities when mass strandings of marine mammals occur around the world, this might not be warranted.
Darlene Ketten, the world foremost expert on marine mammal hearing, reports that fewer than 300 animals have been stranded in association with naval exercises in the last 50 years.
This pales in comparison to the 100,000 and 400,000 animals that are injured and killed as a result of being caught up as bycatch in fishing nets.
Mann and his research team concluded that it’s possible that animals with damaged hearing might be more likely to strand if they cannot orientate themselves properly.
As a result, Mann recommends that the hearing of all cetaceans in rehabilitation be tested to find out if they’re deaf, and to help determine whether or not they will be able to survive in the wild.
The high cost of marine mammal rehabilitation could prevent scientists from spending too much time working with dolphins and other creatures unlikely to survive because of hearing loss.
Image Credit: Flickr - Skyfisher