Chinese Biologists Discover Variations in Hearing of Dolphins and other Marine Mammals

Chinese scientists are researching the hearing ability of Yangtze finless porpoise and the impact , an endangered dolphin species, with only about a 1000 of them left.

The researchers are from the WHOI (Woods Hole Oceanographic Institution)  and the Institute of Hydrobiology of the Chinese Academy of Sciences in Wuhan and some other marine biologists. Aran Mooney, a biologist at the Woods Hole Oceanographic Institution (WHOI) was the lead author of the study.

"We want to understand how they may be impacted by noise," Mooney said in a news release.

Hearing is of crucial importance for dolphins and other marine mammals as it aids them in finding food for themselves, communicating, navigating in the dark, deep and muddy ocean environment. A little is known about the hearing abilities of bottlenose dolphins as they can be observed in aquaria and marine parks. Information regarding the hearing abilities of more than 70 other species like the toothed whales or odontocetes is unknown.

This data is required by the natural resource managers and regulators for formulating decisions regarding aquatic noise pollution in order to protect these marine species from disturbances arising from high-traffic activities such as shipping, construction and dredging.

Recently,  around hundreds of melon-headed whales were stranded by sonar mapping  done by an ExxonMobil survey vessel in northwest Madagascar, according to a report.

The researchers got some Yangtze finless porpoises from the river to the research facility at the Institute of Hydrobiology of the Chinese Academy of Sciences in Wuhan, China.  Acoustic sensitivity tests and CT scans were conducted on these endangered species. The results were then compared with that of bottlenose dolphins.

"The exam results showed that the finless porpoises are sensitive to sound nearly equally around their heads while bottlenose dolphins and beluga whales exhibit a substantial 30-40 decibel difference in sound sensitivity from their jaw to other parts of their head," the researchers stated.

It was also found that the Yangtze finless porpoise are capable of hearing omni-directionally, which creates difficulty in differentiating the various noises coming at them underwater.

"In a noisy environment, they'd have a hard time hearing their prey or their friend. It makes it more difficult for them to conduct basic biological activities such as foraging, communicating, and navigating in the river," Mooney said.