Noise pollution impacts the movement of Yangtze's Finless Porpoises, which rely on sound to move around in the busy river. Scientists find that the porpoises may be in danger.
Asia's longest and busiest river, the Yangtze, endangers the porpoises' survival in the Chinese channel because of the heavy traffic there.
The finless porpoises, just like other mammals living in the sea and freshwaters, depend on their auditory senses to communicate with other animals and navigate the muddy waters.
In this new research, scientists determined the variations of sizes and shapes of the head of toothed cetaceans among different species. They were able to prove that this is a major factor in the animals' sound perception and frequency sensitivity to different noises.
The researchers came upon the disturbing discovery that the Yangtze's finless porpoises could be having difficulty in detecting sound and navigating the busy river. This could mean that this species would become extinct.
Aran Mooney, lead author of the study and a biologist, said that their team wants to understand how they may be affected by noise. "We've learned that there's more variation than we've taken into account on how different species hear."
The scientists conducted tests on the finless porpoises in the Yangtze River and tried to find how different they are from other toothed cetaceans using acoustic sensitivity exams and CT scans. The method of study used was very similar to human infant examinations.
The subjects were two porpoises who used to be in the wild in the Yangtze but were captured and taken cared of for years inside the facilities of China's Institute of Hydrobiology in Wuhan.
They found that the finless porpoises like their fellow toothed marine animals do not have ears. They only use sound by detecting frequencies and echoes through its jaw, throat, head and acoustic fat. In contrast, their acoustic fat looks like discs and are thicker than other toothed cetaceans.
"Porpoises, like babies, can't tell us if they can hear in their left or right ear, so we measure their hearing physiologically from the surface of the skin," Mooney said.
"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," he added.
The study was published in the Journal of Experimental Biology.
