Beluga whales live in the world's cold northern seas, where they endure months of perpetual darkness.
“So they have to use sound, rather than sight, in order to find their way around.” That's Aran Mooney, a marine biologist at Woods Hole Oceanographic Institution, in Massachusetts. He says belugas have really fast hearing, too: “Sound underwater travels five times faster than it does in air. And so those guys have to basically perceive and utilize sound five times faster than we do.”
He and his colleagues traveled to Bristol Bay, Alaska, to test belugas' hearing in the wild. They captured seven belugas for routine physicals. And played them a series of frequencies, while measuring the whales' brain activity with electrodes.
Turns out the whales' hearing was sharp, and similar to that of captive belugas. Which means they could appreciate sound ranging from about 4 kilohertz to 150—a frequency nearly eight times higher than the upper limit of our ears. The results are in The Journal of Experimental Biology. [Manuel Castellote et al, Baseline hearing abilities and variability in wild beluga whales (Delphinapterus leucas)]
The older belugas tested in this survey still had decent hearing too. But that might not be the case for belugas living in noisier Cook Inlet, near Anchorage.
“There's a lot of military activities, a lot of commercial activities in Cook Inlet, and those animals are known to be declining at a rate of about two percent per year. And we think noise is a major stressor to those animals.”
And now that researchers know what wild belugas should be able to hear, they can test Cook Inlet belugas—to see whether that underwater noise is, literally, deafening.
[The above text is a transcript of this podcast.]