Toothless Whales Use Fat To Listen
April 19, 2012

Toothless Whales Use Fat To Listen

Scientists have long understood the way dolphins and toothed whales have been able to hear underwater. These animals have a special type of fat surrounding their jaws which can relay sounds from the ocean to their ears. Now, thanks to a new study, scientists are able to understand how their toothless grazing cousins, the baleen whales are able to hear without these sound-enhancing jaws.

Toothed whales and dolphins are able to use their jaws in conjecture with echolocation in order to communicate with one another and find their prey. Baleen whales, on the other hand, generally graze on zooplankton, and scientists had concluded the baleen whales simply didn´t have a need for such a sophisticated hearing system.

Now, according to a new study, scientists at Woods Hole Oceanographic Institution (WHOI) have discovered some baleen whales actually do have the specialized fat near their jaws. The new study was published on April 10,2012 in The Anatomical Record.

With the data from this study, the scientists now propose toothed whales may not be the only whales to use this jaw fat to transmit sounds in the water. Furthermore, the fats found in these jaws may share a similar evolutionary origin.

Baleen whales, unlike toothed whales and dolphins, are very large and as such are not kept in captivity. They are rarely stranded on beaches, and when they are, they decompose much more quickly than their cousins. As such, specimens of the large grazing whale are not easily found and little progress had been made in understand how these animals hear.

Maya Yamato, a graduate student in the MIT/WHOI Joint Program in Oceanography was the lead author of the new study. According to the press release announcing the new study, Yamato had received 7 heads of similar whales, known as minke whales, which had stranded and died on beaches on Cape Cod. Yamato worked together with the International Fund for Animal Welfare´s (IFAW) Marine Mammal Rescue and Research unit in Yarmouth Port, Mass.

Yamato then scanned the heads using both CT and MRI scanners.

With this data, Yamato and her team were able to create 3D images of the whale´s internal anatomy. The researchers decided to use the scanning techniques in order to leave bones and soft tissues on the heads intact and in their natural positions. The resulting 3D images gave researchers “an unprecedented view of the internal anatomy of these animals,” according to the researchers.

Yamato and her team then took the minke whale heads to be dissected in the necropsy facility at the Marine Mammal Center at WHOI. The resulting data from the dissection, in combination with the scans, showed the minke whales had “a large, well-formed fat body” on the jaw connecting to the ears, providing the potential for these whales to hear in the same way as their toothed cousins.

“This is the first successful study of intact baleen whale head anatomy with these advanced imaging techniques,” said WHOI Senior Scientist Darlene Ketten, director of the CSI lab at WHOI and co-author on the paper. “It really is an important addition to our understanding of large whale head and auditory systems.”