14 DAY TRIAL // Marine biologists from the Taiwan National Academy of Science in Taipei have been finally able to end a century-old dispute recently, when they have managed to establish for a fact that all cephalopods, including squids, octopuses, cuttlefish and nautiluses, can hear sounds underwater. The debate was sparked by the fact that the animals did not have gas-filled chambers like humans, and therefore would have nothing to process the sound waves coming to them with. This also means that the pressure component of the sound is unknown to these creatures.
Unlike fish, which can use their air-filled swim bladder to locate the source of a sound, octopuses and squids lack it completely, which suggests that they use other mechanisms to make out sounds. But the find raises the tantalizing possibility that the creatures use auditory input to locate prey, steer clear of predators, and also for communications within the species. In previous studies, it has been demonstrated that blind octopuses are able to detect sounds inside water, be they from an incoming boat, or from taps drummed on the walls of the tanks they were in.
According to Taiwanese researcher Hong Young Yan, from the National Academy, the cephalopods may be using an organ known as the statocyst to record sounds. This sac-like chamber contains peculiar mineralized components, alongside strands of sensitive hair, which may act like the ones humans have in their inner ears. Moving these hairs in humans causes a difference of electrical potential in auditory nerves, which is transmitted to the brain and processed into the auditory sensation.
The studies performed at the Academy revealed the fact that squids could hear sounds in the 400Hz-to-1,000Hz range, which is equivalent to lower notes in the human hearing range. The latter spans from about 20Hz to 20,000Hz. The squids can hear a little better than the octopuses, with a frequency range of between 400Hz and 1,500Hz. The research is described in the latest issue of the journal Comparative Biochemistry and Physiology, Part A.
“That indicates that squid have a better hearing capability than the octopus. Interestingly though, both species hear best at a frequency of 600Hz,” Yan said, quoted by the BBC News. “The key question which I would like to investigate is what kind of sounds are they listening to? Perhaps they listen to sound to evade predators and can eavesdrop to sounds made by their prey. Or, perhaps they even could make sounds to communicate among themselves.”