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Standing next to the speakers at a loud concert can leave your ears ringing. Some squid, it turns out, are much the same: listening to just 15 minutes of boat noise makes hummingbird bobtail squid temporarily deaf. Even though the animals can regain their hearing within hours, the ever-present din of human noise pollution means squid may never get the chance to recover.
Squid’s noise sensitivity stems from the structure of their hearing organs, a pair of tiny fluid-filled sacs called statocysts. Similar to the human inner ear, statocysts can detect vibrations, gravity, and the animal’s orientation in its watery surroundings. Although our understanding of squid physiology is still developing, it’s likely that the delicate structures are easily damaged by loud, low-frequency sounds.
In a recent study, Rosalyn Putland, an underwater noise researcher from the Centre for Environment, Fisheries and Aquaculture Science in the United Kingdom, exposed lab-cultured squid to 15-minute audio recordings of an idling boat—a typical sound for squid in their natural habitats. To squid, the diesel engine’s 150-decibel thrum, muffled by the water, would be roughly the volume of a noisy restaurant or heavy road traffic.
Squid are “super inquisitive,” says Putland, and each has its own personality, so she wasn’t surprised when video footage captured slightly different responses to the noise. Some squid breathed more slowly—a tactic the animals use to hide from predators—suggesting they may have been on alert. But others appeared unbothered. None jetted, inked, or changed colors, the typical signs of cephalopod stress.
But when Putland examined the squid’s hearing, the results were quite different. Using electrodes placed under the animals’ skin, she measured the cephalopods’ sensitivity to single-tone sounds at different frequencies. The test was like a human hearing test, Putland explains, but in place of a verbal response she monitored electrical signals from the squid’s nervous system that signaled when the animals were responding to the sound.
After exposure to boat noise, the squid had trouble detecting frequencies between 100 and 1,000 hertz, which span the majority of their hearing range. It took up to two hours for the squid to recover. While squid are not known to communicate through sound, this low-frequency range is where predators like dolphins, whales, and fish vocalize, meaning the squid’s sudden deafness could lead to deadly consequences. The discovery builds on previous research, which shows that heavy noise pollution can irreparably damage squid statocysts, leaving them permanently deaf.
To Kate Feller, a visual and sensory ecologist at Union College in New York who was not involved with the study, the research suggests there might be ways to use this information to protect squid.
“What’s uplifting is the finding that they recover in a few hours,” says Feller. “Giving the animals a break,” like limiting the times of day for vessel traffic or underwater drilling in a certain area, she says, “is the key because chronic exposure is going to lead to chronic long-term damage.”