Aran Mooney was the Principal Investigator on a project to determine the hearing sensitivity of squid. An article this week in the Woods Hole Oceanographic Institute newsletter describes the research and its importance to commerce and ecology.
We know from earlier studies conducted by Robert McCauley et. al. that airgun surveys would significantly alter squid behavior at 3-5km distant, but their paper published in 2000 was a behavioral study of various animal’s responses to airguns so it did not include an examination of the hearing organs of squid.
This is where the Mooney et. al. paper digs in, and they found that the dominant squid hearing organ is akin to a rudimentary cochlea found in mammals, with a tissue envelope lined with hair cells or ‘cilia’ that translate physical motion (from acoustical energy) into electro-chemical nerve impulses.
Their studies show that the squid (sedated into cooperation) have nervous systems that respond to frequencies below 500 Hz. The testing uses a technique called “Auditory Evoked Potential” or “AEP” which measures electrical activity of the nervous system in response to acoustical stimulus.
While the studies do not show nervous system response above 500 Hz, noise limitations in AEP testing and the impacts of sedation may not accurately reflect the response of squid hearing systems to higher frequencies. It might be worthwhile checking in on squid behavioral responses to higher frequency signals – such as the foraging clicks of dolphins and beaked whales (among their top predators).
In any event Aran’s research will be useful in determining the impacts of various noises on squid – an important link in the entire ocean food chain.