Further work citing morphological data ( Budelmann, 1976) and behavioral observations outlined why squid are probably sensitive to sound ( Hanlon and Budelmann, 1987). These hypotheses stimulated the proposal that squid evolved to be ‘deaf’ to the effects of intense sound exposure ( Moynihan, 1985). It has also been hypothesized that squid may be stunned by, and therefore perhaps be sensitive to, intense ultrasonic echolocation clicks produced by foraging toothed whale predators ( Norris and Møhl, 1983). The modality and frequency range indicate that squid probably detect acoustic particle motion stimuli from both predators and prey as well as low-frequency environmental sound signatures that may aid navigation.Īnecdotal evidence initially suggested squid may be attracted to 600 Hz pure tones ( Maniwa, 1976), and one relative, the cuttlefish ( Sepia officinalis), was reported to have startle responses to 180 Hz stimuli ( Dijkgraaf, 1963). Both the AEP response characteristics and the range of responses suggest that squid detect sound similarly to most fish, with the statocyst acting as an accelerometer through which squid detect the particle motion component of a sound field. Evoked potentials were extinguished at all frequencies if (1) water temperatures were less than 8☌, (2) statocysts were ablated, or (3) recording electrodes were placed in locations other than near the statocysts. At the best frequencies, AEP amplitudes were often >20 μV. Responses were obtained between 30 and 500 Hz with lowest thresholds between 100 and 200 Hz.
Evoked potentials were generated by both stimuli and consisted of two wave types: (1) rapid stimulus-following waves, and (2) slower, high-amplitude waves, similar to some fish AEPs. Responses were determined using auditory evoked potentials (AEPs) with electrodes placed near the statocysts. Sound field pressure and particle motion components were measured from 30 to 10,000 Hz and acceleration stimuli were measured from 20 to 1000 Hz. Here we quantify the acoustic sensitivity of the longfin squid ( Loligo pealeii) using near-field acoustic and shaker-generated acceleration stimuli. Although hearing has been described for many underwater species, there is much debate regarding if and how cephalopods detect sound.
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