A previous study has reported that Atlantic cod can be conditioned
to detect ultrasonic sound pulses of high intensity. This capability
has been proposed as a mean for detection and avoidance of echolocating
toothed whales that emit intense ultrasonic clicks. In this
study, we use acoustic playbacks to test the hypotheses that
unconditioned cod can detect and respond to intense ultrasound
from toothed whales and from echosounders. Intense ultrasound
exposure of 210 dB re. 1µPa (pp) did not cause a short-term stress
response in the form of bradycardia in unconditioned cod. Free-swimming cod
exposed to ultrasonic clicks and echosounder pulses with received
levels of more than 204 dB re. 1 µPa (pp) did not elicit
flight responses as seen in ultrasound detecting Alosinae. Furthermore,
we tested the debilitating effects of high intensity ultrasound
on swimming cod with no detected changes in swimming ability
when exposed to more than 213 dB re. 1 µPa (pp). It is concluded
that intense ultrasound exposure induces neither an antipredator
nor a stress response in Atlantic cod, and that echosounder
pulses and biosonar clicks therefore most probably play no ecophysiological
role in wild cod populations.
