REACTIONS OF PENNED HERRING AND COD TO PLAYBACK OF ORIGINAL, FREQUENCY-FILTERED AND TIME-SMOOTHED VESSEL SOUND

The behavioural responses of penned cod (Gadus morhua L.) and herring (Clupea harengus L.) to playback of original, frequency-filtered and t ime-smoothed sound recordings from a trawler were tested. Avoidance re actions of both cod and herring were observed during playback of the o riginal, 60-300 Hz and 300-3000 Hz spectra, but hardly to the 20-60 Hz spectrum. The duration of responses of cod was longer to original tha n to time-smoothed sound. The conclusion is that the main determinant for triggering avoidance reactions of cod and herring is vessel sound level within the most sensitive frequency region, although other sound characteristics, such as temporal structure, also seem to be of impor tance.