Observations of cod reaction to trawling noise

Observations made from a stationary echo sounder, passed by a trawling vessel, clearly demonstrate the flight reaction of cod as a response to the noise from the vessel. Horizontal dispersal and downward swimming has been observed to starts as early as 200 m in front of the vessel propeller, and a descent speed of nearly 17 mjmin has been recorded. The avoidance reaction was seen at depths from 50 - 170 m depth, gradually diminising with increasing depth. Similar, but and weaker responses were also observed during general passages without trawl