An investigation of acoustic deterrent devices to reduce cetacean bycatch in an inshore set net fishery

Tests were conducted aboard small (<10 m long) static net fishing vessels targeting monkfish off the coast of Britain to determine the response of cetaceans to pingers.  AQUAmark 100 pingers were positioned at 200 m intervals on the net and acoustic click detectors (C-PODs) were placed at the end of 1 km tiers of the net to determine the response of cetaceans to the pingers.  Only one harbour porpoise was incidentally caught during these trials and there was a significant reduction in the number of porpoise clicks recorded at nets with pingers compared to those without.  Additional tests were conducted to determine habituation.  For these tests, modified pingers, active for alternate seven hour periods, were attached below click detectors at one site with strong tides and loud ambient noise and one at a quite site.  The results of this part of the study showed the pinger effect was stronger at the quiet site and that were was no habituation.  In addition, there was evidence of exclusion of porpoises following pinger use for as much as seven hours.